1menu "printk and dmesg options" 2 3config PRINTK_TIME 4 bool "Show timing information on printks" 5 depends on PRINTK 6 help 7 Selecting this option causes time stamps of the printk() 8 messages to be added to the output of the syslog() system 9 call and at the console. 10 11 The timestamp is always recorded internally, and exported 12 to /dev/kmsg. This flag just specifies if the timestamp should 13 be included, not that the timestamp is recorded. 14 15 The behavior is also controlled by the kernel command line 16 parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst 17 18config CONSOLE_LOGLEVEL_DEFAULT 19 int "Default console loglevel (1-15)" 20 range 1 15 21 default "7" 22 help 23 Default loglevel to determine what will be printed on the console. 24 25 Setting a default here is equivalent to passing in loglevel=<x> in 26 the kernel bootargs. loglevel=<x> continues to override whatever 27 value is specified here as well. 28 29 Note: This does not affect the log level of un-prefixed printk() 30 usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT 31 option. 32 33config MESSAGE_LOGLEVEL_DEFAULT 34 int "Default message log level (1-7)" 35 range 1 7 36 default "4" 37 help 38 Default log level for printk statements with no specified priority. 39 40 This was hard-coded to KERN_WARNING since at least 2.6.10 but folks 41 that are auditing their logs closely may want to set it to a lower 42 priority. 43 44 Note: This does not affect what message level gets printed on the console 45 by default. To change that, use loglevel=<x> in the kernel bootargs, 46 or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value. 47 48config BOOT_PRINTK_DELAY 49 bool "Delay each boot printk message by N milliseconds" 50 depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY 51 help 52 This build option allows you to read kernel boot messages 53 by inserting a short delay after each one. The delay is 54 specified in milliseconds on the kernel command line, 55 using "boot_delay=N". 56 57 It is likely that you would also need to use "lpj=M" to preset 58 the "loops per jiffie" value. 59 See a previous boot log for the "lpj" value to use for your 60 system, and then set "lpj=M" before setting "boot_delay=N". 61 NOTE: Using this option may adversely affect SMP systems. 62 I.e., processors other than the first one may not boot up. 63 BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect 64 what it believes to be lockup conditions. 65 66config DYNAMIC_DEBUG 67 bool "Enable dynamic printk() support" 68 default n 69 depends on PRINTK 70 depends on DEBUG_FS 71 help 72 73 Compiles debug level messages into the kernel, which would not 74 otherwise be available at runtime. These messages can then be 75 enabled/disabled based on various levels of scope - per source file, 76 function, module, format string, and line number. This mechanism 77 implicitly compiles in all pr_debug() and dev_dbg() calls, which 78 enlarges the kernel text size by about 2%. 79 80 If a source file is compiled with DEBUG flag set, any 81 pr_debug() calls in it are enabled by default, but can be 82 disabled at runtime as below. Note that DEBUG flag is 83 turned on by many CONFIG_*DEBUG* options. 84 85 Usage: 86 87 Dynamic debugging is controlled via the 'dynamic_debug/control' file, 88 which is contained in the 'debugfs' filesystem. Thus, the debugfs 89 filesystem must first be mounted before making use of this feature. 90 We refer the control file as: <debugfs>/dynamic_debug/control. This 91 file contains a list of the debug statements that can be enabled. The 92 format for each line of the file is: 93 94 filename:lineno [module]function flags format 95 96 filename : source file of the debug statement 97 lineno : line number of the debug statement 98 module : module that contains the debug statement 99 function : function that contains the debug statement 100 flags : '=p' means the line is turned 'on' for printing 101 format : the format used for the debug statement 102 103 From a live system: 104 105 nullarbor:~ # cat <debugfs>/dynamic_debug/control 106 # filename:lineno [module]function flags format 107 fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012" 108 fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012" 109 fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012" 110 111 Example usage: 112 113 // enable the message at line 1603 of file svcsock.c 114 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 115 <debugfs>/dynamic_debug/control 116 117 // enable all the messages in file svcsock.c 118 nullarbor:~ # echo -n 'file svcsock.c +p' > 119 <debugfs>/dynamic_debug/control 120 121 // enable all the messages in the NFS server module 122 nullarbor:~ # echo -n 'module nfsd +p' > 123 <debugfs>/dynamic_debug/control 124 125 // enable all 12 messages in the function svc_process() 126 nullarbor:~ # echo -n 'func svc_process +p' > 127 <debugfs>/dynamic_debug/control 128 129 // disable all 12 messages in the function svc_process() 130 nullarbor:~ # echo -n 'func svc_process -p' > 131 <debugfs>/dynamic_debug/control 132 133 See Documentation/admin-guide/dynamic-debug-howto.rst for additional 134 information. 135 136endmenu # "printk and dmesg options" 137 138menu "Compile-time checks and compiler options" 139 140config DEBUG_INFO 141 bool "Compile the kernel with debug info" 142 depends on DEBUG_KERNEL && !COMPILE_TEST 143 help 144 If you say Y here the resulting kernel image will include 145 debugging info resulting in a larger kernel image. 146 This adds debug symbols to the kernel and modules (gcc -g), and 147 is needed if you intend to use kernel crashdump or binary object 148 tools like crash, kgdb, LKCD, gdb, etc on the kernel. 149 Say Y here only if you plan to debug the kernel. 150 151 If unsure, say N. 152 153config DEBUG_INFO_REDUCED 154 bool "Reduce debugging information" 155 depends on DEBUG_INFO 156 help 157 If you say Y here gcc is instructed to generate less debugging 158 information for structure types. This means that tools that 159 need full debugging information (like kgdb or systemtap) won't 160 be happy. But if you merely need debugging information to 161 resolve line numbers there is no loss. Advantage is that 162 build directory object sizes shrink dramatically over a full 163 DEBUG_INFO build and compile times are reduced too. 164 Only works with newer gcc versions. 165 166config DEBUG_INFO_SPLIT 167 bool "Produce split debuginfo in .dwo files" 168 depends on DEBUG_INFO && !FRV 169 help 170 Generate debug info into separate .dwo files. This significantly 171 reduces the build directory size for builds with DEBUG_INFO, 172 because it stores the information only once on disk in .dwo 173 files instead of multiple times in object files and executables. 174 In addition the debug information is also compressed. 175 176 Requires recent gcc (4.7+) and recent gdb/binutils. 177 Any tool that packages or reads debug information would need 178 to know about the .dwo files and include them. 179 Incompatible with older versions of ccache. 180 181config DEBUG_INFO_DWARF4 182 bool "Generate dwarf4 debuginfo" 183 depends on DEBUG_INFO 184 help 185 Generate dwarf4 debug info. This requires recent versions 186 of gcc and gdb. It makes the debug information larger. 187 But it significantly improves the success of resolving 188 variables in gdb on optimized code. 189 190config GDB_SCRIPTS 191 bool "Provide GDB scripts for kernel debugging" 192 depends on DEBUG_INFO 193 help 194 This creates the required links to GDB helper scripts in the 195 build directory. If you load vmlinux into gdb, the helper 196 scripts will be automatically imported by gdb as well, and 197 additional functions are available to analyze a Linux kernel 198 instance. See Documentation/dev-tools/gdb-kernel-debugging.rst 199 for further details. 200 201config ENABLE_WARN_DEPRECATED 202 bool "Enable __deprecated logic" 203 default y 204 help 205 Enable the __deprecated logic in the kernel build. 206 Disable this to suppress the "warning: 'foo' is deprecated 207 (declared at kernel/power/somefile.c:1234)" messages. 208 209config ENABLE_MUST_CHECK 210 bool "Enable __must_check logic" 211 default y 212 help 213 Enable the __must_check logic in the kernel build. Disable this to 214 suppress the "warning: ignoring return value of 'foo', declared with 215 attribute warn_unused_result" messages. 216 217config FRAME_WARN 218 int "Warn for stack frames larger than (needs gcc 4.4)" 219 range 0 8192 220 default 0 if KASAN 221 default 2048 if GCC_PLUGIN_LATENT_ENTROPY 222 default 1280 if (!64BIT && PARISC) 223 default 1024 if (!64BIT && !PARISC) 224 default 2048 if 64BIT 225 help 226 Tell gcc to warn at build time for stack frames larger than this. 227 Setting this too low will cause a lot of warnings. 228 Setting it to 0 disables the warning. 229 Requires gcc 4.4 230 231config STRIP_ASM_SYMS 232 bool "Strip assembler-generated symbols during link" 233 default n 234 help 235 Strip internal assembler-generated symbols during a link (symbols 236 that look like '.Lxxx') so they don't pollute the output of 237 get_wchan() and suchlike. 238 239config READABLE_ASM 240 bool "Generate readable assembler code" 241 depends on DEBUG_KERNEL 242 help 243 Disable some compiler optimizations that tend to generate human unreadable 244 assembler output. This may make the kernel slightly slower, but it helps 245 to keep kernel developers who have to stare a lot at assembler listings 246 sane. 247 248config UNUSED_SYMBOLS 249 bool "Enable unused/obsolete exported symbols" 250 default y if X86 251 help 252 Unused but exported symbols make the kernel needlessly bigger. For 253 that reason most of these unused exports will soon be removed. This 254 option is provided temporarily to provide a transition period in case 255 some external kernel module needs one of these symbols anyway. If you 256 encounter such a case in your module, consider if you are actually 257 using the right API. (rationale: since nobody in the kernel is using 258 this in a module, there is a pretty good chance it's actually the 259 wrong interface to use). If you really need the symbol, please send a 260 mail to the linux kernel mailing list mentioning the symbol and why 261 you really need it, and what the merge plan to the mainline kernel for 262 your module is. 263 264config PAGE_OWNER 265 bool "Track page owner" 266 depends on DEBUG_KERNEL && STACKTRACE_SUPPORT 267 select DEBUG_FS 268 select STACKTRACE 269 select STACKDEPOT 270 select PAGE_EXTENSION 271 help 272 This keeps track of what call chain is the owner of a page, may 273 help to find bare alloc_page(s) leaks. Even if you include this 274 feature on your build, it is disabled in default. You should pass 275 "page_owner=on" to boot parameter in order to enable it. Eats 276 a fair amount of memory if enabled. See tools/vm/page_owner_sort.c 277 for user-space helper. 278 279 If unsure, say N. 280 281config DEBUG_FS 282 bool "Debug Filesystem" 283 select SRCU 284 help 285 debugfs is a virtual file system that kernel developers use to put 286 debugging files into. Enable this option to be able to read and 287 write to these files. 288 289 For detailed documentation on the debugfs API, see 290 Documentation/filesystems/. 291 292 If unsure, say N. 293 294config HEADERS_CHECK 295 bool "Run 'make headers_check' when building vmlinux" 296 depends on !UML 297 help 298 This option will extract the user-visible kernel headers whenever 299 building the kernel, and will run basic sanity checks on them to 300 ensure that exported files do not attempt to include files which 301 were not exported, etc. 302 303 If you're making modifications to header files which are 304 relevant for userspace, say 'Y', and check the headers 305 exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in 306 your build tree), to make sure they're suitable. 307 308config DEBUG_SECTION_MISMATCH 309 bool "Enable full Section mismatch analysis" 310 help 311 The section mismatch analysis checks if there are illegal 312 references from one section to another section. 313 During linktime or runtime, some sections are dropped; 314 any use of code/data previously in these sections would 315 most likely result in an oops. 316 In the code, functions and variables are annotated with 317 __init,, etc. (see the full list in include/linux/init.h), 318 which results in the code/data being placed in specific sections. 319 The section mismatch analysis is always performed after a full 320 kernel build, and enabling this option causes the following 321 additional steps to occur: 322 - Add the option -fno-inline-functions-called-once to gcc commands. 323 When inlining a function annotated with __init in a non-init 324 function, we would lose the section information and thus 325 the analysis would not catch the illegal reference. 326 This option tells gcc to inline less (but it does result in 327 a larger kernel). 328 - Run the section mismatch analysis for each module/built-in.o file. 329 When we run the section mismatch analysis on vmlinux.o, we 330 lose valuable information about where the mismatch was 331 introduced. 332 Running the analysis for each module/built-in.o file 333 tells where the mismatch happens much closer to the 334 source. The drawback is that the same mismatch is 335 reported at least twice. 336 - Enable verbose reporting from modpost in order to help resolve 337 the section mismatches that are reported. 338 339config SECTION_MISMATCH_WARN_ONLY 340 bool "Make section mismatch errors non-fatal" 341 default y 342 help 343 If you say N here, the build process will fail if there are any 344 section mismatch, instead of just throwing warnings. 345 346 If unsure, say Y. 347 348# 349# Select this config option from the architecture Kconfig, if it 350# is preferred to always offer frame pointers as a config 351# option on the architecture (regardless of KERNEL_DEBUG): 352# 353config ARCH_WANT_FRAME_POINTERS 354 bool 355 help 356 357config FRAME_POINTER 358 bool "Compile the kernel with frame pointers" 359 depends on DEBUG_KERNEL && \ 360 (CRIS || M68K || FRV || UML || \ 361 SUPERH || BLACKFIN || MN10300 || METAG) || \ 362 ARCH_WANT_FRAME_POINTERS 363 default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS 364 help 365 If you say Y here the resulting kernel image will be slightly 366 larger and slower, but it gives very useful debugging information 367 in case of kernel bugs. (precise oopses/stacktraces/warnings) 368 369config STACK_VALIDATION 370 bool "Compile-time stack metadata validation" 371 depends on HAVE_STACK_VALIDATION 372 default n 373 help 374 Add compile-time checks to validate stack metadata, including frame 375 pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure 376 that runtime stack traces are more reliable. 377 378 This is also a prerequisite for generation of ORC unwind data, which 379 is needed for CONFIG_ORC_UNWINDER. 380 381 For more information, see 382 tools/objtool/Documentation/stack-validation.txt. 383 384config DEBUG_FORCE_WEAK_PER_CPU 385 bool "Force weak per-cpu definitions" 386 depends on DEBUG_KERNEL 387 help 388 s390 and alpha require percpu variables in modules to be 389 defined weak to work around addressing range issue which 390 puts the following two restrictions on percpu variable 391 definitions. 392 393 1. percpu symbols must be unique whether static or not 394 2. percpu variables can't be defined inside a function 395 396 To ensure that generic code follows the above rules, this 397 option forces all percpu variables to be defined as weak. 398 399endmenu # "Compiler options" 400 401config MAGIC_SYSRQ 402 bool "Magic SysRq key" 403 depends on !UML 404 help 405 If you say Y here, you will have some control over the system even 406 if the system crashes for example during kernel debugging (e.g., you 407 will be able to flush the buffer cache to disk, reboot the system 408 immediately or dump some status information). This is accomplished 409 by pressing various keys while holding SysRq (Alt+PrintScreen). It 410 also works on a serial console (on PC hardware at least), if you 411 send a BREAK and then within 5 seconds a command keypress. The 412 keys are documented in <file:Documentation/admin-guide/sysrq.rst>. 413 Don't say Y unless you really know what this hack does. 414 415config MAGIC_SYSRQ_DEFAULT_ENABLE 416 hex "Enable magic SysRq key functions by default" 417 depends on MAGIC_SYSRQ 418 default 0x1 419 help 420 Specifies which SysRq key functions are enabled by default. 421 This may be set to 1 or 0 to enable or disable them all, or 422 to a bitmask as described in Documentation/admin-guide/sysrq.rst. 423 424config MAGIC_SYSRQ_SERIAL 425 bool "Enable magic SysRq key over serial" 426 depends on MAGIC_SYSRQ 427 default y 428 help 429 Many embedded boards have a disconnected TTL level serial which can 430 generate some garbage that can lead to spurious false sysrq detects. 431 This option allows you to decide whether you want to enable the 432 magic SysRq key. 433 434config DEBUG_KERNEL 435 bool "Kernel debugging" 436 help 437 Say Y here if you are developing drivers or trying to debug and 438 identify kernel problems. 439 440menu "Memory Debugging" 441 442source mm/Kconfig.debug 443 444config DEBUG_OBJECTS 445 bool "Debug object operations" 446 depends on DEBUG_KERNEL 447 help 448 If you say Y here, additional code will be inserted into the 449 kernel to track the life time of various objects and validate 450 the operations on those objects. 451 452config DEBUG_OBJECTS_SELFTEST 453 bool "Debug objects selftest" 454 depends on DEBUG_OBJECTS 455 help 456 This enables the selftest of the object debug code. 457 458config DEBUG_OBJECTS_FREE 459 bool "Debug objects in freed memory" 460 depends on DEBUG_OBJECTS 461 help 462 This enables checks whether a k/v free operation frees an area 463 which contains an object which has not been deactivated 464 properly. This can make kmalloc/kfree-intensive workloads 465 much slower. 466 467config DEBUG_OBJECTS_TIMERS 468 bool "Debug timer objects" 469 depends on DEBUG_OBJECTS 470 help 471 If you say Y here, additional code will be inserted into the 472 timer routines to track the life time of timer objects and 473 validate the timer operations. 474 475config DEBUG_OBJECTS_WORK 476 bool "Debug work objects" 477 depends on DEBUG_OBJECTS 478 help 479 If you say Y here, additional code will be inserted into the 480 work queue routines to track the life time of work objects and 481 validate the work operations. 482 483config DEBUG_OBJECTS_RCU_HEAD 484 bool "Debug RCU callbacks objects" 485 depends on DEBUG_OBJECTS 486 help 487 Enable this to turn on debugging of RCU list heads (call_rcu() usage). 488 489config DEBUG_OBJECTS_PERCPU_COUNTER 490 bool "Debug percpu counter objects" 491 depends on DEBUG_OBJECTS 492 help 493 If you say Y here, additional code will be inserted into the 494 percpu counter routines to track the life time of percpu counter 495 objects and validate the percpu counter operations. 496 497config DEBUG_OBJECTS_ENABLE_DEFAULT 498 int "debug_objects bootup default value (0-1)" 499 range 0 1 500 default "1" 501 depends on DEBUG_OBJECTS 502 help 503 Debug objects boot parameter default value 504 505config DEBUG_SLAB 506 bool "Debug slab memory allocations" 507 depends on DEBUG_KERNEL && SLAB && !KMEMCHECK 508 help 509 Say Y here to have the kernel do limited verification on memory 510 allocation as well as poisoning memory on free to catch use of freed 511 memory. This can make kmalloc/kfree-intensive workloads much slower. 512 513config DEBUG_SLAB_LEAK 514 bool "Memory leak debugging" 515 depends on DEBUG_SLAB 516 517config SLUB_DEBUG_ON 518 bool "SLUB debugging on by default" 519 depends on SLUB && SLUB_DEBUG && !KMEMCHECK 520 default n 521 help 522 Boot with debugging on by default. SLUB boots by default with 523 the runtime debug capabilities switched off. Enabling this is 524 equivalent to specifying the "slub_debug" parameter on boot. 525 There is no support for more fine grained debug control like 526 possible with slub_debug=xxx. SLUB debugging may be switched 527 off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying 528 "slub_debug=-". 529 530config SLUB_STATS 531 default n 532 bool "Enable SLUB performance statistics" 533 depends on SLUB && SYSFS 534 help 535 SLUB statistics are useful to debug SLUBs allocation behavior in 536 order find ways to optimize the allocator. This should never be 537 enabled for production use since keeping statistics slows down 538 the allocator by a few percentage points. The slabinfo command 539 supports the determination of the most active slabs to figure 540 out which slabs are relevant to a particular load. 541 Try running: slabinfo -DA 542 543config HAVE_DEBUG_KMEMLEAK 544 bool 545 546config DEBUG_KMEMLEAK 547 bool "Kernel memory leak detector" 548 depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK 549 select DEBUG_FS 550 select STACKTRACE if STACKTRACE_SUPPORT 551 select KALLSYMS 552 select CRC32 553 help 554 Say Y here if you want to enable the memory leak 555 detector. The memory allocation/freeing is traced in a way 556 similar to the Boehm's conservative garbage collector, the 557 difference being that the orphan objects are not freed but 558 only shown in /sys/kernel/debug/kmemleak. Enabling this 559 feature will introduce an overhead to memory 560 allocations. See Documentation/dev-tools/kmemleak.rst for more 561 details. 562 563 Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances 564 of finding leaks due to the slab objects poisoning. 565 566 In order to access the kmemleak file, debugfs needs to be 567 mounted (usually at /sys/kernel/debug). 568 569config DEBUG_KMEMLEAK_EARLY_LOG_SIZE 570 int "Maximum kmemleak early log entries" 571 depends on DEBUG_KMEMLEAK 572 range 200 40000 573 default 400 574 help 575 Kmemleak must track all the memory allocations to avoid 576 reporting false positives. Since memory may be allocated or 577 freed before kmemleak is initialised, an early log buffer is 578 used to store these actions. If kmemleak reports "early log 579 buffer exceeded", please increase this value. 580 581config DEBUG_KMEMLEAK_TEST 582 tristate "Simple test for the kernel memory leak detector" 583 depends on DEBUG_KMEMLEAK && m 584 help 585 This option enables a module that explicitly leaks memory. 586 587 If unsure, say N. 588 589config DEBUG_KMEMLEAK_DEFAULT_OFF 590 bool "Default kmemleak to off" 591 depends on DEBUG_KMEMLEAK 592 help 593 Say Y here to disable kmemleak by default. It can then be enabled 594 on the command line via kmemleak=on. 595 596config DEBUG_STACK_USAGE 597 bool "Stack utilization instrumentation" 598 depends on DEBUG_KERNEL && !IA64 599 help 600 Enables the display of the minimum amount of free stack which each 601 task has ever had available in the sysrq-T and sysrq-P debug output. 602 603 This option will slow down process creation somewhat. 604 605config DEBUG_VM 606 bool "Debug VM" 607 depends on DEBUG_KERNEL 608 help 609 Enable this to turn on extended checks in the virtual-memory system 610 that may impact performance. 611 612 If unsure, say N. 613 614config DEBUG_VM_VMACACHE 615 bool "Debug VMA caching" 616 depends on DEBUG_VM 617 help 618 Enable this to turn on VMA caching debug information. Doing so 619 can cause significant overhead, so only enable it in non-production 620 environments. 621 622 If unsure, say N. 623 624config DEBUG_VM_RB 625 bool "Debug VM red-black trees" 626 depends on DEBUG_VM 627 help 628 Enable VM red-black tree debugging information and extra validations. 629 630 If unsure, say N. 631 632config DEBUG_VM_PGFLAGS 633 bool "Debug page-flags operations" 634 depends on DEBUG_VM 635 help 636 Enables extra validation on page flags operations. 637 638 If unsure, say N. 639 640config ARCH_HAS_DEBUG_VIRTUAL 641 bool 642 643config DEBUG_VIRTUAL 644 bool "Debug VM translations" 645 depends on DEBUG_KERNEL && ARCH_HAS_DEBUG_VIRTUAL 646 help 647 Enable some costly sanity checks in virtual to page code. This can 648 catch mistakes with virt_to_page() and friends. 649 650 If unsure, say N. 651 652config DEBUG_NOMMU_REGIONS 653 bool "Debug the global anon/private NOMMU mapping region tree" 654 depends on DEBUG_KERNEL && !MMU 655 help 656 This option causes the global tree of anonymous and private mapping 657 regions to be regularly checked for invalid topology. 658 659config DEBUG_MEMORY_INIT 660 bool "Debug memory initialisation" if EXPERT 661 default !EXPERT 662 help 663 Enable this for additional checks during memory initialisation. 664 The sanity checks verify aspects of the VM such as the memory model 665 and other information provided by the architecture. Verbose 666 information will be printed at KERN_DEBUG loglevel depending 667 on the mminit_loglevel= command-line option. 668 669 If unsure, say Y 670 671config MEMORY_NOTIFIER_ERROR_INJECT 672 tristate "Memory hotplug notifier error injection module" 673 depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION 674 help 675 This option provides the ability to inject artificial errors to 676 memory hotplug notifier chain callbacks. It is controlled through 677 debugfs interface under /sys/kernel/debug/notifier-error-inject/memory 678 679 If the notifier call chain should be failed with some events 680 notified, write the error code to "actions/<notifier event>/error". 681 682 Example: Inject memory hotplug offline error (-12 == -ENOMEM) 683 684 # cd /sys/kernel/debug/notifier-error-inject/memory 685 # echo -12 > actions/MEM_GOING_OFFLINE/error 686 # echo offline > /sys/devices/system/memory/memoryXXX/state 687 bash: echo: write error: Cannot allocate memory 688 689 To compile this code as a module, choose M here: the module will 690 be called memory-notifier-error-inject. 691 692 If unsure, say N. 693 694config DEBUG_PER_CPU_MAPS 695 bool "Debug access to per_cpu maps" 696 depends on DEBUG_KERNEL 697 depends on SMP 698 help 699 Say Y to verify that the per_cpu map being accessed has 700 been set up. This adds a fair amount of code to kernel memory 701 and decreases performance. 702 703 Say N if unsure. 704 705config DEBUG_HIGHMEM 706 bool "Highmem debugging" 707 depends on DEBUG_KERNEL && HIGHMEM 708 help 709 This option enables additional error checking for high memory 710 systems. Disable for production systems. 711 712config HAVE_DEBUG_STACKOVERFLOW 713 bool 714 715config DEBUG_STACKOVERFLOW 716 bool "Check for stack overflows" 717 depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW 718 ---help--- 719 Say Y here if you want to check for overflows of kernel, IRQ 720 and exception stacks (if your architecture uses them). This 721 option will show detailed messages if free stack space drops 722 below a certain limit. 723 724 These kinds of bugs usually occur when call-chains in the 725 kernel get too deep, especially when interrupts are 726 involved. 727 728 Use this in cases where you see apparently random memory 729 corruption, especially if it appears in 'struct thread_info' 730 731 If in doubt, say "N". 732 733source "lib/Kconfig.kmemcheck" 734 735source "lib/Kconfig.kasan" 736 737endmenu # "Memory Debugging" 738 739config ARCH_HAS_KCOV 740 bool 741 help 742 KCOV does not have any arch-specific code, but currently it is enabled 743 only for x86_64. KCOV requires testing on other archs, and most likely 744 disabling of instrumentation for some early boot code. 745 746config KCOV 747 bool "Code coverage for fuzzing" 748 depends on ARCH_HAS_KCOV 749 select DEBUG_FS 750 select GCC_PLUGINS if !COMPILE_TEST 751 select GCC_PLUGIN_SANCOV if !COMPILE_TEST 752 help 753 KCOV exposes kernel code coverage information in a form suitable 754 for coverage-guided fuzzing (randomized testing). 755 756 If RANDOMIZE_BASE is enabled, PC values will not be stable across 757 different machines and across reboots. If you need stable PC values, 758 disable RANDOMIZE_BASE. 759 760 For more details, see Documentation/dev-tools/kcov.rst. 761 762config KCOV_INSTRUMENT_ALL 763 bool "Instrument all code by default" 764 depends on KCOV 765 default y if KCOV 766 help 767 If you are doing generic system call fuzzing (like e.g. syzkaller), 768 then you will want to instrument the whole kernel and you should 769 say y here. If you are doing more targeted fuzzing (like e.g. 770 filesystem fuzzing with AFL) then you will want to enable coverage 771 for more specific subsets of files, and should say n here. 772 773config DEBUG_SHIRQ 774 bool "Debug shared IRQ handlers" 775 depends on DEBUG_KERNEL 776 help 777 Enable this to generate a spurious interrupt as soon as a shared 778 interrupt handler is registered, and just before one is deregistered. 779 Drivers ought to be able to handle interrupts coming in at those 780 points; some don't and need to be caught. 781 782menu "Debug Lockups and Hangs" 783 784config LOCKUP_DETECTOR 785 bool 786 787config SOFTLOCKUP_DETECTOR 788 bool "Detect Soft Lockups" 789 depends on DEBUG_KERNEL && !S390 790 select LOCKUP_DETECTOR 791 help 792 Say Y here to enable the kernel to act as a watchdog to detect 793 soft lockups. 794 795 Softlockups are bugs that cause the kernel to loop in kernel 796 mode for more than 20 seconds, without giving other tasks a 797 chance to run. The current stack trace is displayed upon 798 detection and the system will stay locked up. 799 800config HARDLOCKUP_DETECTOR_PERF 801 bool 802 select SOFTLOCKUP_DETECTOR 803 804# 805# Enables a timestamp based low pass filter to compensate for perf based 806# hard lockup detection which runs too fast due to turbo modes. 807# 808config HARDLOCKUP_CHECK_TIMESTAMP 809 bool 810 811# 812# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard 813# lockup detector rather than the perf based detector. 814# 815config HARDLOCKUP_DETECTOR 816 bool "Detect Hard Lockups" 817 depends on DEBUG_KERNEL && !S390 818 depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_ARCH 819 select LOCKUP_DETECTOR 820 select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF 821 select HARDLOCKUP_DETECTOR_ARCH if HAVE_HARDLOCKUP_DETECTOR_ARCH 822 help 823 Say Y here to enable the kernel to act as a watchdog to detect 824 hard lockups. 825 826 Hardlockups are bugs that cause the CPU to loop in kernel mode 827 for more than 10 seconds, without letting other interrupts have a 828 chance to run. The current stack trace is displayed upon detection 829 and the system will stay locked up. 830 831config BOOTPARAM_HARDLOCKUP_PANIC 832 bool "Panic (Reboot) On Hard Lockups" 833 depends on HARDLOCKUP_DETECTOR 834 help 835 Say Y here to enable the kernel to panic on "hard lockups", 836 which are bugs that cause the kernel to loop in kernel 837 mode with interrupts disabled for more than 10 seconds (configurable 838 using the watchdog_thresh sysctl). 839 840 Say N if unsure. 841 842config BOOTPARAM_HARDLOCKUP_PANIC_VALUE 843 int 844 depends on HARDLOCKUP_DETECTOR 845 range 0 1 846 default 0 if !BOOTPARAM_HARDLOCKUP_PANIC 847 default 1 if BOOTPARAM_HARDLOCKUP_PANIC 848 849config BOOTPARAM_SOFTLOCKUP_PANIC 850 bool "Panic (Reboot) On Soft Lockups" 851 depends on SOFTLOCKUP_DETECTOR 852 help 853 Say Y here to enable the kernel to panic on "soft lockups", 854 which are bugs that cause the kernel to loop in kernel 855 mode for more than 20 seconds (configurable using the watchdog_thresh 856 sysctl), without giving other tasks a chance to run. 857 858 The panic can be used in combination with panic_timeout, 859 to cause the system to reboot automatically after a 860 lockup has been detected. This feature is useful for 861 high-availability systems that have uptime guarantees and 862 where a lockup must be resolved ASAP. 863 864 Say N if unsure. 865 866config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE 867 int 868 depends on SOFTLOCKUP_DETECTOR 869 range 0 1 870 default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC 871 default 1 if BOOTPARAM_SOFTLOCKUP_PANIC 872 873config DETECT_HUNG_TASK 874 bool "Detect Hung Tasks" 875 depends on DEBUG_KERNEL 876 default SOFTLOCKUP_DETECTOR 877 help 878 Say Y here to enable the kernel to detect "hung tasks", 879 which are bugs that cause the task to be stuck in 880 uninterruptible "D" state indefinitely. 881 882 When a hung task is detected, the kernel will print the 883 current stack trace (which you should report), but the 884 task will stay in uninterruptible state. If lockdep is 885 enabled then all held locks will also be reported. This 886 feature has negligible overhead. 887 888config DEFAULT_HUNG_TASK_TIMEOUT 889 int "Default timeout for hung task detection (in seconds)" 890 depends on DETECT_HUNG_TASK 891 default 120 892 help 893 This option controls the default timeout (in seconds) used 894 to determine when a task has become non-responsive and should 895 be considered hung. 896 897 It can be adjusted at runtime via the kernel.hung_task_timeout_secs 898 sysctl or by writing a value to 899 /proc/sys/kernel/hung_task_timeout_secs. 900 901 A timeout of 0 disables the check. The default is two minutes. 902 Keeping the default should be fine in most cases. 903 904config BOOTPARAM_HUNG_TASK_PANIC 905 bool "Panic (Reboot) On Hung Tasks" 906 depends on DETECT_HUNG_TASK 907 help 908 Say Y here to enable the kernel to panic on "hung tasks", 909 which are bugs that cause the kernel to leave a task stuck 910 in uninterruptible "D" state. 911 912 The panic can be used in combination with panic_timeout, 913 to cause the system to reboot automatically after a 914 hung task has been detected. This feature is useful for 915 high-availability systems that have uptime guarantees and 916 where a hung tasks must be resolved ASAP. 917 918 Say N if unsure. 919 920config BOOTPARAM_HUNG_TASK_PANIC_VALUE 921 int 922 depends on DETECT_HUNG_TASK 923 range 0 1 924 default 0 if !BOOTPARAM_HUNG_TASK_PANIC 925 default 1 if BOOTPARAM_HUNG_TASK_PANIC 926 927config WQ_WATCHDOG 928 bool "Detect Workqueue Stalls" 929 depends on DEBUG_KERNEL 930 help 931 Say Y here to enable stall detection on workqueues. If a 932 worker pool doesn't make forward progress on a pending work 933 item for over a given amount of time, 30s by default, a 934 warning message is printed along with dump of workqueue 935 state. This can be configured through kernel parameter 936 "workqueue.watchdog_thresh" and its sysfs counterpart. 937 938endmenu # "Debug lockups and hangs" 939 940config PANIC_ON_OOPS 941 bool "Panic on Oops" 942 help 943 Say Y here to enable the kernel to panic when it oopses. This 944 has the same effect as setting oops=panic on the kernel command 945 line. 946 947 This feature is useful to ensure that the kernel does not do 948 anything erroneous after an oops which could result in data 949 corruption or other issues. 950 951 Say N if unsure. 952 953config PANIC_ON_OOPS_VALUE 954 int 955 range 0 1 956 default 0 if !PANIC_ON_OOPS 957 default 1 if PANIC_ON_OOPS 958 959config PANIC_TIMEOUT 960 int "panic timeout" 961 default 0 962 help 963 Set the timeout value (in seconds) until a reboot occurs when the 964 the kernel panics. If n = 0, then we wait forever. A timeout 965 value n > 0 will wait n seconds before rebooting, while a timeout 966 value n < 0 will reboot immediately. 967 968config SCHED_DEBUG 969 bool "Collect scheduler debugging info" 970 depends on DEBUG_KERNEL && PROC_FS 971 default y 972 help 973 If you say Y here, the /proc/sched_debug file will be provided 974 that can help debug the scheduler. The runtime overhead of this 975 option is minimal. 976 977config SCHED_INFO 978 bool 979 default n 980 981config SCHEDSTATS 982 bool "Collect scheduler statistics" 983 depends on DEBUG_KERNEL && PROC_FS 984 select SCHED_INFO 985 help 986 If you say Y here, additional code will be inserted into the 987 scheduler and related routines to collect statistics about 988 scheduler behavior and provide them in /proc/schedstat. These 989 stats may be useful for both tuning and debugging the scheduler 990 If you aren't debugging the scheduler or trying to tune a specific 991 application, you can say N to avoid the very slight overhead 992 this adds. 993 994config SCHED_STACK_END_CHECK 995 bool "Detect stack corruption on calls to schedule()" 996 depends on DEBUG_KERNEL 997 default n 998 help 999 This option checks for a stack overrun on calls to schedule(). 1000 If the stack end location is found to be over written always panic as 1001 the content of the corrupted region can no longer be trusted. 1002 This is to ensure no erroneous behaviour occurs which could result in 1003 data corruption or a sporadic crash at a later stage once the region 1004 is examined. The runtime overhead introduced is minimal. 1005 1006config DEBUG_TIMEKEEPING 1007 bool "Enable extra timekeeping sanity checking" 1008 help 1009 This option will enable additional timekeeping sanity checks 1010 which may be helpful when diagnosing issues where timekeeping 1011 problems are suspected. 1012 1013 This may include checks in the timekeeping hotpaths, so this 1014 option may have a (very small) performance impact to some 1015 workloads. 1016 1017 If unsure, say N. 1018 1019config DEBUG_PREEMPT 1020 bool "Debug preemptible kernel" 1021 depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT 1022 default y 1023 help 1024 If you say Y here then the kernel will use a debug variant of the 1025 commonly used smp_processor_id() function and will print warnings 1026 if kernel code uses it in a preemption-unsafe way. Also, the kernel 1027 will detect preemption count underflows. 1028 1029menu "Lock Debugging (spinlocks, mutexes, etc...)" 1030 1031config DEBUG_RT_MUTEXES 1032 bool "RT Mutex debugging, deadlock detection" 1033 depends on DEBUG_KERNEL && RT_MUTEXES 1034 help 1035 This allows rt mutex semantics violations and rt mutex related 1036 deadlocks (lockups) to be detected and reported automatically. 1037 1038config DEBUG_SPINLOCK 1039 bool "Spinlock and rw-lock debugging: basic checks" 1040 depends on DEBUG_KERNEL 1041 select UNINLINE_SPIN_UNLOCK 1042 help 1043 Say Y here and build SMP to catch missing spinlock initialization 1044 and certain other kinds of spinlock errors commonly made. This is 1045 best used in conjunction with the NMI watchdog so that spinlock 1046 deadlocks are also debuggable. 1047 1048config DEBUG_MUTEXES 1049 bool "Mutex debugging: basic checks" 1050 depends on DEBUG_KERNEL 1051 help 1052 This feature allows mutex semantics violations to be detected and 1053 reported. 1054 1055config DEBUG_WW_MUTEX_SLOWPATH 1056 bool "Wait/wound mutex debugging: Slowpath testing" 1057 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1058 select DEBUG_LOCK_ALLOC 1059 select DEBUG_SPINLOCK 1060 select DEBUG_MUTEXES 1061 help 1062 This feature enables slowpath testing for w/w mutex users by 1063 injecting additional -EDEADLK wound/backoff cases. Together with 1064 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this 1065 will test all possible w/w mutex interface abuse with the 1066 exception of simply not acquiring all the required locks. 1067 Note that this feature can introduce significant overhead, so 1068 it really should not be enabled in a production or distro kernel, 1069 even a debug kernel. If you are a driver writer, enable it. If 1070 you are a distro, do not. 1071 1072config DEBUG_LOCK_ALLOC 1073 bool "Lock debugging: detect incorrect freeing of live locks" 1074 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1075 select DEBUG_SPINLOCK 1076 select DEBUG_MUTEXES 1077 select DEBUG_RT_MUTEXES if RT_MUTEXES 1078 select LOCKDEP 1079 help 1080 This feature will check whether any held lock (spinlock, rwlock, 1081 mutex or rwsem) is incorrectly freed by the kernel, via any of the 1082 memory-freeing routines (kfree(), kmem_cache_free(), free_pages(), 1083 vfree(), etc.), whether a live lock is incorrectly reinitialized via 1084 spin_lock_init()/mutex_init()/etc., or whether there is any lock 1085 held during task exit. 1086 1087config PROVE_LOCKING 1088 bool "Lock debugging: prove locking correctness" 1089 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1090 select LOCKDEP 1091 select DEBUG_SPINLOCK 1092 select DEBUG_MUTEXES 1093 select DEBUG_RT_MUTEXES if RT_MUTEXES 1094 select DEBUG_LOCK_ALLOC 1095 select LOCKDEP_CROSSRELEASE if BROKEN 1096 select LOCKDEP_COMPLETIONS if BROKEN 1097 select TRACE_IRQFLAGS 1098 default n 1099 help 1100 This feature enables the kernel to prove that all locking 1101 that occurs in the kernel runtime is mathematically 1102 correct: that under no circumstance could an arbitrary (and 1103 not yet triggered) combination of observed locking 1104 sequences (on an arbitrary number of CPUs, running an 1105 arbitrary number of tasks and interrupt contexts) cause a 1106 deadlock. 1107 1108 In short, this feature enables the kernel to report locking 1109 related deadlocks before they actually occur. 1110 1111 The proof does not depend on how hard and complex a 1112 deadlock scenario would be to trigger: how many 1113 participant CPUs, tasks and irq-contexts would be needed 1114 for it to trigger. The proof also does not depend on 1115 timing: if a race and a resulting deadlock is possible 1116 theoretically (no matter how unlikely the race scenario 1117 is), it will be proven so and will immediately be 1118 reported by the kernel (once the event is observed that 1119 makes the deadlock theoretically possible). 1120 1121 If a deadlock is impossible (i.e. the locking rules, as 1122 observed by the kernel, are mathematically correct), the 1123 kernel reports nothing. 1124 1125 NOTE: this feature can also be enabled for rwlocks, mutexes 1126 and rwsems - in which case all dependencies between these 1127 different locking variants are observed and mapped too, and 1128 the proof of observed correctness is also maintained for an 1129 arbitrary combination of these separate locking variants. 1130 1131 For more details, see Documentation/locking/lockdep-design.txt. 1132 1133config LOCKDEP 1134 bool 1135 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1136 select STACKTRACE 1137 select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE && !X86 1138 select KALLSYMS 1139 select KALLSYMS_ALL 1140 1141config LOCKDEP_SMALL 1142 bool 1143 1144config LOCK_STAT 1145 bool "Lock usage statistics" 1146 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1147 select LOCKDEP 1148 select DEBUG_SPINLOCK 1149 select DEBUG_MUTEXES 1150 select DEBUG_RT_MUTEXES if RT_MUTEXES 1151 select DEBUG_LOCK_ALLOC 1152 default n 1153 help 1154 This feature enables tracking lock contention points 1155 1156 For more details, see Documentation/locking/lockstat.txt 1157 1158 This also enables lock events required by "perf lock", 1159 subcommand of perf. 1160 If you want to use "perf lock", you also need to turn on 1161 CONFIG_EVENT_TRACING. 1162 1163 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. 1164 (CONFIG_LOCKDEP defines "acquire" and "release" events.) 1165 1166config LOCKDEP_CROSSRELEASE 1167 bool 1168 help 1169 This makes lockdep work for crosslock which is a lock allowed to 1170 be released in a different context from the acquisition context. 1171 Normally a lock must be released in the context acquiring the lock. 1172 However, relexing this constraint helps synchronization primitives 1173 such as page locks or completions can use the lock correctness 1174 detector, lockdep. 1175 1176config LOCKDEP_COMPLETIONS 1177 bool 1178 help 1179 A deadlock caused by wait_for_completion() and complete() can be 1180 detected by lockdep using crossrelease feature. 1181 1182config DEBUG_LOCKDEP 1183 bool "Lock dependency engine debugging" 1184 depends on DEBUG_KERNEL && LOCKDEP 1185 help 1186 If you say Y here, the lock dependency engine will do 1187 additional runtime checks to debug itself, at the price 1188 of more runtime overhead. 1189 1190config DEBUG_ATOMIC_SLEEP 1191 bool "Sleep inside atomic section checking" 1192 select PREEMPT_COUNT 1193 depends on DEBUG_KERNEL 1194 help 1195 If you say Y here, various routines which may sleep will become very 1196 noisy if they are called inside atomic sections: when a spinlock is 1197 held, inside an rcu read side critical section, inside preempt disabled 1198 sections, inside an interrupt, etc... 1199 1200config DEBUG_LOCKING_API_SELFTESTS 1201 bool "Locking API boot-time self-tests" 1202 depends on DEBUG_KERNEL 1203 help 1204 Say Y here if you want the kernel to run a short self-test during 1205 bootup. The self-test checks whether common types of locking bugs 1206 are detected by debugging mechanisms or not. (if you disable 1207 lock debugging then those bugs wont be detected of course.) 1208 The following locking APIs are covered: spinlocks, rwlocks, 1209 mutexes and rwsems. 1210 1211config LOCK_TORTURE_TEST 1212 tristate "torture tests for locking" 1213 depends on DEBUG_KERNEL 1214 select TORTURE_TEST 1215 default n 1216 help 1217 This option provides a kernel module that runs torture tests 1218 on kernel locking primitives. The kernel module may be built 1219 after the fact on the running kernel to be tested, if desired. 1220 1221 Say Y here if you want kernel locking-primitive torture tests 1222 to be built into the kernel. 1223 Say M if you want these torture tests to build as a module. 1224 Say N if you are unsure. 1225 1226config WW_MUTEX_SELFTEST 1227 tristate "Wait/wound mutex selftests" 1228 help 1229 This option provides a kernel module that runs tests on the 1230 on the struct ww_mutex locking API. 1231 1232 It is recommended to enable DEBUG_WW_MUTEX_SLOWPATH in conjunction 1233 with this test harness. 1234 1235 Say M if you want these self tests to build as a module. 1236 Say N if you are unsure. 1237 1238endmenu # lock debugging 1239 1240config TRACE_IRQFLAGS 1241 bool 1242 help 1243 Enables hooks to interrupt enabling and disabling for 1244 either tracing or lock debugging. 1245 1246config STACKTRACE 1247 bool "Stack backtrace support" 1248 depends on STACKTRACE_SUPPORT 1249 help 1250 This option causes the kernel to create a /proc/pid/stack for 1251 every process, showing its current stack trace. 1252 It is also used by various kernel debugging features that require 1253 stack trace generation. 1254 1255config WARN_ALL_UNSEEDED_RANDOM 1256 bool "Warn for all uses of unseeded randomness" 1257 default n 1258 help 1259 Some parts of the kernel contain bugs relating to their use of 1260 cryptographically secure random numbers before it's actually possible 1261 to generate those numbers securely. This setting ensures that these 1262 flaws don't go unnoticed, by enabling a message, should this ever 1263 occur. This will allow people with obscure setups to know when things 1264 are going wrong, so that they might contact developers about fixing 1265 it. 1266 1267 Unfortunately, on some models of some architectures getting 1268 a fully seeded CRNG is extremely difficult, and so this can 1269 result in dmesg getting spammed for a surprisingly long 1270 time. This is really bad from a security perspective, and 1271 so architecture maintainers really need to do what they can 1272 to get the CRNG seeded sooner after the system is booted. 1273 However, since users can not do anything actionble to 1274 address this, by default the kernel will issue only a single 1275 warning for the first use of unseeded randomness. 1276 1277 Say Y here if you want to receive warnings for all uses of 1278 unseeded randomness. This will be of use primarily for 1279 those developers interersted in improving the security of 1280 Linux kernels running on their architecture (or 1281 subarchitecture). 1282 1283config DEBUG_KOBJECT 1284 bool "kobject debugging" 1285 depends on DEBUG_KERNEL 1286 help 1287 If you say Y here, some extra kobject debugging messages will be sent 1288 to the syslog. 1289 1290config DEBUG_KOBJECT_RELEASE 1291 bool "kobject release debugging" 1292 depends on DEBUG_OBJECTS_TIMERS 1293 help 1294 kobjects are reference counted objects. This means that their 1295 last reference count put is not predictable, and the kobject can 1296 live on past the point at which a driver decides to drop it's 1297 initial reference to the kobject gained on allocation. An 1298 example of this would be a struct device which has just been 1299 unregistered. 1300 1301 However, some buggy drivers assume that after such an operation, 1302 the memory backing the kobject can be immediately freed. This 1303 goes completely against the principles of a refcounted object. 1304 1305 If you say Y here, the kernel will delay the release of kobjects 1306 on the last reference count to improve the visibility of this 1307 kind of kobject release bug. 1308 1309config HAVE_DEBUG_BUGVERBOSE 1310 bool 1311 1312config DEBUG_BUGVERBOSE 1313 bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT 1314 depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE) 1315 default y 1316 help 1317 Say Y here to make BUG() panics output the file name and line number 1318 of the BUG call as well as the EIP and oops trace. This aids 1319 debugging but costs about 70-100K of memory. 1320 1321config DEBUG_LIST 1322 bool "Debug linked list manipulation" 1323 depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION 1324 help 1325 Enable this to turn on extended checks in the linked-list 1326 walking routines. 1327 1328 If unsure, say N. 1329 1330config DEBUG_PI_LIST 1331 bool "Debug priority linked list manipulation" 1332 depends on DEBUG_KERNEL 1333 help 1334 Enable this to turn on extended checks in the priority-ordered 1335 linked-list (plist) walking routines. This checks the entire 1336 list multiple times during each manipulation. 1337 1338 If unsure, say N. 1339 1340config DEBUG_SG 1341 bool "Debug SG table operations" 1342 depends on DEBUG_KERNEL 1343 help 1344 Enable this to turn on checks on scatter-gather tables. This can 1345 help find problems with drivers that do not properly initialize 1346 their sg tables. 1347 1348 If unsure, say N. 1349 1350config DEBUG_NOTIFIERS 1351 bool "Debug notifier call chains" 1352 depends on DEBUG_KERNEL 1353 help 1354 Enable this to turn on sanity checking for notifier call chains. 1355 This is most useful for kernel developers to make sure that 1356 modules properly unregister themselves from notifier chains. 1357 This is a relatively cheap check but if you care about maximum 1358 performance, say N. 1359 1360config DEBUG_CREDENTIALS 1361 bool "Debug credential management" 1362 depends on DEBUG_KERNEL 1363 help 1364 Enable this to turn on some debug checking for credential 1365 management. The additional code keeps track of the number of 1366 pointers from task_structs to any given cred struct, and checks to 1367 see that this number never exceeds the usage count of the cred 1368 struct. 1369 1370 Furthermore, if SELinux is enabled, this also checks that the 1371 security pointer in the cred struct is never seen to be invalid. 1372 1373 If unsure, say N. 1374 1375source "kernel/rcu/Kconfig.debug" 1376 1377config DEBUG_WQ_FORCE_RR_CPU 1378 bool "Force round-robin CPU selection for unbound work items" 1379 depends on DEBUG_KERNEL 1380 default n 1381 help 1382 Workqueue used to implicitly guarantee that work items queued 1383 without explicit CPU specified are put on the local CPU. This 1384 guarantee is no longer true and while local CPU is still 1385 preferred work items may be put on foreign CPUs. Kernel 1386 parameter "workqueue.debug_force_rr_cpu" is added to force 1387 round-robin CPU selection to flush out usages which depend on the 1388 now broken guarantee. This config option enables the debug 1389 feature by default. When enabled, memory and cache locality will 1390 be impacted. 1391 1392config DEBUG_BLOCK_EXT_DEVT 1393 bool "Force extended block device numbers and spread them" 1394 depends on DEBUG_KERNEL 1395 depends on BLOCK 1396 default n 1397 help 1398 BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON 1399 SOME DISTRIBUTIONS. DO NOT ENABLE THIS UNLESS YOU KNOW WHAT 1400 YOU ARE DOING. Distros, please enable this and fix whatever 1401 is broken. 1402 1403 Conventionally, block device numbers are allocated from 1404 predetermined contiguous area. However, extended block area 1405 may introduce non-contiguous block device numbers. This 1406 option forces most block device numbers to be allocated from 1407 the extended space and spreads them to discover kernel or 1408 userland code paths which assume predetermined contiguous 1409 device number allocation. 1410 1411 Note that turning on this debug option shuffles all the 1412 device numbers for all IDE and SCSI devices including libata 1413 ones, so root partition specified using device number 1414 directly (via rdev or root=MAJ:MIN) won't work anymore. 1415 Textual device names (root=/dev/sdXn) will continue to work. 1416 1417 Say N if you are unsure. 1418 1419config CPU_HOTPLUG_STATE_CONTROL 1420 bool "Enable CPU hotplug state control" 1421 depends on DEBUG_KERNEL 1422 depends on HOTPLUG_CPU 1423 default n 1424 help 1425 Allows to write steps between "offline" and "online" to the CPUs 1426 sysfs target file so states can be stepped granular. This is a debug 1427 option for now as the hotplug machinery cannot be stopped and 1428 restarted at arbitrary points yet. 1429 1430 Say N if your are unsure. 1431 1432config NOTIFIER_ERROR_INJECTION 1433 tristate "Notifier error injection" 1434 depends on DEBUG_KERNEL 1435 select DEBUG_FS 1436 help 1437 This option provides the ability to inject artificial errors to 1438 specified notifier chain callbacks. It is useful to test the error 1439 handling of notifier call chain failures. 1440 1441 Say N if unsure. 1442 1443config PM_NOTIFIER_ERROR_INJECT 1444 tristate "PM notifier error injection module" 1445 depends on PM && NOTIFIER_ERROR_INJECTION 1446 default m if PM_DEBUG 1447 help 1448 This option provides the ability to inject artificial errors to 1449 PM notifier chain callbacks. It is controlled through debugfs 1450 interface /sys/kernel/debug/notifier-error-inject/pm 1451 1452 If the notifier call chain should be failed with some events 1453 notified, write the error code to "actions/<notifier event>/error". 1454 1455 Example: Inject PM suspend error (-12 = -ENOMEM) 1456 1457 # cd /sys/kernel/debug/notifier-error-inject/pm/ 1458 # echo -12 > actions/PM_SUSPEND_PREPARE/error 1459 # echo mem > /sys/power/state 1460 bash: echo: write error: Cannot allocate memory 1461 1462 To compile this code as a module, choose M here: the module will 1463 be called pm-notifier-error-inject. 1464 1465 If unsure, say N. 1466 1467config OF_RECONFIG_NOTIFIER_ERROR_INJECT 1468 tristate "OF reconfig notifier error injection module" 1469 depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION 1470 help 1471 This option provides the ability to inject artificial errors to 1472 OF reconfig notifier chain callbacks. It is controlled 1473 through debugfs interface under 1474 /sys/kernel/debug/notifier-error-inject/OF-reconfig/ 1475 1476 If the notifier call chain should be failed with some events 1477 notified, write the error code to "actions/<notifier event>/error". 1478 1479 To compile this code as a module, choose M here: the module will 1480 be called of-reconfig-notifier-error-inject. 1481 1482 If unsure, say N. 1483 1484config NETDEV_NOTIFIER_ERROR_INJECT 1485 tristate "Netdev notifier error injection module" 1486 depends on NET && NOTIFIER_ERROR_INJECTION 1487 help 1488 This option provides the ability to inject artificial errors to 1489 netdevice notifier chain callbacks. It is controlled through debugfs 1490 interface /sys/kernel/debug/notifier-error-inject/netdev 1491 1492 If the notifier call chain should be failed with some events 1493 notified, write the error code to "actions/<notifier event>/error". 1494 1495 Example: Inject netdevice mtu change error (-22 = -EINVAL) 1496 1497 # cd /sys/kernel/debug/notifier-error-inject/netdev 1498 # echo -22 > actions/NETDEV_CHANGEMTU/error 1499 # ip link set eth0 mtu 1024 1500 RTNETLINK answers: Invalid argument 1501 1502 To compile this code as a module, choose M here: the module will 1503 be called netdev-notifier-error-inject. 1504 1505 If unsure, say N. 1506 1507config FAULT_INJECTION 1508 bool "Fault-injection framework" 1509 depends on DEBUG_KERNEL 1510 help 1511 Provide fault-injection framework. 1512 For more details, see Documentation/fault-injection/. 1513 1514config FAILSLAB 1515 bool "Fault-injection capability for kmalloc" 1516 depends on FAULT_INJECTION 1517 depends on SLAB || SLUB 1518 help 1519 Provide fault-injection capability for kmalloc. 1520 1521config FAIL_PAGE_ALLOC 1522 bool "Fault-injection capabilitiy for alloc_pages()" 1523 depends on FAULT_INJECTION 1524 help 1525 Provide fault-injection capability for alloc_pages(). 1526 1527config FAIL_MAKE_REQUEST 1528 bool "Fault-injection capability for disk IO" 1529 depends on FAULT_INJECTION && BLOCK 1530 help 1531 Provide fault-injection capability for disk IO. 1532 1533config FAIL_IO_TIMEOUT 1534 bool "Fault-injection capability for faking disk interrupts" 1535 depends on FAULT_INJECTION && BLOCK 1536 help 1537 Provide fault-injection capability on end IO handling. This 1538 will make the block layer "forget" an interrupt as configured, 1539 thus exercising the error handling. 1540 1541 Only works with drivers that use the generic timeout handling, 1542 for others it wont do anything. 1543 1544config FAIL_MMC_REQUEST 1545 bool "Fault-injection capability for MMC IO" 1546 depends on FAULT_INJECTION_DEBUG_FS && MMC 1547 help 1548 Provide fault-injection capability for MMC IO. 1549 This will make the mmc core return data errors. This is 1550 useful to test the error handling in the mmc block device 1551 and to test how the mmc host driver handles retries from 1552 the block device. 1553 1554config FAIL_FUTEX 1555 bool "Fault-injection capability for futexes" 1556 select DEBUG_FS 1557 depends on FAULT_INJECTION && FUTEX 1558 help 1559 Provide fault-injection capability for futexes. 1560 1561config FAULT_INJECTION_DEBUG_FS 1562 bool "Debugfs entries for fault-injection capabilities" 1563 depends on FAULT_INJECTION && SYSFS && DEBUG_FS 1564 help 1565 Enable configuration of fault-injection capabilities via debugfs. 1566 1567config FAULT_INJECTION_STACKTRACE_FILTER 1568 bool "stacktrace filter for fault-injection capabilities" 1569 depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT 1570 depends on !X86_64 1571 select STACKTRACE 1572 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE && !X86 1573 help 1574 Provide stacktrace filter for fault-injection capabilities 1575 1576config LATENCYTOP 1577 bool "Latency measuring infrastructure" 1578 depends on DEBUG_KERNEL 1579 depends on STACKTRACE_SUPPORT 1580 depends on PROC_FS 1581 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86 1582 select KALLSYMS 1583 select KALLSYMS_ALL 1584 select STACKTRACE 1585 select SCHEDSTATS 1586 select SCHED_DEBUG 1587 help 1588 Enable this option if you want to use the LatencyTOP tool 1589 to find out which userspace is blocking on what kernel operations. 1590 1591source kernel/trace/Kconfig 1592 1593config PROVIDE_OHCI1394_DMA_INIT 1594 bool "Remote debugging over FireWire early on boot" 1595 depends on PCI && X86 1596 help 1597 If you want to debug problems which hang or crash the kernel early 1598 on boot and the crashing machine has a FireWire port, you can use 1599 this feature to remotely access the memory of the crashed machine 1600 over FireWire. This employs remote DMA as part of the OHCI1394 1601 specification which is now the standard for FireWire controllers. 1602 1603 With remote DMA, you can monitor the printk buffer remotely using 1604 firescope and access all memory below 4GB using fireproxy from gdb. 1605 Even controlling a kernel debugger is possible using remote DMA. 1606 1607 Usage: 1608 1609 If ohci1394_dma=early is used as boot parameter, it will initialize 1610 all OHCI1394 controllers which are found in the PCI config space. 1611 1612 As all changes to the FireWire bus such as enabling and disabling 1613 devices cause a bus reset and thereby disable remote DMA for all 1614 devices, be sure to have the cable plugged and FireWire enabled on 1615 the debugging host before booting the debug target for debugging. 1616 1617 This code (~1k) is freed after boot. By then, the firewire stack 1618 in charge of the OHCI-1394 controllers should be used instead. 1619 1620 See Documentation/debugging-via-ohci1394.txt for more information. 1621 1622config DMA_API_DEBUG 1623 bool "Enable debugging of DMA-API usage" 1624 depends on HAVE_DMA_API_DEBUG 1625 help 1626 Enable this option to debug the use of the DMA API by device drivers. 1627 With this option you will be able to detect common bugs in device 1628 drivers like double-freeing of DMA mappings or freeing mappings that 1629 were never allocated. 1630 1631 This also attempts to catch cases where a page owned by DMA is 1632 accessed by the cpu in a way that could cause data corruption. For 1633 example, this enables cow_user_page() to check that the source page is 1634 not undergoing DMA. 1635 1636 This option causes a performance degradation. Use only if you want to 1637 debug device drivers and dma interactions. 1638 1639 If unsure, say N. 1640 1641menu "Runtime Testing" 1642 1643config LKDTM 1644 tristate "Linux Kernel Dump Test Tool Module" 1645 depends on DEBUG_FS 1646 depends on BLOCK 1647 default n 1648 help 1649 This module enables testing of the different dumping mechanisms by 1650 inducing system failures at predefined crash points. 1651 If you don't need it: say N 1652 Choose M here to compile this code as a module. The module will be 1653 called lkdtm. 1654 1655 Documentation on how to use the module can be found in 1656 Documentation/fault-injection/provoke-crashes.txt 1657 1658config TEST_LIST_SORT 1659 tristate "Linked list sorting test" 1660 depends on DEBUG_KERNEL || m 1661 help 1662 Enable this to turn on 'list_sort()' function test. This test is 1663 executed only once during system boot (so affects only boot time), 1664 or at module load time. 1665 1666 If unsure, say N. 1667 1668config TEST_SORT 1669 tristate "Array-based sort test" 1670 depends on DEBUG_KERNEL || m 1671 help 1672 This option enables the self-test function of 'sort()' at boot, 1673 or at module load time. 1674 1675 If unsure, say N. 1676 1677config KPROBES_SANITY_TEST 1678 bool "Kprobes sanity tests" 1679 depends on DEBUG_KERNEL 1680 depends on KPROBES 1681 default n 1682 help 1683 This option provides for testing basic kprobes functionality on 1684 boot. A sample kprobe, jprobe and kretprobe are inserted and 1685 verified for functionality. 1686 1687 Say N if you are unsure. 1688 1689config BACKTRACE_SELF_TEST 1690 tristate "Self test for the backtrace code" 1691 depends on DEBUG_KERNEL 1692 default n 1693 help 1694 This option provides a kernel module that can be used to test 1695 the kernel stack backtrace code. This option is not useful 1696 for distributions or general kernels, but only for kernel 1697 developers working on architecture code. 1698 1699 Note that if you want to also test saved backtraces, you will 1700 have to enable STACKTRACE as well. 1701 1702 Say N if you are unsure. 1703 1704config RBTREE_TEST 1705 tristate "Red-Black tree test" 1706 depends on DEBUG_KERNEL 1707 help 1708 A benchmark measuring the performance of the rbtree library. 1709 Also includes rbtree invariant checks. 1710 1711config INTERVAL_TREE_TEST 1712 tristate "Interval tree test" 1713 depends on DEBUG_KERNEL 1714 select INTERVAL_TREE 1715 help 1716 A benchmark measuring the performance of the interval tree library 1717 1718config PERCPU_TEST 1719 tristate "Per cpu operations test" 1720 depends on m && DEBUG_KERNEL 1721 help 1722 Enable this option to build test module which validates per-cpu 1723 operations. 1724 1725 If unsure, say N. 1726 1727config ATOMIC64_SELFTEST 1728 tristate "Perform an atomic64_t self-test" 1729 help 1730 Enable this option to test the atomic64_t functions at boot or 1731 at module load time. 1732 1733 If unsure, say N. 1734 1735config ASYNC_RAID6_TEST 1736 tristate "Self test for hardware accelerated raid6 recovery" 1737 depends on ASYNC_RAID6_RECOV 1738 select ASYNC_MEMCPY 1739 ---help--- 1740 This is a one-shot self test that permutes through the 1741 recovery of all the possible two disk failure scenarios for a 1742 N-disk array. Recovery is performed with the asynchronous 1743 raid6 recovery routines, and will optionally use an offload 1744 engine if one is available. 1745 1746 If unsure, say N. 1747 1748config TEST_HEXDUMP 1749 tristate "Test functions located in the hexdump module at runtime" 1750 1751config TEST_STRING_HELPERS 1752 tristate "Test functions located in the string_helpers module at runtime" 1753 1754config TEST_KSTRTOX 1755 tristate "Test kstrto*() family of functions at runtime" 1756 1757config TEST_PRINTF 1758 tristate "Test printf() family of functions at runtime" 1759 1760config TEST_BITMAP 1761 tristate "Test bitmap_*() family of functions at runtime" 1762 default n 1763 help 1764 Enable this option to test the bitmap functions at boot. 1765 1766 If unsure, say N. 1767 1768config TEST_UUID 1769 tristate "Test functions located in the uuid module at runtime" 1770 1771config TEST_RHASHTABLE 1772 tristate "Perform selftest on resizable hash table" 1773 default n 1774 help 1775 Enable this option to test the rhashtable functions at boot. 1776 1777 If unsure, say N. 1778 1779config TEST_HASH 1780 tristate "Perform selftest on hash functions" 1781 default n 1782 help 1783 Enable this option to test the kernel's integer (<linux/hash.h>), 1784 string (<linux/stringhash.h>), and siphash (<linux/siphash.h>) 1785 hash functions on boot (or module load). 1786 1787 This is intended to help people writing architecture-specific 1788 optimized versions. If unsure, say N. 1789 1790config TEST_PARMAN 1791 tristate "Perform selftest on priority array manager" 1792 default n 1793 depends on PARMAN 1794 help 1795 Enable this option to test priority array manager on boot 1796 (or module load). 1797 1798 If unsure, say N. 1799 1800config TEST_LKM 1801 tristate "Test module loading with 'hello world' module" 1802 default n 1803 depends on m 1804 help 1805 This builds the "test_module" module that emits "Hello, world" 1806 on printk when loaded. It is designed to be used for basic 1807 evaluation of the module loading subsystem (for example when 1808 validating module verification). It lacks any extra dependencies, 1809 and will not normally be loaded by the system unless explicitly 1810 requested by name. 1811 1812 If unsure, say N. 1813 1814config TEST_USER_COPY 1815 tristate "Test user/kernel boundary protections" 1816 default n 1817 depends on m 1818 help 1819 This builds the "test_user_copy" module that runs sanity checks 1820 on the copy_to/from_user infrastructure, making sure basic 1821 user/kernel boundary testing is working. If it fails to load, 1822 a regression has been detected in the user/kernel memory boundary 1823 protections. 1824 1825 If unsure, say N. 1826 1827config TEST_BPF 1828 tristate "Test BPF filter functionality" 1829 default n 1830 depends on m && NET 1831 help 1832 This builds the "test_bpf" module that runs various test vectors 1833 against the BPF interpreter or BPF JIT compiler depending on the 1834 current setting. This is in particular useful for BPF JIT compiler 1835 development, but also to run regression tests against changes in 1836 the interpreter code. It also enables test stubs for eBPF maps and 1837 verifier used by user space verifier testsuite. 1838 1839 If unsure, say N. 1840 1841config TEST_FIRMWARE 1842 tristate "Test firmware loading via userspace interface" 1843 default n 1844 depends on FW_LOADER 1845 help 1846 This builds the "test_firmware" module that creates a userspace 1847 interface for testing firmware loading. This can be used to 1848 control the triggering of firmware loading without needing an 1849 actual firmware-using device. The contents can be rechecked by 1850 userspace. 1851 1852 If unsure, say N. 1853 1854config TEST_SYSCTL 1855 tristate "sysctl test driver" 1856 default n 1857 depends on PROC_SYSCTL 1858 help 1859 This builds the "test_sysctl" module. This driver enables to test the 1860 proc sysctl interfaces available to drivers safely without affecting 1861 production knobs which might alter system functionality. 1862 1863 If unsure, say N. 1864 1865config TEST_UDELAY 1866 tristate "udelay test driver" 1867 default n 1868 help 1869 This builds the "udelay_test" module that helps to make sure 1870 that udelay() is working properly. 1871 1872 If unsure, say N. 1873 1874config TEST_STATIC_KEYS 1875 tristate "Test static keys" 1876 default n 1877 depends on m 1878 help 1879 Test the static key interfaces. 1880 1881 If unsure, say N. 1882 1883config TEST_KMOD 1884 tristate "kmod stress tester" 1885 default n 1886 depends on m 1887 depends on BLOCK && (64BIT || LBDAF) # for XFS, BTRFS 1888 depends on NETDEVICES && NET_CORE && INET # for TUN 1889 select TEST_LKM 1890 select XFS_FS 1891 select TUN 1892 select BTRFS_FS 1893 help 1894 Test the kernel's module loading mechanism: kmod. kmod implements 1895 support to load modules using the Linux kernel's usermode helper. 1896 This test provides a series of tests against kmod. 1897 1898 Although technically you can either build test_kmod as a module or 1899 into the kernel we disallow building it into the kernel since 1900 it stress tests request_module() and this will very likely cause 1901 some issues by taking over precious threads available from other 1902 module load requests, ultimately this could be fatal. 1903 1904 To run tests run: 1905 1906 tools/testing/selftests/kmod/kmod.sh --help 1907 1908 If unsure, say N. 1909 1910config TEST_DEBUG_VIRTUAL 1911 tristate "Test CONFIG_DEBUG_VIRTUAL feature" 1912 depends on DEBUG_VIRTUAL 1913 help 1914 Test the kernel's ability to detect incorrect calls to 1915 virt_to_phys() done against the non-linear part of the 1916 kernel's virtual address map. 1917 1918 If unsure, say N. 1919 1920endmenu # runtime tests 1921 1922config MEMTEST 1923 bool "Memtest" 1924 depends on HAVE_MEMBLOCK 1925 ---help--- 1926 This option adds a kernel parameter 'memtest', which allows memtest 1927 to be set. 1928 memtest=0, mean disabled; -- default 1929 memtest=1, mean do 1 test pattern; 1930 ... 1931 memtest=17, mean do 17 test patterns. 1932 If you are unsure how to answer this question, answer N. 1933 1934config BUG_ON_DATA_CORRUPTION 1935 bool "Trigger a BUG when data corruption is detected" 1936 select DEBUG_LIST 1937 help 1938 Select this option if the kernel should BUG when it encounters 1939 data corruption in kernel memory structures when they get checked 1940 for validity. 1941 1942 If unsure, say N. 1943 1944source "samples/Kconfig" 1945 1946source "lib/Kconfig.kgdb" 1947 1948source "lib/Kconfig.ubsan" 1949 1950config ARCH_HAS_DEVMEM_IS_ALLOWED 1951 bool 1952 1953config STRICT_DEVMEM 1954 bool "Filter access to /dev/mem" 1955 depends on MMU && DEVMEM 1956 depends on ARCH_HAS_DEVMEM_IS_ALLOWED 1957 default y if TILE || PPC 1958 ---help--- 1959 If this option is disabled, you allow userspace (root) access to all 1960 of memory, including kernel and userspace memory. Accidental 1961 access to this is obviously disastrous, but specific access can 1962 be used by people debugging the kernel. Note that with PAT support 1963 enabled, even in this case there are restrictions on /dev/mem 1964 use due to the cache aliasing requirements. 1965 1966 If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem 1967 file only allows userspace access to PCI space and the BIOS code and 1968 data regions. This is sufficient for dosemu and X and all common 1969 users of /dev/mem. 1970 1971 If in doubt, say Y. 1972 1973config IO_STRICT_DEVMEM 1974 bool "Filter I/O access to /dev/mem" 1975 depends on STRICT_DEVMEM 1976 ---help--- 1977 If this option is disabled, you allow userspace (root) access to all 1978 io-memory regardless of whether a driver is actively using that 1979 range. Accidental access to this is obviously disastrous, but 1980 specific access can be used by people debugging kernel drivers. 1981 1982 If this option is switched on, the /dev/mem file only allows 1983 userspace access to *idle* io-memory ranges (see /proc/iomem) This 1984 may break traditional users of /dev/mem (dosemu, legacy X, etc...) 1985 if the driver using a given range cannot be disabled. 1986 1987 If in doubt, say Y. 1988