en Copyright 2015 Java http://kernelsources.org:8080/source/history/linux/arch/loongarch/include/asm/current.h#51cb1aa1250c36269474b8b6ca6b6319e170f5a5 Merge tag 'loongarch-7.2' of git://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongsonPull LoongArch updates from Huacai Chen: - Add THREAD_INFO_IN_TASK implementation - Add build salt to the vDSO - Add some BPF JIT inline helpers - Update DTS for I2C clocks and clock-frequency - Some bug fixes and other small changes* tag 'loongarch-7.2' of git://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson: selftests/bpf: Test jited inline of bpf_get_smp_processor_id() for LoongArch selftests/bpf: Test jited inline of bpf_get_current_task() for LoongArch selftests/bpf: Add __arch_loongarch to limit test cases for LoongArch selftests/bpf: Add get_preempt_count() support for LoongArch LoongArch: dts: Add i2c clocks and clock-frequency properties to LS2K2000 LoongArch: dts: Add i2c clocks and clock-frequency properties to LS2K1000 LoongArch: dts: Add i2c clocks and clock-frequency properties to LS2K0500 LoongArch: BPF: Inline bpf_get_smp_processor_id() helper LoongArch: BPF: Inline bpf_get_current_task/_btf() helpers LoongArch: BPF: Fix off-by-one error in tail call LoongArch: BPF: Fix outdated tail call comments LoongArch: Add build salt to the vDSO LoongArch: Fix nr passing in set_direct_map_valid_noflush() LoongArch: Fix missing dirty page tracking in {pte,pmd}_wrprotect() LoongArch: Move struct kimage forward declaration before use LoongArch: Report dying CPU to RCU in stop_this_cpu() LoongArch: Add PIO for early access before ACPI PCI root register LoongArch: Add THREAD_INFO_IN_TASK implementation List of files: /linux/arch/loongarch/include/asm/current.h Fri, 26 Jun 2026 17:42:49 +0200 Linus Torvalds <torvalds@linux-foundation.org> http://kernelsources.org:8080/source/history/linux/arch/loongarch/include/asm/current.h#7b5944d6ed369e43aeaf37beba9f89f7fb6c633b LoongArch: Add THREAD_INFO_IN_TASK implementationLike other architectures such as x86, arm64, riscv, powerpc and s390,select THREAD_INFO_IN_TASK for LoongArch to move thread_info off thestack into task_struct. This follows modern kernel standards and alsomakes the system more secure.With this patch, thread_info is included in task_struct at an offsetof 0 instead of being placed at the bottom of the kernel stack. Thus,the $tp register points to both thread_info and task_struct.To support this, introduce a per-CPU variable cpu_tasks to store thepointer to the current task_struct. This decouples the recovery of the$tp register from the stack pointer during exception entry.Then initialize cpu_tasks for the primary and secondary CPUs duringarch-specific setup and SMP boot paths. To eliminate the dangerouswindows during the early initialization where the cpu_tasks remainsuninitialized, set_current() is invoked as early as possible in bothsetup_arch() and start_secondary(). This ensures the $tp recoverybarrier is armed in case any early boot exceptions or kernel panicsoccur.Modify SAVE_SOME and handle_syscall to restore the $tp register fromcpu_tasks, and also use the la_abs absolute addressing for cpu_tasksaccess in assembly to bypass the relocation limits within exceptionhandling sections. By advancing the preservation of u0 in SAVE_SOME,we reuse the PERCPU_BASE_KS value in u0 for the cpu_tasks calculation,effectively eliminating a duplicate csrrd instruction execution on SMPplatforms.Update <asm/switch_to.h> and <kernel/switch.S> to fully support theCONFIG_THREAD_INFO_IN_TASK feature.Remove the obsolete next_ti argument from __switch_to(), which shiftsthe remaining arguments ahead in the calling convention (sched_ra froma3 to a2, and sched_cfa from a4 to a3). Under the new configuration,__switch_to() now directly derives the thread pointer ($tp) from thenext task_struct pointer in a1.To preserve the optimal and clean "move tp, a1" path for 64-bit kernels,the thread pointer ($tp) is assigned directly from a1 in the core path.For 32-bit kernels, where a1 carries a 2000-byte structural pointer biasat entry, an explicit adjustment "PTR_ADDI tp, tp, -TASK_STRUCT_OFFSET"is introduced at the function exit.In the context of __switch_to(), local interrupts are disabled, and thekernel is in a critical switching phase where handling any synchronousexception is practically impossible and prohibited.If any synchronous exception or watchpoint does trigger in this narrowwindow, it constitutes a fatal double fault and the kernel is expectedto die/panic immediately anyway. Therefore, the temporary biased valuein $tp is safe and acceptable here.Additionally, evaluate the stack lookup as a single load instruction"LONG_LPTR t0, a1, (TASK_STACK - TASK_STRUCT_OFFSET)", this perfectlysatisfies both 32-bit and 64-bit kernels. Using the "next" pointer ina1 as the base register, rather than $tp, effectively unchains the datadependency (RAW hazard) from the preceding move instruction, maximizingthe instruction-level parallelism and superscalar execution efficiencywhile naturally adapting the structural shift.With CONFIG_THREAD_INFO_IN_TASK enabled, the kernel stack life cycle isdecoupled from task_struct and can be freed concurrently.Currently, show_stacktrace() reads raw stack data via __get_addr() andsubsequently calls show_backtrace() to unwind the frame, without holdingany reference to the target task's stack. If show_stacktrace() is calledon a concurrently exiting task, it could attempt to read from a freed orreallocated kernel stack. This introduces a severe use-after-free (UAF)read risk or kernel panics.Wrap the entire stack inspection process inside show_stacktrace() witha try_get_task_stack() and put_task_stack() pair. This ensures the taskstack remains pinned safely during both the raw stack data dump loop andthe subsequent stack unwinding phase.Also, ensure that the task pointer is initialized to "current" early ifit is NULL, so that try_get_task_stack() always operates on a valid taskreference.Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> List of files: /linux/arch/loongarch/include/asm/current.h Thu, 25 Jun 2026 07:03:47 +0200 Tiezhu Yang <yangtiezhu@loongson.cn>