Revision tags: v6.12-rc4 |
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be602cde |
| 17-Oct-2024 |
Ingo Molnar <mingo@kernel.org> |
Merge branch 'linus' into sched/urgent, to resolve conflict
Conflicts: kernel/sched/ext.c
There's a context conflict between this upstream commit:
3fdb9ebcec10 sched_ext: Start schedulers with
Merge branch 'linus' into sched/urgent, to resolve conflict
Conflicts: kernel/sched/ext.c
There's a context conflict between this upstream commit:
3fdb9ebcec10 sched_ext: Start schedulers with consistent p->scx.slice values
... and this fix in sched/urgent:
98442f0ccd82 sched: Fix delayed_dequeue vs switched_from_fair()
Resolve it.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Revision tags: v6.12-rc3 |
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a1029768 |
| 11-Oct-2024 |
Linus Torvalds <torvalds@linux-foundation.org> |
Merge tag 'rcu.fixes.6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU fix from Neeraj Upadhyay: "Fix rcuog kthread wakeup invocation from softirq context on a CPU whi
Merge tag 'rcu.fixes.6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU fix from Neeraj Upadhyay: "Fix rcuog kthread wakeup invocation from softirq context on a CPU which has been marked offline.
This can happen when new callbacks are enqueued from a softirq on an offline CPU before it calls rcutree_report_cpu_dead(). When this happens on NOCB configuration, the rcuog wake-up is deferred through an IPI to an online CPU. This is done to avoid call into the scheduler which can risk arming the RT-bandwidth after hrtimers have been migrated out and disabled.
However, doing IPI call from softirq is not allowed: Fix this by forcing deferred rcuog wakeup through the NOCB timer when the CPU is offline"
* tag 'rcu.fixes.6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: rcu/nocb: Fix rcuog wake-up from offline softirq
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f7345ccc |
| 10-Oct-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Fix rcuog wake-up from offline softirq
After a CPU has set itself offline and before it eventually calls rcutree_report_cpu_dead(), there are still opportunities for callbacks to be enqueu
rcu/nocb: Fix rcuog wake-up from offline softirq
After a CPU has set itself offline and before it eventually calls rcutree_report_cpu_dead(), there are still opportunities for callbacks to be enqueued, for example from a softirq. When that happens on NOCB, the rcuog wake-up is deferred through an IPI to an online CPU in order not to call into the scheduler and risk arming the RT-bandwidth after hrtimers have been migrated out and disabled.
But performing a synchronized IPI from a softirq is buggy as reported in the following scenario:
WARNING: CPU: 1 PID: 26 at kernel/smp.c:633 smp_call_function_single Modules linked in: rcutorture torture CPU: 1 UID: 0 PID: 26 Comm: migration/1 Not tainted 6.11.0-rc1-00012-g9139f93209d1 #1 Stopper: multi_cpu_stop+0x0/0x320 <- __stop_cpus+0xd0/0x120 RIP: 0010:smp_call_function_single <IRQ> swake_up_one_online __call_rcu_nocb_wake __call_rcu_common ? rcu_torture_one_read call_timer_fn __run_timers run_timer_softirq handle_softirqs irq_exit_rcu ? tick_handle_periodic sysvec_apic_timer_interrupt </IRQ>
Fix this with forcing deferred rcuog wake up through the NOCB timer when the CPU is offline. The actual wake up will happen from rcutree_report_cpu_dead().
Reported-by: kernel test robot <oliver.sang@intel.com> Closes: https://lore.kernel.org/oe-lkp/202409231644.4c55582d-lkp@intel.com Fixes: 9139f93209d1 ("rcu/nocb: Fix RT throttling hrtimer armed from offline CPU") Reviewed-by: "Joel Fernandes (Google)" <joel@joelfernandes.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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Revision tags: v6.12-rc2 |
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c8d430db |
| 06-Oct-2024 |
Paolo Bonzini <pbonzini@redhat.com> |
Merge tag 'kvmarm-fixes-6.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
KVM/arm64 fixes for 6.12, take #1
- Fix pKVM error path on init, making sure we do not chang
Merge tag 'kvmarm-fixes-6.12-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
KVM/arm64 fixes for 6.12, take #1
- Fix pKVM error path on init, making sure we do not change critical system registers as we're about to fail
- Make sure that the host's vector length is at capped by a value common to all CPUs
- Fix kvm_has_feat*() handling of "negative" features, as the current code is pretty broken
- Promote Joey to the status of official reviewer, while James steps down -- hopefully only temporarly
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0c436dfe |
| 02-Oct-2024 |
Takashi Iwai <tiwai@suse.de> |
Merge tag 'asoc-fix-v6.12-rc1' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into for-linus
ASoC: Fixes for v6.12
A bunch of fixes here that came in during the merge window and t
Merge tag 'asoc-fix-v6.12-rc1' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into for-linus
ASoC: Fixes for v6.12
A bunch of fixes here that came in during the merge window and the first week of release, plus some new quirks and device IDs. There's nothing major here, it's a bit bigger than it might've been due to there being no fixes sent during the merge window due to your vacation.
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2cd86f02 |
| 01-Oct-2024 |
Maarten Lankhorst <maarten.lankhorst@linux.intel.com> |
Merge remote-tracking branch 'drm/drm-fixes' into drm-misc-fixes
Required for a panthor fix that broke when FOP_UNSIGNED_OFFSET was added in place of FMODE_UNSIGNED_OFFSET.
Signed-off-by: Maarten L
Merge remote-tracking branch 'drm/drm-fixes' into drm-misc-fixes
Required for a panthor fix that broke when FOP_UNSIGNED_OFFSET was added in place of FMODE_UNSIGNED_OFFSET.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
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Revision tags: v6.12-rc1 |
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3a39d672 |
| 27-Sep-2024 |
Paolo Abeni <pabeni@redhat.com> |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
Cross-merge networking fixes after downstream PR.
No conflicts and no adjacent changes.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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36ec807b |
| 20-Sep-2024 |
Dmitry Torokhov <dmitry.torokhov@gmail.com> |
Merge branch 'next' into for-linus
Prepare input updates for 6.12 merge window.
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Revision tags: v6.11, v6.11-rc7 |
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f057b572 |
| 06-Sep-2024 |
Dmitry Torokhov <dmitry.torokhov@gmail.com> |
Merge branch 'ib/6.11-rc6-matrix-keypad-spitz' into next
Bring in changes removing support for platform data from matrix-keypad driver.
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Revision tags: v6.11-rc6, v6.11-rc5, v6.11-rc4, v6.11-rc3, v6.11-rc2 |
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66e72a01 |
| 29-Jul-2024 |
Jerome Brunet <jbrunet@baylibre.com> |
Merge tag 'v6.11-rc1' into clk-meson-next
Linux 6.11-rc1
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ee057c8c |
| 14-Aug-2024 |
Steven Rostedt <rostedt@goodmis.org> |
Merge tag 'v6.11-rc3' into trace/ring-buffer/core
The "reserve_mem" kernel command line parameter has been pulled into v6.11. Merge the latest -rc3 to allow the persistent ring buffer memory to be a
Merge tag 'v6.11-rc3' into trace/ring-buffer/core
The "reserve_mem" kernel command line parameter has been pulled into v6.11. Merge the latest -rc3 to allow the persistent ring buffer memory to be able to be mapped at the address specified by the "reserve_mem" command line parameter.
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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c8faf11c |
| 30-Jul-2024 |
Tejun Heo <tj@kernel.org> |
Merge tag 'v6.11-rc1' into for-6.12
Linux 6.11-rc1
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ed7171ff |
| 16-Aug-2024 |
Lucas De Marchi <lucas.demarchi@intel.com> |
Merge drm/drm-next into drm-xe-next
Get drm-xe-next on v6.11-rc2 and synchronized with drm-intel-next for the display side. This resolves the current conflict for the enable_display module parameter
Merge drm/drm-next into drm-xe-next
Get drm-xe-next on v6.11-rc2 and synchronized with drm-intel-next for the display side. This resolves the current conflict for the enable_display module parameter and allows further pending refactors.
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
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5c61f598 |
| 12-Aug-2024 |
Thomas Zimmermann <tzimmermann@suse.de> |
Merge drm/drm-next into drm-misc-next
Get drm-misc-next to the state of v6.11-rc2.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
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3663e2c4 |
| 01-Aug-2024 |
Jani Nikula <jani.nikula@intel.com> |
Merge drm/drm-next into drm-intel-next
Sync with v6.11-rc1 in general, and specifically get the new BACKLIGHT_POWER_ constants for power states.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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067610eb |
| 18-Sep-2024 |
Linus Torvalds <torvalds@linux-foundation.org> |
Merge tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Neeraj Upadhyay: "Context tracking: - rename context tracking state related symbols
Merge tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux
Pull RCU updates from Neeraj Upadhyay: "Context tracking: - rename context tracking state related symbols and remove references to "dynticks" in various context tracking state variables and related helpers - force context_tracking_enabled_this_cpu() to be inlined to avoid leaving a noinstr section
CSD lock: - enhance CSD-lock diagnostic reports - add an API to provide an indication of ongoing CSD-lock stall
nocb: - update and simplify RCU nocb code to handle (de-)offloading of callbacks only for offline CPUs - fix RT throttling hrtimer being armed from offline CPU
rcutorture: - remove redundant rcu_torture_ops get_gp_completed fields - add SRCU ->same_gp_state and ->get_comp_state functions - add generic test for NUM_ACTIVE_*RCU_POLL* for testing RCU and SRCU polled grace periods - add CFcommon.arch for arch-specific Kconfig options - print number of update types in rcu_torture_write_types() - add rcutree.nohz_full_patience_delay testing to the TREE07 scenario - add a stall_cpu_repeat module parameter to test repeated CPU stalls - add argument to limit number of CPUs a guest OS can use in torture.sh
rcustall: - abbreviate RCU CPU stall warnings during CSD-lock stalls - Allow dump_cpu_task() to be called without disabling preemption - defer printing stall-warning backtrace when holding rcu_node lock
srcu: - make SRCU gp seq wrap-around faster - add KCSAN checks for concurrent updates to ->srcu_n_exp_nodelay and ->reschedule_count which are used in heuristics governing auto-expediting of normal SRCU grace periods and grace-period-state-machine delays - mark idle SRCU-barrier callbacks to help identify stuck SRCU-barrier callback
rcu tasks: - remove RCU Tasks Rude asynchronous APIs as they are no longer used - stop testing RCU Tasks Rude asynchronous APIs - fix access to non-existent percpu regions - check processor-ID assumptions during chosen CPU calculation for callback enqueuing - update description of rtp->tasks_gp_seq grace-period sequence number - add rcu_barrier_cb_is_done() to identify whether a given rcu_barrier callback is stuck - mark idle Tasks-RCU-barrier callbacks - add *torture_stats_print() functions to print detailed diagnostics for Tasks-RCU variants - capture start time of rcu_barrier_tasks*() operation to help distinguish a hung barrier operation from a long series of barrier operations
refscale: - add a TINY scenario to support tests of Tiny RCU and Tiny SRCU - optimize process_durations() operation
rcuscale: - dump stacks of stalled rcu_scale_writer() instances and grace-period statistics when rcu_scale_writer() stalls - mark idle RCU-barrier callbacks to identify stuck RCU-barrier callbacks - print detailed grace-period and barrier diagnostics on rcu_scale_writer() hangs for Tasks-RCU variants - warn if async module parameter is specified for RCU implementations that do not have async primitives such as RCU Tasks Rude - make all writer tasks report upon hang - tolerate repeated GFP_KERNEL failure in rcu_scale_writer() - use special allocator for rcu_scale_writer() - NULL out top-level pointers to heap memory to avoid double-free bugs on modprobe failures - maintain per-task instead of per-CPU callbacks count to avoid any issues with migration of either tasks or callbacks - constify struct ref_scale_ops
Fixes: - use system_unbound_wq for kfree_rcu work to avoid disturbing isolated CPUs
Misc: - warn on unexpected rcu_state.srs_done_tail state - better define "atomic" for list_replace_rcu() and hlist_replace_rcu() routines - annotate struct kvfree_rcu_bulk_data with __counted_by()"
* tag 'rcu.release.v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (90 commits) rcu: Defer printing stall-warning backtrace when holding rcu_node lock rcu/nocb: Remove superfluous memory barrier after bypass enqueue rcu/nocb: Conditionally wake up rcuo if not already waiting on GP rcu/nocb: Fix RT throttling hrtimer armed from offline CPU rcu/nocb: Simplify (de-)offloading state machine context_tracking: Tag context_tracking_enabled_this_cpu() __always_inline context_tracking, rcu: Rename rcu_dyntick trace event into rcu_watching rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}() rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs() rcu: Rename rcu_implicit_dynticks_qs() into rcu_watching_snap_recheck() rcu: Rename dyntick_save_progress_counter() into rcu_watching_snap_save() rcu: Rename struct rcu_data .exp_dynticks_snap into .exp_watching_snap rcu: Rename struct rcu_data .dynticks_snap into .watching_snap rcu: Rename rcu_dynticks_zero_in_eqs() into rcu_watching_zero_in_eqs() rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since() rcu: Rename rcu_dynticks_in_eqs() into rcu_watching_snap_in_eqs() rcu: Rename rcu_dynticks_eqs_online() into rcu_watching_online() context_tracking, rcu: Rename rcu_dynticks_curr_cpu_in_eqs() into rcu_is_watching_curr_cpu() context_tracking, rcu: Rename rcu_dynticks_task*() into rcu_task*() refscale: Constify struct ref_scale_ops ...
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355debb8 |
| 08-Sep-2024 |
Neeraj Upadhyay <neeraj.upadhyay@kernel.org> |
Merge branches 'context_tracking.15.08.24a', 'csd.lock.15.08.24a', 'nocb.09.09.24a', 'rcutorture.14.08.24a', 'rcustall.09.09.24a', 'srcu.12.08.24a', 'rcu.tasks.14.08.24a', 'rcu_scaling_tests.15.08.24
Merge branches 'context_tracking.15.08.24a', 'csd.lock.15.08.24a', 'nocb.09.09.24a', 'rcutorture.14.08.24a', 'rcustall.09.09.24a', 'srcu.12.08.24a', 'rcu.tasks.14.08.24a', 'rcu_scaling_tests.15.08.24a', 'fixes.12.08.24a' and 'misc.11.08.24a' into next.09.09.24a
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#
7562eed2 |
| 14-Aug-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Remove superfluous memory barrier after bypass enqueue
Pre-GP accesses performed by the update side must be ordered against post-GP accesses performed by the readers. This is ensured by th
rcu/nocb: Remove superfluous memory barrier after bypass enqueue
Pre-GP accesses performed by the update side must be ordered against post-GP accesses performed by the readers. This is ensured by the bypass or nocb locking on enqueue time, followed by the fully ordered rnp locking initiated while callbacks are accelerated, and then propagated throughout the whole GP lifecyle associated with the callbacks.
Therefore the explicit barrier advertizing ordering between bypass enqueue and rcuo wakeup is superfluous. If anything, it would even only order the first bypass callback enqueue against the rcuo wakeup and ignore all the subsequent ones.
Remove the needless barrier.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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1b022b87 |
| 14-Aug-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Conditionally wake up rcuo if not already waiting on GP
A callback enqueuer currently wakes up the rcuo kthread if it is adding the first non-done callback of a CPU, whether the kthread is
rcu/nocb: Conditionally wake up rcuo if not already waiting on GP
A callback enqueuer currently wakes up the rcuo kthread if it is adding the first non-done callback of a CPU, whether the kthread is waiting on a grace period or not (unless the CPU is offline).
This looks like a desired behaviour because then the rcuo kthread doesn't wait for the end of the current grace period to handle the callback. It is accelerated right away and assigned to the next grace period. The GP kthread is notified about that fact and iterates with the upcoming GP without sleeping in-between.
However this best-case scenario is contradicted by a few details, depending on the situation:
1) If the callback is a non-bypass one queued with IRQs enabled, the wake up only occurs if no other pending callbacks are on the list. Therefore the theoretical "optimization" actually applies on rare occasions.
2) If the callback is a non-bypass one queued with IRQs disabled, the situation is similar with even more uncertainty due to the deferred wake up.
3) If the callback is lazy, a few jiffies don't make any difference.
4) If the callback is bypass, the wake up timer is programmed 2 jiffies ahead by rcuo in case the regular pending queue has been handled in the meantime. The rare storm of callbacks can otherwise wait for the currently elapsing grace period to be flushed and handled.
For all those reasons, the optimization is only theoretical and occasional. Therefore it is reasonable that callbacks enqueuers only wake up the rcuo kthread when it is not already waiting on a grace period to complete.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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9139f932 |
| 14-Aug-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Fix RT throttling hrtimer armed from offline CPU
After a CPU is marked offline and until it reaches its final trip to idle, rcuo has several opportunities to be woken up, either because a
rcu/nocb: Fix RT throttling hrtimer armed from offline CPU
After a CPU is marked offline and until it reaches its final trip to idle, rcuo has several opportunities to be woken up, either because a callback has been queued in the meantime or because rcutree_report_cpu_dead() has issued the final deferred NOCB wake up.
If RCU-boosting is enabled, RCU kthreads are set to SCHED_FIFO policy. And if RT-bandwidth is enabled, the related hrtimer might be armed. However this then happens after hrtimers have been migrated at the CPUHP_AP_HRTIMERS_DYING stage, which is broken as reported by the following warning:
Call trace: enqueue_hrtimer+0x7c/0xf8 hrtimer_start_range_ns+0x2b8/0x300 enqueue_task_rt+0x298/0x3f0 enqueue_task+0x94/0x188 ttwu_do_activate+0xb4/0x27c try_to_wake_up+0x2d8/0x79c wake_up_process+0x18/0x28 __wake_nocb_gp+0x80/0x1a0 do_nocb_deferred_wakeup_common+0x3c/0xcc rcu_report_dead+0x68/0x1ac cpuhp_report_idle_dead+0x48/0x9c do_idle+0x288/0x294 cpu_startup_entry+0x34/0x3c secondary_start_kernel+0x138/0x158
Fix this with waking up rcuo using an IPI if necessary. Since the existing API to deal with this situation only handles swait queue, rcuo is only woken up from offline CPUs if it's not already waiting on a grace period. In the worst case some callbacks will just wait for a grace period to complete before being assigned to a subsequent one.
Reported-by: "Cheng-Jui Wang (王正睿)" <Cheng-Jui.Wang@mediatek.com> Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier") Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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Revision tags: v6.11-rc1, v6.10, v6.10-rc7 |
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1fcb932c |
| 04-Jul-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Simplify (de-)offloading state machine
Now that the (de-)offloading process can only apply to offline CPUs, there is no more concurrency between rcu_core and nocb kthreads. Also the mutati
rcu/nocb: Simplify (de-)offloading state machine
Now that the (de-)offloading process can only apply to offline CPUs, there is no more concurrency between rcu_core and nocb kthreads. Also the mutation now happens on empty queues.
Therefore the state machine can be reduced to a single bit called SEGCBLIST_OFFLOADED. Simplify the transition as follows:
* Upon offloading: queue the rdp to be added to the rcuog list and wait for the rcuog kthread to set the SEGCBLIST_OFFLOADED bit. Unpark rcuo kthread.
* Upon de-offloading: Park rcuo kthread. Queue the rdp to be removed from the rcuog list and wait for the rcuog kthread to clear the SEGCBLIST_OFFLOADED bit.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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Revision tags: v6.10-rc6, v6.10-rc5, v6.10-rc4, v6.10-rc3, v6.10-rc2, v6.10-rc1, v6.9, v6.9-rc7 |
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32a9f26e |
| 29-Apr-2024 |
Valentin Schneider <vschneid@redhat.com> |
rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs()
The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, replace "dyntick_idle" into "eqs" to drop the
rcu: Rename rcu_momentary_dyntick_idle() into rcu_momentary_eqs()
The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, replace "dyntick_idle" into "eqs" to drop the dyntick reference.
Signed-off-by: Valentin Schneider <vschneid@redhat.com> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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bae6076e |
| 30-May-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Remove SEGCBLIST_RCU_CORE
RCU core can't be running anymore while in the middle of (de-)offloading since this sort of transition now only applies to offline CPUs.
The SEGCBLIST_RCU_CORE s
rcu/nocb: Remove SEGCBLIST_RCU_CORE
RCU core can't be running anymore while in the middle of (de-)offloading since this sort of transition now only applies to offline CPUs.
The SEGCBLIST_RCU_CORE state can therefore be removed.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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d2e7f55f |
| 30-May-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: Remove halfway (de-)offloading handling from bypass
Bypass enqueue can't happen anymore in the middle of (de-)offloading since this sort of transition now only applies to offline CPUs.
Th
rcu/nocb: Remove halfway (de-)offloading handling from bypass
Bypass enqueue can't happen anymore in the middle of (de-)offloading since this sort of transition now only applies to offline CPUs.
The related safety check can therefore be removed.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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4e26ce42 |
| 30-May-2024 |
Frederic Weisbecker <frederic@kernel.org> |
rcu/nocb: (De-)offload callbacks on offline CPUs only
Currently callbacks can be (de-)offloaded only on online CPUs. This involves an overly elaborated state machine in order to make sure that callb
rcu/nocb: (De-)offload callbacks on offline CPUs only
Currently callbacks can be (de-)offloaded only on online CPUs. This involves an overly elaborated state machine in order to make sure that callbacks are always handled during the process while ensuring synchronization between rcu_core and NOCB kthreads.
The only potential user of NOCB (de-)offloading appears to be a nohz_full toggling interface through cpusets. And the general agreement is now to work toward toggling the nohz_full state on offline CPUs to simplify the whole picture.
Therefore, convert the (de-)offloading to only support offline CPUs. This involves the following changes:
* Call rcu_barrier() before deoffloading. An offline offloaded CPU may still carry callbacks in its queue ignored by rcutree_migrate_callbacks(). Those callbacks must all be flushed before switching to a regular queue because no more kthreads will handle those before the CPU ever gets re-onlined.
This means that further calls to rcu_barrier() will find an empty queue until the CPU goes through rcutree_report_cpu_starting(). As a result it is guaranteed that further rcu_barrier() won't try to lock the nocb_lock for that target and thus won't risk an imbalance.
Therefore barrier_mutex doesn't need to be locked anymore upon deoffloading.
* Assume the queue is empty before offloading, as rcutree_migrate_callbacks() took care of everything.
This means that further calls to rcu_barrier() will find an empty queue until the CPU goes through rcutree_report_cpu_starting(). As a result it is guaranteed that further rcu_barrier() won't risk a nocb_lock imbalance.
Therefore barrier_mutex doesn't need to be locked anymore upon offloading.
* No need to flush bypass anymore.
Further simplifications will follow in upcoming patches.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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