Messages in this thread | | | From | Wander Lairson Costa <> | Subject | [PATCH v7 0/3] Introduce put_task_struct_atomic_sleep() | Date | Tue, 25 Apr 2023 08:43:00 -0300 |
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The put_task_struct() function reduces a usage counter and invokes __put_task_struct() when the counter reaches zero.
In the case of __put_task_struct(), it indirectly acquires a spinlock, which operates as a sleeping lock under the PREEMPT_RT configuration. As a result, invoking put_task_struct() within an atomic context is not feasible for real-time (RT) kernels.
One practical example is a splat inside inactive_task_timer(), which is called in a interrupt context:
CPU: 1 PID: 2848 Comm: life Kdump: loaded Tainted: G W --------- Hardware name: HP ProLiant DL388p Gen8, BIOS P70 07/15/2012 Call Trace: dump_stack_lvl+0x57/0x7d mark_lock_irq.cold+0x33/0xba ? stack_trace_save+0x4b/0x70 ? save_trace+0x55/0x150 mark_lock+0x1e7/0x400 mark_usage+0x11d/0x140 __lock_acquire+0x30d/0x930 lock_acquire.part.0+0x9c/0x210 ? refill_obj_stock+0x3d/0x3a0 ? rcu_read_lock_sched_held+0x3f/0x70 ? trace_lock_acquire+0x38/0x140 ? lock_acquire+0x30/0x80 ? refill_obj_stock+0x3d/0x3a0 rt_spin_lock+0x27/0xe0 ? refill_obj_stock+0x3d/0x3a0 refill_obj_stock+0x3d/0x3a0 ? inactive_task_timer+0x1ad/0x340 kmem_cache_free+0x357/0x560 inactive_task_timer+0x1ad/0x340 ? switched_from_dl+0x2d0/0x2d0 __run_hrtimer+0x8a/0x1a0 __hrtimer_run_queues+0x91/0x130 hrtimer_interrupt+0x10f/0x220 __sysvec_apic_timer_interrupt+0x7b/0xd0 sysvec_apic_timer_interrupt+0x4f/0xd0 ? asm_sysvec_apic_timer_interrupt+0xa/0x20 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7fff196bf6f5
To address this issue, this patch series introduces a new function called put_task_struct_atomic_safe(). When compiled with the PREEMPT_RT configuration, this function defers the call to __put_task_struct() to a process context.
Additionally, the patch series rectifies known problematic call sites to ensure smooth functioning.
Changelog =========
v1: * Initial implementation fixing the splat.
v2: * Isolate the logic in its own function. * Fix two more cases caught in review.
v3: * Change __put_task_struct() to handle the issue internally.
v4: * Explain why call_rcu() is safe to call from interrupt context.
v5: * Explain why __put_task_struct() doesn't conflict with put_task_sruct_rcu_user.
v6: * As per Sebastian's review, revert back the implementation of v2 with a distinct function. * Add a check in put_task_struct() to warning when called from a non-sleepable context. * Address more call sites.
v7: * Fix typos. * Add an explanation why the new function doesn't conflict with delayed_free_task().
Wander Lairson Costa (3): sched/core: warn on call put_task_struct in invalid context sched/task: Add the put_task_struct_atomic_safe() function treewide: replace put_task_struct() with the atomic safe version
include/linux/sched/task.h | 49 ++++++++++++++++++++++++++++++++++++++ kernel/events/core.c | 6 ++--- kernel/fork.c | 8 +++++++ kernel/locking/rtmutex.c | 10 ++++---- kernel/sched/core.c | 6 ++--- kernel/sched/deadline.c | 16 ++++++------- kernel/sched/rt.c | 4 ++-- 7 files changed, 78 insertions(+), 21 deletions(-)
-- 2.40.0
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