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Message-ID: <1ec831dd-1070-d1f0-1502-5b8e493caab0@redhat.com>
Date: Wed, 26 Apr 2023 13:44:33 -0400
From: Waiman Long <longman@...hat.com>
To: Wander Lairson Costa <wander@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Will Deacon <will@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Huacai Chen <chenhuacai@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Oleg Nesterov <oleg@...hat.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Christian Brauner <brauner@...nel.org>,
Kees Cook <keescook@...omium.org>,
Andrei Vagin <avagin@...il.com>,
Shakeel Butt <shakeelb@...gle.com>,
open list <linux-kernel@...r.kernel.org>,
"open list:PERFORMANCE EVENTS SUBSYSTEM"
<linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH v7 0/3] Introduce put_task_struct_atomic_sleep()
On 4/25/23 07:43, Wander Lairson Costa wrote:
> 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(-)
This patch series looks good to me.
Acked-by: Waiman Long <longman@...hat.com>
I notice that __put_task_struct() invokes quite a bit of cleanup works
from different subsystems. So it may burn quite a bit of cpu cycles to
complete. This may not be something we want in an atomic context, maybe
we should call call_rcu() irrespective of the PREEMPT_RT setting.
Anyway, this can be a follow-up patch if we want to do that.
Cheers,
Longman
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