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From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Peter Zijlstra <peterz@infradead.org>,
	gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, joe.lawrence@redhat.com,
	fweisbec@gmail.com, tglx@linutronix.de, hca@linux.ibm.com,
	svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org, paulmck@kernel.org,
	rostedt@goodmis.org, x86@kernel.org
Subject: Re: [PATCH v2 04/11] sched: Simplify wake_up_*idle*()
Date: Fri, 22 Oct 2021 15:46:29 +0200	[thread overview]
Message-ID: <ff361300-a390-651d-8316-1f4e8d390af3@samsung.com> (raw)
In-Reply-To: <20210929152428.769328779@infradead.org>

Hi

On 29.09.2021 17:17, Peter Zijlstra wrote:
> Simplify and make wake_up_if_idle() more robust, also don't iterate
> the whole machine with preempt_disable() in it's caller:
> wake_up_all_idle_cpus().
>
> This prepares for another wake_up_if_idle() user that needs a full
> do_idle() cycle.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

This patch landed recently in linux-next as commit 8850cb663b5c ("sched: 
Simplify wake_up_*idle*()"). It causes the following warning on the 
arm64 virt machine under qemu during the system suspend/resume cycle:

--->8---

  printk: Suspending console(s) (use no_console_suspend to debug)

  ============================================
  WARNING: possible recursive locking detected
  5.15.0-rc6-next-20211022 #10905 Not tainted
  --------------------------------------------
  rtcwake/1326 is trying to acquire lock:
  ffffd4e9192e8130 (cpu_hotplug_lock){++++}-{0:0}, at: 
wake_up_all_idle_cpus+0x24/0x98

  but task is already holding lock:
  ffffd4e9192e8130 (cpu_hotplug_lock){++++}-{0:0}, at: 
suspend_devices_and_enter+0x740/0x9f0

  other info that might help us debug this:
   Possible unsafe locking scenario:

         CPU0
         ----
    lock(cpu_hotplug_lock);
    lock(cpu_hotplug_lock);

   *** DEADLOCK ***

   May be due to missing lock nesting notation

  5 locks held by rtcwake/1326:
   #0: ffff54ad86a78438 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x64/0xf0
   #1: ffff54ad84094a88 (&of->mutex){+.+.}-{3:3}, at: 
kernfs_fop_write_iter+0xf4/0x1a8
   #2: ffff54ad83b17a88 (kn->active#43){.+.+}-{0:0}, at: 
kernfs_fop_write_iter+0xfc/0x1a8
   #3: ffffd4e9192efab0 (system_transition_mutex){+.+.}-{3:3}, at: 
pm_suspend+0x214/0x3d0
   #4: ffffd4e9192e8130 (cpu_hotplug_lock){++++}-{0:0}, at: 
suspend_devices_and_enter+0x740/0x9f0

  stack backtrace:
  CPU: 0 PID: 1326 Comm: rtcwake Not tainted 5.15.0-rc6-next-20211022 #10905
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   dump_backtrace+0x0/0x1d0
   show_stack+0x14/0x20
   dump_stack_lvl+0x88/0xb0
   dump_stack+0x14/0x2c
   __lock_acquire+0x171c/0x17b8
   lock_acquire+0x234/0x378
   cpus_read_lock+0x5c/0x150
   wake_up_all_idle_cpus+0x24/0x98
   suspend_devices_and_enter+0x748/0x9f0
   pm_suspend+0x2b0/0x3d0
   state_store+0x84/0x108
   kobj_attr_store+0x14/0x28
   sysfs_kf_write+0x60/0x70
   kernfs_fop_write_iter+0x124/0x1a8
   new_sync_write+0xe8/0x1b0
   vfs_write+0x1d0/0x408
   ksys_write+0x64/0xf0
   __arm64_sys_write+0x14/0x20
   invoke_syscall+0x40/0xf8
   el0_svc_common.constprop.3+0x8c/0x120
   do_el0_svc_compat+0x18/0x48
   el0_svc_compat+0x48/0x100
   el0t_32_sync_handler+0xec/0x140
   el0t_32_sync+0x170/0x174
  OOM killer enabled.
  Restarting tasks ... done.
  PM: suspend exit

--->8---

Let me know if there is anything I can help to debug and fix this issue.

> ---
>   kernel/sched/core.c |   14 +++++---------
>   kernel/smp.c        |    6 +++---
>   2 files changed, 8 insertions(+), 12 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3691,15 +3691,11 @@ void wake_up_if_idle(int cpu)
>   	if (!is_idle_task(rcu_dereference(rq->curr)))
>   		goto out;
>   
> -	if (set_nr_if_polling(rq->idle)) {
> -		trace_sched_wake_idle_without_ipi(cpu);
> -	} else {
> -		rq_lock_irqsave(rq, &rf);
> -		if (is_idle_task(rq->curr))
> -			smp_send_reschedule(cpu);
> -		/* Else CPU is not idle, do nothing here: */
> -		rq_unlock_irqrestore(rq, &rf);
> -	}
> +	rq_lock_irqsave(rq, &rf);
> +	if (is_idle_task(rq->curr))
> +		resched_curr(rq);
> +	/* Else CPU is not idle, do nothing here: */
> +	rq_unlock_irqrestore(rq, &rf);
>   
>   out:
>   	rcu_read_unlock();
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -1170,14 +1170,14 @@ void wake_up_all_idle_cpus(void)
>   {
>   	int cpu;
>   
> -	preempt_disable();
> +	cpus_read_lock();
>   	for_each_online_cpu(cpu) {
> -		if (cpu == smp_processor_id())
> +		if (cpu == raw_smp_processor_id())
>   			continue;
>   
>   		wake_up_if_idle(cpu);
>   	}
> -	preempt_enable();
> +	cpus_read_unlock();
>   }
>   EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);
>   
>
>
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland


  parent reply	other threads:[~2021-10-22 13:46 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 15:17 [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 01/11] sched: Improve try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 02/11] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-29 15:17 ` [PATCH v2 03/11] sched,livepatch: Use task_call_func() Peter Zijlstra
2021-10-05 11:40   ` Petr Mladek
2021-10-05 14:03     ` Peter Zijlstra
2021-10-06  8:59   ` Miroslav Benes
2021-09-29 15:17 ` [PATCH v2 04/11] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-10-13 14:32   ` Qian Cai
2021-10-19  3:47     ` Qian Cai
2021-10-19  8:56       ` Peter Zijlstra
2021-10-19  9:10         ` Peter Zijlstra
2021-10-19 15:32           ` Qian Cai
2021-10-19 15:50             ` Peter Zijlstra
2021-10-19 19:22               ` Qian Cai
2021-10-19 20:27                 ` Peter Zijlstra
     [not found]   ` <CGME20211022134630eucas1p2e79e2816587d182c580459d567c1f2a9@eucas1p2.samsung.com>
2021-10-22 13:46     ` Marek Szyprowski [this message]
2021-09-29 15:17 ` [PATCH v2 05/11] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-10-05 12:00   ` Petr Mladek
2021-10-06  9:16   ` Miroslav Benes
2021-10-07  9:18     ` Vasily Gorbik
2021-10-07 10:02       ` Peter Zijlstra
2021-10-13 19:37   ` Arnd Bergmann
2021-10-14 10:42     ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 06/11] context_tracking: Prefix user_{enter,exit}*() Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 07/11] context_tracking: Add an atomic sequence/state count Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 08/11] context_tracking,rcu: Replace RCU dynticks counter with context_tracking Peter Zijlstra
2021-09-29 18:37   ` Paul E. McKenney
2021-09-29 19:09     ` Peter Zijlstra
2021-09-29 19:11     ` Peter Zijlstra
2021-09-29 19:13     ` Peter Zijlstra
2021-09-29 19:24       ` Peter Zijlstra
2021-09-29 19:45         ` Paul E. McKenney
2021-09-29 18:54   ` Peter Zijlstra
2021-09-29 15:17 ` [RFC][PATCH v2 09/11] context_tracking,livepatch: Dont disturb NOHZ_FULL Peter Zijlstra
2021-10-06  8:12   ` Petr Mladek
2021-10-06  9:04     ` Peter Zijlstra
2021-10-06 10:29       ` Petr Mladek
2021-10-06 11:41         ` Peter Zijlstra
2021-10-06 11:48         ` Miroslav Benes
2021-09-29 15:17 ` [RFC][PATCH v2 10/11] livepatch: Remove klp_synchronize_transition() Peter Zijlstra
2021-10-06 12:30   ` Petr Mladek
2021-09-29 15:17 ` [RFC][PATCH v2 11/11] context_tracking,x86: Fix text_poke_sync() vs NOHZ_FULL Peter Zijlstra
2021-10-21 18:39   ` Marcelo Tosatti
2021-10-21 18:40     ` Marcelo Tosatti
2021-10-21 19:25     ` Peter Zijlstra
2021-10-21 19:57       ` Marcelo Tosatti
2021-10-21 20:18         ` Peter Zijlstra
2021-10-26 18:19           ` Marcelo Tosatti
2021-10-26 19:38             ` Peter Zijlstra
2021-09-29 18:03 ` [PATCH v2 00/11] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL Paul E. McKenney

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