From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Tejun Heo <tj@kernel.org>
Cc: kernel test robot <lkp@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
linux-kernel@vger.kernel.org, LKP <lkp@lists.01.org>,
Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH v2] workqueue: Remove the warning in wq_worker_sleeping()
Date: Fri, 3 Apr 2020 21:29:02 +0200 [thread overview]
Message-ID: <20200403192902.ws33fhs5mrxg6dvo@linutronix.de> (raw)
In-Reply-To: <20200403145326.GA162390@mtj.duckdns.org>
On 2020-04-03 10:53:26 [-0400], Tejun Heo wrote:
> Hello,
Hello Tejun,
> This is not a usual control flow, right?
The worker is blocked on something and while invoking schedule() it
needs to be preempted by an interrupt which opens interrupts and invokes
schedule() as well.
Interrupt handler are not allowed to enable interrupts in general.
Page-fault handler do so by they happen only while the calling context
triggered a page-fault. Since the kernel is always mapped, this does not
happen.
The async page fault handler is any exception here. I don't find
anything else while looking over x86's idtentry. So this makes it highly
unusual control flow, yes.
> Can we annotate this case specifically
> instead of weakening santiy check for generic cases?
puh. So if this
do_async_page_fault() -> do_page_fault()
never happens but only
do_async_page_fault() -> kvm_async_pf_task_wait()
then kvm_async_pf_task_wait() could invoke preempt_schedule() instead.
This would avoid the worker part (and the warning) but is only available
for PREEMPTION kernels. And I think the former case might happen.
> Thanks.
>
Sebastian
WARNING: multiple messages have this Message-ID (diff)
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: lkp@lists.01.org
Subject: Re: [PATCH v2] workqueue: Remove the warning in wq_worker_sleeping()
Date: Fri, 03 Apr 2020 21:29:02 +0200 [thread overview]
Message-ID: <20200403192902.ws33fhs5mrxg6dvo@linutronix.de> (raw)
In-Reply-To: <20200403145326.GA162390@mtj.duckdns.org>
[-- Attachment #1: Type: text/plain, Size: 1163 bytes --]
On 2020-04-03 10:53:26 [-0400], Tejun Heo wrote:
> Hello,
Hello Tejun,
> This is not a usual control flow, right?
The worker is blocked on something and while invoking schedule() it
needs to be preempted by an interrupt which opens interrupts and invokes
schedule() as well.
Interrupt handler are not allowed to enable interrupts in general.
Page-fault handler do so by they happen only while the calling context
triggered a page-fault. Since the kernel is always mapped, this does not
happen.
The async page fault handler is any exception here. I don't find
anything else while looking over x86's idtentry. So this makes it highly
unusual control flow, yes.
> Can we annotate this case specifically
> instead of weakening santiy check for generic cases?
puh. So if this
do_async_page_fault() -> do_page_fault()
never happens but only
do_async_page_fault() -> kvm_async_pf_task_wait()
then kvm_async_pf_task_wait() could invoke preempt_schedule() instead.
This would avoid the worker part (and the warning) but is only available
for PREEMPTION kernels. And I think the former case might happen.
> Thanks.
>
Sebastian
next prev parent reply other threads:[~2020-04-03 19:29 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 7:43 6d25be5782 ("sched/core, workqueues: Distangle worker .."): [ 52.816697] WARNING: CPU: 0 PID: 14 at kernel/workqueue.c:882 wq_worker_sleeping kernel test robot
2020-03-27 7:43 ` kernel test robot
2020-03-27 17:53 ` [PATCH] workqueue: Don't double assign worker->sleeping Sebastian Andrzej Siewior
2020-03-27 17:53 ` Sebastian Andrzej Siewior
2020-03-27 23:29 ` [PATCH v2] workqueue: Remove the warning in wq_worker_sleeping() Sebastian Andrzej Siewior
2020-03-27 23:29 ` Sebastian Andrzej Siewior
2020-04-03 14:53 ` Tejun Heo
2020-04-03 14:53 ` Tejun Heo
2020-04-03 19:29 ` Sebastian Andrzej Siewior [this message]
2020-04-03 19:29 ` Sebastian Andrzej Siewior
2020-04-03 17:45 ` Daniel Jordan
2020-04-03 17:45 ` Daniel Jordan
2020-04-03 18:25 ` Sebastian Andrzej Siewior
2020-04-03 18:25 ` Sebastian Andrzej Siewior
2020-04-03 19:05 ` Daniel Jordan
2020-04-03 19:05 ` Daniel Jordan
2020-04-01 3:22 ` [PATCH] workqueue: Don't double assign worker->sleeping Lai Jiangshan
2020-04-01 3:44 ` Lai Jiangshan
2020-04-01 13:03 ` Sebastian Andrzej Siewior
2020-04-01 13:03 ` Sebastian Andrzej Siewior
2020-04-02 0:07 ` Lai Jiangshan
2020-04-02 7:29 ` Sebastian Andrzej Siewior
2020-04-02 7:29 ` Sebastian Andrzej Siewior
2020-04-08 12:20 ` [tip: sched/urgent] workqueue: Remove the warning in wq_worker_sleeping() tip-bot2 for Sebastian Andrzej Siewior
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