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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Tejun Heo <tj@kernel.org>
Cc: 0day robot <lkp@intel.com>, LKML <linux-kernel@vger.kernel.org>,
	lkp@lists.01.org, kernel test robot <oliver.sang@intel.com>
Subject: Re: [PATCH] workqueue: Use private WQ for schedule_on_each_cpu() API
Date: Wed, 23 Feb 2022 09:57:27 +0900	[thread overview]
Message-ID: <16a33a65-3c67-ef66-ccc8-9c4fffb0ae5a@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <YhUdjip4VSWe4zDO@slm.duckdns.org>

On 2022/02/23 2:29, Tejun Heo wrote:
> On Mon, Feb 21, 2022 at 07:38:09PM +0900, Tetsuo Handa wrote:
>> Since schedule_on_each_cpu() calls schedule_work_on() and flush_work(),
>> we should avoid using system_wq in order to avoid unexpected locking
>> dependency.
> 
> I don't get it. schedule_on_each_cpu() is flushing each work item and thus
> shouldn't need its own flushing domain. What's this change for?

A kernel test robot tested "[PATCH v2] workqueue: Warn flush attempt using
system-wide workqueues" on 5.16.0-06523-g29bd199e4e73 and hit a lockdep
warning ( https://lkml.kernel.org/r/20220221083358.GC835@xsang-OptiPlex-9020 ).

Although the circular locking dependency itself needs to be handled by
lockless console printing support, we won't be able to apply
"[PATCH v2] workqueue: Warn flush attempt using system-wide workqueues"
if schedule_on_each_cpu() continues using system-wide workqueues.


WARNING: multiple messages have this Message-ID (diff)
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: lkp@lists.01.org
Subject: Re: [PATCH] workqueue: Use private WQ for schedule_on_each_cpu() API
Date: Wed, 23 Feb 2022 09:57:27 +0900	[thread overview]
Message-ID: <16a33a65-3c67-ef66-ccc8-9c4fffb0ae5a@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <YhUdjip4VSWe4zDO@slm.duckdns.org>

[-- Attachment #1: Type: text/plain, Size: 927 bytes --]

On 2022/02/23 2:29, Tejun Heo wrote:
> On Mon, Feb 21, 2022 at 07:38:09PM +0900, Tetsuo Handa wrote:
>> Since schedule_on_each_cpu() calls schedule_work_on() and flush_work(),
>> we should avoid using system_wq in order to avoid unexpected locking
>> dependency.
> 
> I don't get it. schedule_on_each_cpu() is flushing each work item and thus
> shouldn't need its own flushing domain. What's this change for?

A kernel test robot tested "[PATCH v2] workqueue: Warn flush attempt using
system-wide workqueues" on 5.16.0-06523-g29bd199e4e73 and hit a lockdep
warning ( https://lkml.kernel.org/r/20220221083358.GC835(a)xsang-OptiPlex-9020 ).

Although the circular locking dependency itself needs to be handled by
lockless console printing support, we won't be able to apply
"[PATCH v2] workqueue: Warn flush attempt using system-wide workqueues"
if schedule_on_each_cpu() continues using system-wide workqueues.

  reply	other threads:[~2022-02-23  0:57 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-21  8:33 [workqueue] 29bd199e4e: WARNING:possible_circular_locking_dependency_detected kernel test robot
2022-02-21  8:33 ` kernel test robot
2022-02-21 10:38 ` [PATCH] workqueue: Use private WQ for schedule_on_each_cpu() API Tetsuo Handa
2022-02-21 10:38   ` Tetsuo Handa
2022-02-22 17:29   ` Tejun Heo
2022-02-22 17:29     ` Tejun Heo
2022-02-23  0:57     ` Tetsuo Handa [this message]
2022-02-23  0:57       ` Tetsuo Handa
2022-02-23 21:33       ` Tejun Heo
2022-02-23 21:33         ` Tejun Heo
2022-02-23 22:26         ` Tetsuo Handa
2022-02-23 22:26           ` Tetsuo Handa
2022-02-23 22:29           ` Tejun Heo
2022-02-23 22:29             ` Tejun Heo
2022-02-28 14:03             ` [PATCH v3] workqueue: Warn flushing of kernel-global workqueues Tetsuo Handa
2022-02-28 14:03               ` Tetsuo Handa
2022-02-28 18:42               ` Tejun Heo
2022-02-28 18:42                 ` Tejun Heo
2022-03-17 22:25                 ` Tetsuo Handa
2022-03-17 22:25                   ` Tetsuo Handa

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