linux-kernel - Re: [PATCH] workqueue: don't skip lockdep wq dependency in cancel_work

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Message-ID: <7d034f7b-af42-4dbc-0887-60f4bdb3dcca@I-love.SAKURA.ne.jp>
Date:   Fri, 29 Jul 2022 11:49:51 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Johannes Berg <johannes.berg@...el.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] workqueue: don't skip lockdep wq dependency in
 cancel_work_sync()

On 2022/07/29 11:28, Tetsuo Handa wrote:
> Thinking more, I might be confused by difference between
> 
>   the lockdep "struct work_struct" dependency handling

the lockdep "struct workqueue_struct" dependency handling

> 
> and
> 
>   the lockdep "struct work" dependency handling

the lockdep "struct work_struct" dependency handling


On 2022/07/29 11:38, Lai Jiangshan wrote:
> The commit fd1a5b04dfb8("workqueue: Remove now redundant lock
> acquisitions wrt. workqueue flushes") removed this lockdep check.
> 
> And the commit 87915adc3f0a("workqueue: re-add lockdep
> dependencies for flushing") added it back for non-canceling cases.
> 
> It seems the commit fd1a5b04dfb8 is the culprit and 87915adc3f0a
> didn't fixes all the problem of it.
> 
> So it is better to complete 87915adc3f0a by making __flush_work()
> does lock_map_acquire(&work->lockdep_map) for both canceling and
> non-canceling cases.

Yes, commit 87915adc3f0acdf0 was incomplete.