linux-kernel - Re: [PATCH v2] workqueue: warn if delayed

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Message-ID: <Z4FoF8471fQSHPXm@slm.duckdns.org>
Date: Fri, 10 Jan 2025 08:33:59 -1000
From: Tejun Heo <tj@...nel.org>
To: Imran Khan <imran.f.khan@...cle.com>
Cc: jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] workqueue: warn if delayed_work is queued to an
 offlined cpu.

On Fri, Jan 10, 2025 at 10:27:11AM +1100, Imran Khan wrote:
> delayed_work submitted to an offlined cpu, will not get executed,
> after the specified delay if the cpu remains offline. If the cpu
> never comes online the work will never get executed.
> checking for online cpu in __queue_delayed_work, does not sound
> like a good idea because to do this reliably we need hotplug lock
> and since work may be submitted from atomic contexts, we would
> have to use cpus_read_trylock. But if trylock fails we would queue
> the work on any cpu and this may not be optimal because our intended
> cpu might still be online.
> 
> Putting a WARN_ON_ONCE for an already offlined cpu, will indicate users
> of queue_delayed_work_on, if they are (wrongly) trying to queue
> delayed_work on offlined cpu. Also indicate the problem of using
> offlined cpu with queue_delayed_work_on, in its description.
> 
> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>

Applied to wq/for-6.13-fixes.

Thanks.

-- 
tejun