linux-kernel - Re: [PATCH workqueue/for-6.10-fixes] workqueue: Refactor worker ID formatting and make wq_worker

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Date: Thu, 23 May 2024 09:16:49 +0200
From: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
 Yafang Shao <laoar.shao@...il.com>
Cc: Tejun Heo <tj@...nel.org>, Jan Engelhardt <jengelh@...i.de>,
 Craig Small <csmall@....com.au>, linux-kernel@...r.kernel.org,
 Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH workqueue/for-6.10-fixes] workqueue: Refactor worker ID
 formatting and make wq_worker_comm() use full ID string

On 21/05/2024 20.05, Linus Torvalds wrote:
> On Mon, 20 May 2024 at 19:34, Yafang Shao <laoar.shao@...il.com> wrote:
>>
>> We discussed extending it to 24 characters several years ago [0], but
>> some userspace tools might break.
> 
> Well, the fact that we already expose names longer than 16 bytes in
> /proc means that at least *that* side of it could use an extended
> comm[] array.
> 
> Yes, some other interfaces might want to still use a 16-byte limit as
> the length for the buffers they use (tracing?) but I suspect we could
> make the comm[] array easily bigger.
> 
> But what I suspect we should do *first* is to try to get rid of a lot
> of the "current->comm" users. One of the most common uses is purely
> for printing, and we could actually just add a new '%p' pointer for
> printing the current name. That would allow our vsprintf() code to not
> just use tsk->comm, but to use the full_name for threads etc.
> 
> So instead of
> 
>    printf("%s ..", tsk->comm..);
> 
> we could have something like
> 
>    printf("%pc ..", tsk);

The alphabet is running out of letters, so if somebody goes and
implement this, I'd suggest making this %pc thing take extra modifiers,
so one could also get the pid or whatever else one might want to print
from a task. I.e. %pcN, %pcP, ... We could of course have %pc with no
following letter mean ->comm (or "real name" for kernel threads) if that
is the most common thing, which it very well might be.

Rasmus