linux-kernel - Re: [PATCH block/for-6.2-fixes] block: Drop spurious might_sleep() from blk_put

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Date:   Fri, 6 Jan 2023 12:45:12 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Dan Carpenter <error27@...il.com>,
        Christoph Hellwig <hch@....de>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH block/for-6.2-fixes] block: Drop spurious might_sleep()
 from blk_put_queue()

On Fri, Jan 06, 2023 at 10:34:10AM -1000, Tejun Heo wrote:
> Dan reports the following smatch detected the following:
> 
>   block/blk-cgroup.c:1863 blkcg_schedule_throttle() warn: sleeping in atomic context
> 
> caused by blkcg_schedule_throttle() calling blk_put_queue() in an
> non-sleepable context.
> 
> blk_put_queue() acquired might_sleep() in 63f93fd6fa57 ("block: mark
> blk_put_queue as potentially blocking") which transferred the might_sleep()
> from blk_free_queue().
> 
> blk_free_queue() acquired might_sleep() in e8c7d14ac6c3 ("block: revert back
> to synchronous request_queue removal") while turning request_queue removal
> synchronous. However, this isn't necessary as nothing in the free path
> actually requires sleeping.
> 
> It's pretty unusual to require a sleeping context in a put operation and
> it's not needed in the first place. Let's drop it.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://lkml.kernel.org/r/Y7g3L6fntnTtOm63@kili
> Cc: Christoph Hellwig <hch@....de>
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Fixes: e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal") # v5.9+

*tons* has changed since e8c7d14ac6c3 and so the bots might think that
*if* this patch is applied upstream it is justified for older kernels
and I don't think that's yet been verified and doubt it.

And so I think adding a "Fixes" tag is not appropriate here.

First I'd like to hear from Christoph if he agrees with this patch
upstream. For stable, someone would have to do the homework.

  Luis