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 13:52:21 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Luis Chamberlain <mcgrof@...nel.org>, Tejun Heo <tj@...nel.org>
Cc:     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 1/6/23 1:45 PM, Luis Chamberlain wrote:
> 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.

Outside of the easily audited paths, the kobj release paths are the
only ones of concern. And I didn't spot anything that sleeps. Looks
fine to me.

-- 
Jens Axboe