linux-kernel - Re: drivers/md/dm-vdo/data-vio.c:976 vdo_launch_bio() warn: inconsistent returns '&pool->lock'.

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Message-ID: <1c0beb9b-6b90-4c92-a4f3-f228dc0aa527@redhat.com>
Date: Tue, 29 Oct 2024 13:03:35 -0400
From: Matthew Sakai <msakai@...hat.com>
To: Dan Carpenter <dan.carpenter@...aro.org>, Philip Li <philip.li@...el.com>
Cc: oe-kbuild@...ts.linux.dev, Mike Snitzer <snitzer@...nel.org>,
 lkp@...el.com, oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: drivers/md/dm-vdo/data-vio.c:976 vdo_launch_bio() warn:
 inconsistent returns '&pool->lock'.

Okay. Just to restate, what I took away from this thread is
1) The current code provokes a warning.
2) When bisecting, the bot found a (different) warning from the patch 
introducing this code, and so the mail points out that warning instead 
of the warning in newer code.
3) The warning is showing up now because new checking allows the bot to 
notice problems it didn't notice before.

The commit I cited fixed warning from sparse, but I don't think we 
looked at smatch. This particular code does not have a locking problem, 
but the way it's spelled makes it difficult for static tools to 
understand that there is not a problem. I'll take a look and see if 
there's anything further I can do address the actual current warning.

Thanks for your explanation. I think I have a much better understanding 
of what this bot it doing now, I'll keep it in mind when we get warning 
in the future.

Matt

On 10/29/24 4:19 AM, Dan Carpenter wrote:
> On Tue, Oct 29, 2024 at 11:07:07AM +0300, Dan Carpenter wrote:
>> 3) The kbuild bot detected the bug, but unfortunately the cross function DB
>>     doesn't scale well enough for the kbuild bot to use so it didn't detect the
>>     fix.
> 
> Aw crud.  It does still print a warning on linux-next actually.
> Smatch says that we lock "&pool->lock" and unlocked
> "&pool->discard_limiter->pool->lock".
> 
> Anyway.  Points 1 and 4 that we were running new checks on old code and that
> the code in the email did have a bug are correct.
> 
> regards,
> dan carpenter
>