linux-kernel - Re: REGRESSION/TEST FAILURE caused by DEBUG

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Message-ID: <5670badd-0268-8a06-6612-b58eb6a304b6@redhat.com>
Date:   Wed, 4 Apr 2018 09:55:18 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>
Subject: Re: REGRESSION/TEST FAILURE caused by DEBUG_RWSEMS

On 04/04/2018 09:23 AM, Theodore Y. Ts'o wrote:
> The commit 5149cbac4235: "locking/rwsem: Add DEBUG_RWSEMS to look for
> lock/unlock emismatches" (newly added in this merge window) will cause
> xfstests tests failures in generic/068 for all file systems.
>
> This is because the freeze and thaw ioctls, by design, are run in
> different processes.  It looks like the concern for why
> CONFIG_DEBUG_RWSEMS was added is because read/write semaphores can
> spin --- which if the case, we need to make sure that (a) the spinlock
> code path is not used for the freeze/thaw ioctls, and (b) we don't
> trigger the debug WARN_ON.
>
> Cheers,
>
The rwsem code has an up_read_non_owner() function for this kind of
cross task lock/unlock. I think we should add the corresponding
up_write_non_owner() for that. It is better to annotate those calls that
have this issue rather than working around it. I will post a patch to
address that later today.

Cheers,
Longman