linux-ext4 - Re: [PATCH] jbd2: Fix lockdep splat with generic/270 test

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Date:   Sat, 29 Apr 2017 20:28:17 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] jbd2: Fix lockdep splat with generic/270 test

On Tue, Apr 11, 2017 at 03:46:44PM +0200, Jan Kara wrote:
> I've hit a lockdep splat with generic/270 test complaining that:
> 
> 3216.fsstress.b/3533 is trying to acquire lock:
>  (jbd2_handle){++++..}, at: [<ffffffff813152e0>] jbd2_log_wait_commit+0x0/0x150
> 
> but task is already holding lock:
>  (jbd2_handle){++++..}, at: [<ffffffff8130bd3b>] start_this_handle+0x35b/0x850
> 
> The underlying problem is that jbd2_journal_force_commit_nested()
> (called from ext4_should_retry_alloc()) may get called while a
> transaction handle is started. In such case it takes care to not wait
> for commit of the running transaction (which would deadlock) but only
> for a commit of a transaction that is already committing (which is safe
> as that doesn't wait for any filesystem locks).
> 
> In fact there are also other callers of jbd2_log_wait_commit() that take
> care to pass tid of a transaction that is already committing and for
> those cases, the lockdep instrumentation is too restrictive and leading
> to false positive reports. Fix the problem by calling
> jbd2_might_wait_for_commit() from jbd2_log_wait_commit() only if the
> transaction isn't already committing.
> 
> Fixes: 1eaa566d368b214d99cbb973647c1b0b8102a9ae
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.

						- Ted