From: NeilBrown <neilb@suse.com>
To: Jeff Layton <jlayton@kernel.org>, linux-fsdevel@vger.kernel.org
Cc: bfields@fieldses.org, asn@redhat.com
Subject: Re: [PATCH v3] locks: wake any locks blocked on request before deadlock check
Date: Tue, 26 Mar 2019 09:33:47 +1100 [thread overview]
Message-ID: <87k1gm4m9g.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20190325123252.10211-1-jlayton@kernel.org>
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On Mon, Mar 25 2019, Jeff Layton wrote:
> Andreas reported that he was seeing the tdbtorture test fail in some
> cases with -EDEADLCK when it wasn't before. Some debugging showed that
> deadlock detection was sometimes discovering the caller's lock request
> itself in a dependency chain.
>
> While we remove the request from the blocked_lock_hash prior to
> reattempting to acquire it, any locks that are blocked on that request
> will still be present in the hash and will still have their fl_blocker
> pointer set to the current request.
>
> This causes posix_locks_deadlock to find a deadlock dependency chain
> when it shouldn't, as a lock request cannot block itself.
>
> We are going to end up waking all of those blocked locks anyway when we
> go to reinsert the request back into the blocked_lock_hash, so just do
> it prior to checking for deadlocks. This ensures that any lock blocked
> on the current request will no longer be part of any blocked request
> chain.
>
> URL: https://bugzilla.kernel.org/show_bug.cgi?id=202975
> Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.")
> Cc: stable@vger.kernel.org
> Reported-by: Andreas Schneider <asn@redhat.com>
> Signed-off-by: Neil Brown <neilb@suse.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
Yes, I'm happy with this patch and description.
It is more "obviously correct" than the other patch.
Thanks,
NeilBrown
> ---
> fs/locks.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index eaa1cfaf73b0..71d0c6c2aac5 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> */
> error = -EDEADLK;
> spin_lock(&blocked_lock_lock);
> + /*
> + * Ensure that we don't find any locks blocked on this
> + * request during deadlock detection.
> + */
> + __locks_wake_up_blocks(request);
> if (likely(!posix_locks_deadlock(request, fl))) {
> error = FILE_LOCK_DEFERRED;
> __locks_insert_block(fl, request,
> --
> 2.20.1
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next prev parent reply other threads:[~2019-03-25 22:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-21 11:27 [PATCH] locks: ignore same lock in blocked_lock_hash Jeff Layton
2019-03-21 21:51 ` NeilBrown
2019-03-22 0:42 ` J. Bruce Fields
2019-03-22 1:58 ` NeilBrown
2019-03-22 20:27 ` J. Bruce Fields
2019-03-23 12:08 ` [PATCH v2] " Jeff Layton
2019-03-24 0:51 ` NeilBrown
2019-03-25 12:31 ` Jeff Layton
2019-03-25 12:32 ` [PATCH v3] locks: wake any locks blocked on request before deadlock check Jeff Layton
2019-03-25 22:09 ` J. Bruce Fields
2019-03-25 22:33 ` NeilBrown [this message]
2019-03-23 12:05 ` [PATCH] locks: ignore same lock in blocked_lock_hash Jeff Layton
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