From: Al Viro <viro@ZenIV.linux.org.uk>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
hch@infradead.org, torvalds@linux-foundation.org,
Trond.Myklebust@netapp.com
Subject: Re: [PATCH 1/2] vfs: dcache: fix deadlock in tree traversal
Date: Mon, 17 Sep 2012 21:39:47 +0100 [thread overview]
Message-ID: <20120917203946.GV13973@ZenIV.linux.org.uk> (raw)
In-Reply-To: <871ui01jr1.fsf@tucsk.pomaz.szeredi.hu>
On Mon, Sep 17, 2012 at 10:23:30PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@suse.cz>
>
> IBM reported a deadlock in select_parent(). This was found to be caused by
> taking rename_lock when already locked when restarting the tree traversal.
>
> There are two cases when the traversal needs to be restarted:
>
> 1) concurrent d_move(); this can only happen when not already locked,
> since taking rename_lock protects against concurrent d_move().
>
> 2) racing with final d_put() on child just at the moment of ascending
> to parent; rename_lock doesn't protect against this rare race, so it
> can happen when already locked.
>
> Because of case 2. we need to be able to handle restarting the traversal
> when rename_lock is already held. This patch fixes all three callers of
> try_to_ascend().
>
> IBM reported that the deadlock is gone with this patch. However, there's still
> a soft lockup which is addressed by the next patch.
Egads... The problem is real and analysis, AFAICS, is correct, but result
is extremely ugly ;-/ Let me try to come up with something saner; I'll
push that one to Linus if nothing better comes to mind, but I'd really
prefer to avoid adding to ugliness in fs/dcache.c - we already have too
much of that...
next prev parent reply other threads:[~2012-09-17 20:39 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-17 20:23 [PATCH 1/2] vfs: dcache: fix deadlock in tree traversal Miklos Szeredi
2012-09-17 20:31 ` [PATCH 2/2] vfs: dcache: use DCACHE_DENTRY_KILLED instead of DCACHE_DISCONNECTED in d_kill() Miklos Szeredi
2012-09-17 20:39 ` Al Viro [this message]
2012-09-17 22:09 ` [PATCH 1/2] vfs: dcache: fix deadlock in tree traversal Linus Torvalds
2012-09-18 14:53 ` Miklos Szeredi
2012-09-18 15:56 ` Linus Torvalds
2012-09-18 16:27 ` Miklos Szeredi
2012-09-18 18:22 ` Linus Torvalds
2012-09-18 20:35 ` [PATCH] trivial select_parent documentation fix J. Bruce Fields
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