From: Eric Biggers <ebiggers3@gmail.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-btrfs@vger.kernel.org, Chris Mason <clm@fb.com>,
linux-fsdevel@vger.kernel.org
Subject: Re: d_instantiate() and unlock_new_inode() order in btrfs_mkdir()
Date: Wed, 18 Apr 2018 17:54:03 -0700 [thread overview]
Message-ID: <20180419005403.GA946@sol.localdomain> (raw)
In-Reply-To: <20180419001559.GG30522@ZenIV.linux.org.uk>
On Thu, Apr 19, 2018 at 01:15:59AM +0100, Al Viro wrote:
> On Thu, Apr 19, 2018 at 01:06:13AM +0100, Al Viro wrote:
> > On Wed, Apr 18, 2018 at 05:00:29PM -0700, Eric Biggers wrote:
> > > Hi Chris and other btrfs folks,
> > >
> > > btrfs_mkdir() calls d_instantiate() before unlock_new_inode(), which is wrong
> > > because it exposes the inode to lookups before it's been fully initialized.
> >
> > Huh? It *is* fully initialized by that point; what else is left to do?
>
> ISTR something about false positives from lockdep (with
> lockdep_annotate_inode_mutex_key() called too late, perhaps?); said that, it
> was a long time ago and I don't remember details at the moment... Are you
> actually seeing a deadlock there or is that just lockdep complaining?
It's an actual deadlock. unlock_new_inode() calls
lockdep_annotate_inode_mutex_key() which calls init_rwsem(), which resets
i_rwsem->count while it's read-locked by lookup_slow(). Then the unlock in
lookup_slow() makes i_rwsem->count negative, which makes it appear to be
write-locked.
So no, the inode isn't fully initialized until unlock_new_inode() ran.
Eric
prev parent reply other threads:[~2018-04-19 0:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-19 0:00 d_instantiate() and unlock_new_inode() order in btrfs_mkdir() Eric Biggers
2018-04-19 0:06 ` Al Viro
2018-04-19 0:15 ` Al Viro
2018-04-19 0:54 ` Eric Biggers [this message]
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