linux-kernel - Re: processes hung after sys_renameat, and 'missing' processes

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Message-ID: <20120607015410.GG30000@ZenIV.linux.org.uk>
Date:	Thu, 7 Jun 2012 02:54:10 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: processes hung after sys_renameat, and 'missing' processes

On Wed, Jun 06, 2012 at 06:45:35PM -0700, Linus Torvalds wrote:
> On Wed, Jun 6, 2012 at 6:31 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > And you want to check i_mutex on old parent, not the file being moved
> > itself. ?IOW, the second one should be
> >
> > if (dentry->d_parent != dentry)
> > ? ? ? ?WARN_ON_ONCE(!mutex_is_locked(&dentry->d_parent->d_inode->i_mutex));
> 
> Do you even need the "dentry->d_parent != dentry" test? When do we
> even rename root dentries?

Root of the filesystem - never; root of disconnected subtree - sure,
that's how they become connected to the tree.  See d_materialize_unique(),
for example...

BTW, I really need more coffee - those checks belong in __d_move(),
not d_move(); aforementioned d_materialize_unique() doesn't use d_move(),
it calls __d_move() directly.  Sorry.
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