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

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Message-ID: <20120607013149.GF30000@ZenIV.linux.org.uk>
Date:	Thu, 7 Jun 2012 02:31:49 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Thu, Jun 07, 2012 at 02:29:00AM +0100, Al Viro wrote:
> On Wed, Jun 06, 2012 at 09:19:15PM -0400, Dave Jones wrote:
> > On Wed, Jun 06, 2012 at 05:42:35PM -0700, Linus Torvalds wrote:
> > 
> >  > So Al meant you to test mutex_is_locked(dentry->d_inode->i_mutex) of
> >  > the parents.
> > 
> > ok, I ended up with..
> > 
> >         WARN_ON_ONCE(!mutex_is_locked(&target->d_parent->d_inode->i_mutex));
> > 
> >         if (dentry->d_parent != NULL)
> 			       != dentry)
> 
> ->d_parent *never* should be NULL; when dentry is disconnected from the
> tree (or hadn't been connected to it yet), it points to that dentry itself.

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));
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