Re: processes hung after sys_renameat, and 'missing' processes

From: Al Viro
Date: Wed Jun 06 2012 - 21:31:46 EST


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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