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SubjectRe: configfs: Q: item leak in a failing configfs_attach_group()?
On Wed, Jun 25, 2008 at 11:55:27AM +0200, Louis Rilling wrote:
> On Tue, Jun 24, 2008 at 02:34:39PM -0700, Joel Becker wrote:
> > On Tue, Jun 24, 2008 at 08:04:56PM +0200, Louis Rilling wrote:
> > > On Tue, Jun 24, 2008 at 10:10:51AM -0700, Joel Becker wrote:
> > > > On Tue, Jun 24, 2008 at 04:16:49PM +0200, Louis Rilling wrote:
> > > > > Hi,
> > > > >
> > > > > I'd like an opinion on the following scenario:
> > > > >
> > > > > process 1: process 2:
> > > > > configfs_mkdir("A")
> > > > > attach_group("A")
> > > > > attach_item("A")
> > > > > d_instantiate("A")
> > > > > populate_groups("A")
> > > > > mutex_lock("A")
> > > > > attach_group("A/B")
> > > > > attach_item("A")
> > > > > d_instantiate("A/B")
> > > > > mkdir("A/B/C")
> > > > > do_path_lookup("A/B/C", LOOKUP_PARENT)
> > > >
> > > > This has to sleep until
> > > > configfs_mkdir("A") finishes.
> > > > It's waiting on A->d_parent's
> > > > i_mutex, which is held by
> > > > sys_mkdirat().
> > >
> > > Can you be more precise? I don't see where do_path_lookup() locks an inode
> >
> > It doesn't. It's in lookup_create(), which takes the mutex on the
> > parent of 'A'. Note that the end of sys_mkdirat() explicitly drops that
> > mutex - it couldn't do so if it hadn't been taken :-)
>
> So, my scenario is realistic. Process 2 only locks "B"'s inode in
> lookup_create() ("B" is the parent of the new directory "C"), and never has to
> lock "A" or "A"'s parent. IOW, process 2 does not have to wait on any i_mutex
> locked by process 1.

Um, 'A' hasn't appeared yet. I don't see how it looks up 'A'
until we're done.

Joel

--

"When ideas fail, words come in very handy."
- Goethe

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127


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