[3.8.y.z extended stable] Patch "autofs: fix lockref lookup" has been added to staging queue

[Kamal Mostafa]

On Tue, 2014-06-17 at 10:03 +0800, Ian Kent wrote:
> On Mon, 2014-06-16 at 16:44 -0700, Kamal Mostafa wrote:
> > This is a note to let you know that I have just added a patch titled
> > 
> >     autofs: fix lockref lookup
> > 
> > to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
> > which can be found at:
> > 
> >  http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue
> > 
> > This patch is scheduled to be released in version 3.8.13.24.
> > 
> > If you, or anyone else, feels it should not be added to this tree, please 
> > reply to this email.
> 
> Looks the same applies here as it did for 3.11.y.z.
> Here's what I said then.
> 
> "AFAICS lockref_mark_dead() isn't present in this tree so the bug the
> patch fixes isn't present.
> 
> I don't think it will introduce a regression and will be there if the
> later lockref change is added at some point.
> 
> So I guess it's your choice whether to keep it or not."


Yup.  I'll drop this one from the 3.8-stable queue.

Thanks very much, Ian!

 -Kamal


> > 
> > For more information about the 3.8.y.z tree, see
> > https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
> > 
> > Thanks.
> > -Kamal
> > 
> > ------
> > 
> > From 808d767f6f0e237b6f02c62ca81dab0960f948e9 Mon Sep 17 00:00:00 2001
> > From: Ian Kent <raven at themaw.net>
> > Date: Tue, 6 May 2014 12:50:06 -0700
> > Subject: autofs: fix lockref lookup
> > 
> > commit 6b6751f7feba68d8f5c72b72cc69a1c5a625529c upstream.
> > 
> > autofs needs to be able to see private data dentry flags for its dentrys
> > that are being created but not yet hashed and for its dentrys that have
> > been rmdir()ed but not yet freed.  It needs to do this so it can block
> > processes in these states until a status has been returned to indicate
> > the given operation is complete.
> > 
> > It does this by keeping two lists, active and expring, of dentrys in
> > this state and uses ->d_release() to keep them stable while it checks
> > the reference count to determine if they should be used.
> > 
> > But with the recent lockref changes dentrys being freed sometimes don't
> > transition to a reference count of 0 before being freed so autofs can
> > occassionally use a dentry that is invalid which can lead to a panic.
> > 
> > Signed-off-by: Ian Kent <raven at themaw.net>
> > Cc: Al Viro <viro at zeniv.linux.org.uk>
> > Cc: Linus Torvalds <torvalds at linux-foundation.org>
> > Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> > Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> > [ kamal: backport to 3.8-stable: context ]
> > Signed-off-by: Kamal Mostafa <kamal at canonical.com>
> > ---
> >  fs/autofs4/root.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
> > index c934476..48f16ab 100644
> > --- a/fs/autofs4/root.c
> > +++ b/fs/autofs4/root.c
> > @@ -179,7 +179,7 @@ static struct dentry *autofs4_lookup_active(struct dentry *dentry)
> >  		spin_lock(&active->d_lock);
> > 
> >  		/* Already gone? */
> > -		if (active->d_count == 0)
> > +		if ((int) active->d_count <= 0)
> >  			goto next;
> > 
> >  		qstr = &active->d_name;
> > @@ -230,7 +230,7 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)
> > 
> >  		spin_lock(&expiring->d_lock);
> > 
> > -		/* Bad luck, we've already been dentry_iput */
> > +		/* We've already been dentry_iput or unlinked */
> >  		if (!expiring->d_inode)
> >  			goto next;
> > 
> > --
> > 1.9.1
> > 
> 
>