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

[Ian Kent]

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."

> 
> 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
>