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

[Luis Henriques]

Ian Kent <raven at themaw.net> writes:

> On Wed, 2014-05-14 at 15:57 +0100, Luis Henriques wrote:
>> This is a note to let you know that I have just added a patch titled
>> 
>>     autofs: fix lockref lookup
>> 
>> to the linux-3.11.y-queue branch of the 3.11.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-3.11.y-queue
>> 
>> If you, or anyone else, feels it should not be added to this tree, please 
>> reply to this email.
>
> 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.
>  

Great, thanks for your review.  I'll just drop this patch from the
3.11 kernel queue.

Cheers,
-- 
Luís

>> 
>> For more information about the 3.11.y.z tree, see
>> https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
>> 
>> Thanks.
>> -Luis
>> 
>> ------
>> 
>> From 506be3083ae3126309bc58ec3452a64bc9a09146 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>
>> Signed-off-by: Luis Henriques <luis.henriques 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 92ef341..2a69bde 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 (!d_count(active))
>> +		if ((int) d_count(active) <= 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
>>