[PATCH] return ENOENT from ext3_link when racing with unlink

[PATCH] return ENOENT from ext3_link when racing with unlink

[Eric Sandeen]

An update from the earlier thread, 
[PATCH] [RFC] remove ext3 inode from orphan list when link and unlink race

I think this is better than the original idea of trying to handle the race;
I've seen that the orphan inode list can get corrupted, but there may well
be other implications of the race which haven't yet been exposed.  I think
it's safer to simply return -ENOENT in this race window, and avoid other
potential problems.  Anything wrong with this?

Thanks for the comments suggesting this approach in the prior thread.

Thanks,

-Eric

---

Return -ENOENT from ext[34]_link if we've raced with unlink and
i_nlink is 0.  Doing otherwise has the potential to corrupt the
orphan inode list, because we'd wind up with an inode with a
non-zero link count on the list, and it will never get properly
cleaned up & removed from the orphan list before it is freed.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Index: linux-2.6.19/fs/ext3/namei.c
===================================================================
--- linux-2.6.19.orig/fs/ext3/namei.c
+++ linux-2.6.19/fs/ext3/namei.c
@@ -2191,6 +2191,8 @@ static int ext3_link (struct dentry * ol
 
 	if (inode->i_nlink >= EXT3_LINK_MAX)
 		return -EMLINK;
+	if (inode->i_nlink == 0)
+		return -ENOENT;
 
 retry:
 	handle = ext3_journal_start(dir, EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
Index: linux-2.6.19/fs/ext4/namei.c
===================================================================
--- linux-2.6.19.orig/fs/ext4/namei.c
+++ linux-2.6.19/fs/ext4/namei.c
@@ -2189,6 +2189,8 @@ static int ext4_link (struct dentry * ol
 
 	if (inode->i_nlink >= EXT4_LINK_MAX)
 		return -EMLINK;
+	if (inode->i_nlink == 0)
+		return -ENOENT;
 
 retry:
 	handle = ext4_journal_start(dir, EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +

Re: [PATCH] return ENOENT from ext3_link when racing with unlink

[Peter Staubach]

Eric Sandeen wrote:
> An update from the earlier thread, [PATCH] [RFC] remove ext3 inode 
> from orphan list when link and unlink race
>
> I think this is better than the original idea of trying to handle the 
> race;
> I've seen that the orphan inode list can get corrupted, but there may 
> well
> be other implications of the race which haven't yet been exposed.  I 
> think
> it's safer to simply return -ENOENT in this race window, and avoid other
> potential problems.  Anything wrong with this?
>
> Thanks for the comments suggesting this approach in the prior thread.
>
> Thanks,
>
> -Eric
>
> ---
>
> Return -ENOENT from ext[34]_link if we've raced with unlink and
> i_nlink is 0.  Doing otherwise has the potential to corrupt the
> orphan inode list, because we'd wind up with an inode with a
> non-zero link count on the list, and it will never get properly
> cleaned up & removed from the orphan list before it is freed.
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>
> Index: linux-2.6.19/fs/ext3/namei.c
> ===================================================================
> --- linux-2.6.19.orig/fs/ext3/namei.c
> +++ linux-2.6.19/fs/ext3/namei.c
> @@ -2191,6 +2191,8 @@ static int ext3_link (struct dentry * ol
>
>     if (inode->i_nlink >= EXT3_LINK_MAX)
>         return -EMLINK;
> +    if (inode->i_nlink == 0)
> +        return -ENOENT;
>
> retry:
>     handle = ext3_journal_start(dir, EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
> Index: linux-2.6.19/fs/ext4/namei.c
> ===================================================================
> --- linux-2.6.19.orig/fs/ext4/namei.c
> +++ linux-2.6.19/fs/ext4/namei.c
> @@ -2189,6 +2189,8 @@ static int ext4_link (struct dentry * ol
>
>     if (inode->i_nlink >= EXT4_LINK_MAX)
>         return -EMLINK;
> +    if (inode->i_nlink == 0)
> +        return -ENOENT;
>
> retry:
>     handle = ext4_journal_start(dir, EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
>

Just out of curosity, what keeps i_nlink from going to 0 immediately
after the new test is executed?

    Thanx...

       ps

Re: [PATCH] return ENOENT from ext3_link when racing with unlink

[Alex Tomas]

>>>>> Peter Staubach (PS) writes:


 PS> Just out of curosity, what keeps i_nlink from going to 0 immediately
 PS> after the new test is executed?

i_mutex in vfs_link() and vfs_unlink()

thanks, Alex

Re: [PATCH] return ENOENT from ext3_link when racing with unlink

[Peter Staubach]

Alex Tomas wrote:
>>>>>> Peter Staubach (PS) writes:
>>>>>>             
>
>
>  PS> Just out of curosity, what keeps i_nlink from going to 0 immediately
>  PS> after the new test is executed?
>
> i_mutex in vfs_link() and vfs_unlink()
>   

Ahhh...  Okie doke, thanx!

       ps