[PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[Josef Bacik]

You can run into this problem where if somebody is fsyncing and writing out
the existing extents you will have removed the extent map from the em tree,
but it's still valid for the current fsync so we go ahead and write it.  The
problem is we unconditionally try to merge it back into the em tree, but if
we've removed it from the em tree that will cause problems.  So fix this by
only trying to merge it in if it is still a part of the tree.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
---
 fs/btrfs/extent_map.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index ed88f5e..9759911 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -289,7 +289,8 @@ out:
 void clear_em_logging(struct extent_map_tree *tree, struct extent_map *em)
 {
 	clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
-	try_merge_map(tree, em);
+	if (em->in_tree)
+		try_merge_map(tree, em);
 }
 
 /**
-- 
1.7.7.6

Re: [PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[Zach Brown]

> problem is we unconditionally try to merge it back into the em tree, but if
> we've removed it from the em tree that will cause problems.  So fix this by

What problems?  If I were staring at the symptoms of this bug how would
I find that this commit fixes it?

- z

Re: [PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[Josef Bacik]

On Mon, Jan 28, 2013 at 11:52:26AM -0700, Zach Brown wrote:
> > problem is we unconditionally try to merge it back into the em tree, but if
> > we've removed it from the em tree that will cause problems.  So fix this by
> 
> What problems?  If I were staring at the symptoms of this bug how would
> I find that this commit fixes it?
> 

I'll fix the commit message, we just add something to the tree that doesn't have
a ref so it's a basic use after free sort of scenario. Thanks,

Josef
> - z

Re: [PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[Zach Brown]

> I'll fix the commit message, we just add something to the tree that doesn't have
> a ref so it's a basic use after free sort of scenario. Thanks,

Thanks, complete commit messages help us old farts keep up.

- z

Re: [PATCH] Btrfs: do not merge logged extents if we've removed them from the tree

[Liu Bo]

On Mon, Jan 28, 2013 at 09:52:56AM -0500, Josef Bacik wrote:
> You can run into this problem where if somebody is fsyncing and writing out
> the existing extents you will have removed the extent map from the em tree,
> but it's still valid for the current fsync so we go ahead and write it.  The
> problem is we unconditionally try to merge it back into the em tree, but if
> we've removed it from the em tree that will cause problems.  So fix this by
> only trying to merge it in if it is still a part of the tree.  Thanks,
> 

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
> ---
>  fs/btrfs/extent_map.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
> index ed88f5e..9759911 100644
> --- a/fs/btrfs/extent_map.c
> +++ b/fs/btrfs/extent_map.c
> @@ -289,7 +289,8 @@ out:
>  void clear_em_logging(struct extent_map_tree *tree, struct extent_map *em)
>  {
>  	clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
> -	try_merge_map(tree, em);
> +	if (em->in_tree)
> +		try_merge_map(tree, em);
>  }
>  
>  /**
> -- 
> 1.7.7.6
> 
> --
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