Re: [PATCH] Btrfs: deal with existing encompassing extent map in btrfs_get_extent()

["Holger Hoffstätte" <holger@applied-asynchrony.com>]

On 11/10/16 16:06, David Sterba wrote:
> On Wed, Nov 09, 2016 at 03:26:50PM -0800, Omar Sandoval wrote:
>> From: Omar Sandoval <osandov@fb.com>
>> [snip]
>> Commit 8dff9c853410 ("Btrfs: deal with duplciates during extent_map
>> insertion in btrfs_get_extent") fixed a case in btrfs_get_extent() where
>> two threads race on adding the same extent map to an inode's extent map
>> tree. However, if the added em is merged with an adjacent em in the
>> extent tree, then we'll end up with an existing extent that is not
>> identical to but instead encompasses the extent we tried to add. When we
>> call merge_extent_mapping() to find the nonoverlapping part of the new
>> em, the arithmetic overflows because there is no such thing. We then end
>> up trying to add a bogus em to the em_tree, which results in a EEXIST
>> that can bubble all the way up to userspace.
> 
> Is this possibly the same bug that Liu Bo fixes in
> https://patchwork.kernel.org/patch/9413129/ ?

Seem similar, but I can't reproduce without that patch either..

-h