On Thu, Jul 17, 2014 at 11:44:14AM +0800, Wang Shilong wrote:
> btrfs_next_leaf() will use current leaf's last key to search
> and then return a bigger one. So it may still return a file extent
> item that is smaller than expected value and we will
> get an overflow here for @em->len.
> 
> This is easy to reproduce for Btrfs Direct writting, it did not
> cause any problem, because writting will re-insert right mapping later.
> 
> However, by hacking code to make DIO support compression, wrong extent
> mapping is kept and it encounter merging failure(EEXIST) quickly.

So this cannot happen normally (because compression and DIO do not work
together)?

> Fix this problem by looping to find next file extent item that is bigger
> than @start or we could not find anything more.
> 
> Signed-off-by: Wang Shilong <wangsl.f...@cn.fujitsu.com>

Reviewed-by: David Sterba <dste...@suse.cz>
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