Re: [PATCH v3] Btrfs: fix eb memory leak due to readpage failure

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Jul 11, 2016 at 02:27:39PM -0400, Chris Mason wrote:
> 
> 
> On 07/11/2016 01:39 PM, Liu Bo wrote:
> > eb->io_pages is set in read_extent_buffer_pages().
> > 
> > In case of readpage failure, for pages that have been added to bio,
> > it calls bio_endio and later readpage_io_failed_hook() does the work.
> > 
> > When this eb's page (couldn't be the 1st page) fails to add itself to bio
> > due to failure in merge_bio(), it cannot decrease eb->io_pages via bio_endio,
> >  and ends up with a memory leak eventually.
> > 
> > This lets __do_readpage propagate errors to callers and adds the
> >  'atomic_dec(&eb->io_pages)'.
> 
> Thanks for looking at this Liu, how is it currently being tested?

I have a btrfs disk image which was corrupted by btrfs-corrupt-block
tool, in that image, the chunk tree's content has been removed while the
chunk node can be read from read successfully, so we'd get -EIO when
trying to read tree root's node since __btrfs_map_block() would fail to
find the right item in chunk mapping_tree.  Thus, we can test our error
handling path in read_extent_buffer_pages().

Thanks,

-liubo

> 
> -chris