btrfs: propagate error to btrfs_cmp_data_prepare caller

btrfs_cmp_data_prepare() (almost) always returns 0 i.e. ignoring errors
from gather_extent_pages(). While the pages are freed by
btrfs_cmp_data_free(), cmp->num_pages still has > 0. Then,
btrfs_extent_same() try to access the already freed pages causing faults
(or violates PageLocked assertion).

This patch just return the error as is so that the caller stop the process.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Fixes: f441460202cb ("btrfs: fix deadlock with extent-same and readpage")
Cc: <stable@vger.kernel.org> # 4.2
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d4a77993e52f..802df5755cd3 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3028,7 +3028,7 @@ static int btrfs_cmp_data_prepare(struct inode *src, u64 loff,
 out:
         if (ret)
                 btrfs_cmp_data_free(cmp);
-        return 0;
+        return ret;
 }
 
 static int btrfs_cmp_data(u64 len, struct cmp_pages *cmp)