From: Filipe Manana <fdmanana@suse.com>
Date: Wed, 2 Jul 2014 19:07:54 +0000 (+0100)
Subject: Btrfs: read lock extent buffer while walking backrefs
X-Git-Tag: v3.17-rc1~5^2~6
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=6f7ff6d7832c6be13e8c95598884dbc40ad69fb7;p=karo-tx-linux.git

Btrfs: read lock extent buffer while walking backrefs

Before processing the extent buffer, acquire a read lock on it, so
that we're safe against concurrent updates on the extent buffer.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
---

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index e25564bfcb46..a1efd39ca28a 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1001,8 +1001,11 @@ again:
 					ret = -EIO;
 					goto out;
 				}
+				btrfs_tree_read_lock(eb);
+				btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
 				ret = find_extent_in_eb(eb, bytenr,
 							*extent_item_pos, &eie);
+				btrfs_tree_read_unlock_blocking(eb);
 				free_extent_buffer(eb);
 				if (ret < 0)
 					goto out;