[PATCH 3.12 106/118] Btrfs: do a full search everytime in btrfs_search_old_slot

Greg Kroah-Hartman
2013-12-18T21:19:46Z

From: Josef Bacik <jbacik@fusionio.com>

commit d4b4087c43cc00a196c5be57fac41f41309f1d56 upstream.

While running some snashot aware defrag tests I noticed I was panicing every
once and a while in key_search. This is because of the optimization that says
if we find a key at slot 0 it will be at slot 0 all the way down the rest of the
tree. This isn't the case for btrfs_search_old_slot since it will likely replay
changes to a buffer if something has changed since we took our sequence number.
So short circuit this optimization by setting prev_cmp to -1 every time we call
key_search so we will do our normal binary search. With this patch I am no
longer seeing the panics I was seeing before. Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/ctree.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -2758,7 +2758,7 @@ int btrfs_search_old_slot(struct btrfs_r
int level;
int lowest_unlock = 1;
u8 lowest_level = 0;
- int prev_cmp;
+ int prev_cmp = -1;

lowest_level = p->lowest_level;
WARN_ON(p->nodes[0] != NULL);
@@ -2769,7 +2769,6 @@ int btrfs_search_old_slot(struct btrfs_r
}

again:
- prev_cmp = -1;
b = get_old_root(root, time_seq);
level = btrfs_header_level(b);
p->locks[level] = BTRFS_READ_LOCK;
@@ -2787,6 +2786,11 @@ again:
*/
btrfs_unlock_up_safe(p, level + 1);

+ /*
+ * Since we can unwind eb's we want to do a real search every
+ * time.
+ */
+ prev_cmp = -1;
ret = key_search(b, key, level, &prev_cmp, &slot);

if (level != 0) {