Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
ext4_update_bh_state. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.
No functional change intended.
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
---
fs/ext4/inode.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 2b5ef1b64249..162e39e2f59a 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -780,11 +780,10 @@ static void ext4_update_bh_state(struct buffer_head *bh, unsigned long flags)
* once we get rid of using bh as a container for mapping information
* to pass to / from get_block functions, this can go away.
*/
+ old_state = READ_ONCE(bh->b_state);
do {
- old_state = READ_ONCE(bh->b_state);
new_state = (old_state & ~EXT4_MAP_FLAGS) | flags;
- } while (unlikely(
- cmpxchg(&bh->b_state, old_state, new_state) != old_state));
+ } while (unlikely(!try_cmpxchg(&bh->b_state, &old_state, new_state)));
}
static int _ext4_get_block(struct inode *inode, sector_t iblock,
--
2.37.3
