Commit 3ee2a3e7 authored by Uros Bizjak's avatar Uros Bizjak Committed by Andrew Morton
Browse files

fs/ext4: use try_cmpxchg in ext4_update_bh_state 

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.

Link: https://lkml.kernel.org/r/20221102071147.6642-1-ubizjak@gmail.com


Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 74b7046d

fs/ext4/inode.c

+2 −3
Original line number Diff line number Diff line
@@ -786,11 +786,10 @@ 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.

	 */

	do {

	old_state = READ_ONCE(bh->b_state);

	do {

		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,