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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: Uros Bizjak <ubizjak@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2022-11-02 08:11:47 +01:00 committed by Andrew Morton
parent 74b7046d32
commit 3ee2a3e7c1
1 changed files with 2 additions and 3 deletions
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5
fs/ext4/inode.c
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@ -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.
*/
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,