+ fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch added to mm-nonmm-unstable branch

+ fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: fs/ext4: use try_cmpxchg in ext4_update_bh_state
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Uros Bizjak <ubizjak@gmail.com>
Subject: fs/ext4: use try_cmpxchg in ext4_update_bh_state
Date: Wed, 2 Nov 2022 08:11:47 +0100

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>
---

 fs/ext4/inode.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/fs/ext4/inode.c~fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state
+++ a/fs/ext4/inode.c
@@ -786,11 +786,10 @@ static void ext4_update_bh_state(struct
 	 * 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,
_

Patches currently in -mm which might be from ubizjak@gmail.com are

lib-genalloc-use-try_cmpxchg-in-setclear_bits_ll.patch
fs-ext4-use-try_cmpxchg-in-ext4_update_bh_state.patch