archives/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-03-08 03:04:51 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

fs: Use try_cmpxchg() in start_dir_add()

Browse source 
Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) == old.

The x86 CMPXCHG instruction returns success in the ZF flag,
so this change saves a compare after CMPXCHG (and related
move instruction in front of CMPXCHG).

Note that the value from *ptr should be read using READ_ONCE() to
prevent the compiler from merging, refetching or reordering the read.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/20250811125308.616717-1-ubizjak@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Uros Bizjak 2025-08-11 14:52:38 +02:00 • committed by Christian Brauner
parent 278033a225
commit 14498ca7e0
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
1 changed files with 2 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

4
fs/dcache.c
View file

@ -2509,8 +2509,8 @@ static inline unsigned start_dir_add(struct inode *dir)
{
preempt_disable_nested();
for (;;) {
unsigned n = dir->i_dir_seq;
if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
unsigned n = READ_ONCE(dir->i_dir_seq);
if (!(n & 1) && try_cmpxchg(&dir->i_dir_seq, &n, n + 1))
return n;
cpu_relax();
}