linux-kernel - [PATCH] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240919081432.23431-1-ubizjak@gmail.com>
Date: Thu, 19 Sep 2024 10:14:05 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Chandan Babu R <chandan.babu@...cle.com>,
	"Darrick J. Wong" <djwong@...nel.org>
Subject: [PATCH] xfs: Use try_cmpxchg() in xlog_cil_insert_pcp_aggregate()

Use !try_cmpxchg instead of cmpxchg (*ptr, old, new) != old in
xlog_cil_insert_pcp_aggregate().  x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after 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.

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@...il.com>
Cc: Chandan Babu R <chandan.babu@...cle.com>
Cc: "Darrick J. Wong" <djwong@...nel.org>
---
 fs/xfs/xfs_log_cil.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 391a938d690c..e7a9fcd6935b 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -171,13 +171,12 @@ xlog_cil_insert_pcp_aggregate(
 	 * structures that could have a nonzero space_used.
 	 */
 	for_each_cpu(cpu, &ctx->cil_pcpmask) {
-		int	old, prev;
+		int	old;
 
 		cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+		old = READ_ONCE(cilpcp->space_used);
 		do {
-			old = cilpcp->space_used;
-			prev = cmpxchg(&cilpcp->space_used, old, 0);
-		} while (old != prev);
+		} while (!try_cmpxchg(&cilpcp->space_used, &old, 0));
 		count += old;
 	}
 	atomic_add(count, &ctx->space_used);
-- 
2.46.1