Patch "perf/x86/amd: Use try_cmpxchg() in events/amd/{un,}core.c" has been added to the 6.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    perf/x86/amd: Use try_cmpxchg() in events/amd/{un,}core.c

to the 6.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-x86-amd-use-try_cmpxchg-in-events-amd-un-core.c.patch
and it can be found in the queue-6.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7aea1d980841c78c46186af0ade988b6db7de3ee
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
Date:   Thu Apr 25 12:16:14 2024 +0200

    perf/x86/amd: Use try_cmpxchg() in events/amd/{un,}core.c
    
    [ Upstream commit cd84351c8c1baec86342d784feb884ace007d51c ]
    
    Replace this pattern in events/amd/{un,}core.c:
    
        cmpxchg(*ptr, old, new) == old
    
    ... with the simpler and faster:
    
        try_cmpxchg(*ptr, &old, new)
    
    The x86 CMPXCHG instruction returns success in the ZF flag, so this change
    saves a compare after the CMPXCHG.
    
    No functional change intended.
    
    Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
    Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240425101708.5025-1-ubizjak@xxxxxxxxx
    Stable-dep-of: f73cefa3b72e ("perf/x86: Fix smp_processor_id()-in-preemptible warnings")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 1fc4ce44e743c..18bfe3451f3aa 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -433,7 +433,9 @@ static void __amd_put_nb_event_constraints(struct cpu_hw_events *cpuc,
 	 * when we come here
 	 */
 	for (i = 0; i < x86_pmu.num_counters; i++) {
-		if (cmpxchg(nb->owners + i, event, NULL) == event)
+		struct perf_event *tmp = event;
+
+		if (try_cmpxchg(nb->owners + i, &tmp, NULL))
 			break;
 	}
 }
diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 5a4bfe9aea237..0bfde2ea5cb8c 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -162,7 +162,9 @@ static int amd_uncore_add(struct perf_event *event, int flags)
 	/* if not, take the first available counter */
 	hwc->idx = -1;
 	for (i = 0; i < pmu->num_counters; i++) {
-		if (cmpxchg(&ctx->events[i], NULL, event) == NULL) {
+		struct perf_event *tmp = NULL;
+
+		if (try_cmpxchg(&ctx->events[i], &tmp, event)) {
 			hwc->idx = i;
 			break;
 		}
@@ -196,7 +198,9 @@ static void amd_uncore_del(struct perf_event *event, int flags)
 	event->pmu->stop(event, PERF_EF_UPDATE);
 
 	for (i = 0; i < pmu->num_counters; i++) {
-		if (cmpxchg(&ctx->events[i], event, NULL) == event)
+		struct perf_event *tmp = event;
+
+		if (try_cmpxchg(&ctx->events[i], &tmp, NULL))
 			break;
 	}