linux-kernel - [PATCH] tick: use READ_ONCE() to read jiffies in concurrent environment

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Date: Sun, 25 Feb 2024 11:12:50 +0800
From: linke li <lilinke99@...com>
To: 
Cc: lilinke99@...com,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] tick: use READ_ONCE() to read jiffies in concurrent environment

In function tick_sched_do_timer(), jiffies is read using READ_ONCE()
in line 224, while read directly in line 217

217	if (ts->last_tick_jiffies != jiffies) {
218		ts->stalled_jiffies = 0;
219		ts->last_tick_jiffies = READ_ONCE(jiffies);
220	} else {
221		if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
222			tick_do_update_jiffies64(now);
223			ts->stalled_jiffies = 0;
224			ts->last_tick_jiffies = READ_ONCE(jiffies);
225		}
226	}

There is patch similar to this. commit c1c0ce31b242 ("r8169: fix the KCSAN reported data-race in rtl_tx() while reading tp->cur_tx")
This patch find two read of same variable while one is protected, another
is not. And READ_ONCE() is added to protect.

Signed-off-by: linke li <lilinke99@...com>
---
 kernel/time/tick-sched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 01fb50c1b17e..aa684511c25a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -214,7 +214,7 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
 	 * If the jiffies update stalled for too long (timekeeper in stop_machine()
 	 * or VMEXIT'ed for several msecs), force an update.
 	 */
-	if (ts->last_tick_jiffies != jiffies) {
+	if (ts->last_tick_jiffies != READ_ONCE(jiffies)) {
 		ts->stalled_jiffies = 0;
 		ts->last_tick_jiffies = READ_ONCE(jiffies);
 	} else {
-- 
2.39.3 (Apple Git-145)