linux-kernel - [PATCH] workqueue: update wq_watchdog_touched for unbound lockup checking

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Date:   Fri, 19 Mar 2021 15:24:48 +0800
From:   Wang Qing <wangqing@...o.com>
To:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Wang Qing <wangqing@...o.com>
Subject: [PATCH] workqueue: update wq_watchdog_touched for unbound lockup checking

When touch_softlockup_watchdog() is called, only wq_watchdog_touched_cpu 
updated, while the unbound worker_pool running on its core uses 
wq_watchdog_touched to determine whether locked up. This may be mischecked.

My suggestion is to update both when touch_softlockup_watchdog() is called, 
use wq_watchdog_touched_cpu to check bound, and use wq_watchdog_touched 
to check unbound worker_pool.

Signed-off-by: Wang Qing <wangqing@...o.com>
---
 kernel/workqueue.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0d150da..be08295
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5787,22 +5787,17 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
 			continue;
 
 		/* get the latest of pool and touched timestamps */
+		if (pool->cpu >= 0)
+			touched = READ_ONCE(per_cpu(wq_watchdog_touched_cpu, pool->cpu));
+		else
+			touched = READ_ONCE(wq_watchdog_touched);
 		pool_ts = READ_ONCE(pool->watchdog_ts);
-		touched = READ_ONCE(wq_watchdog_touched);
 
 		if (time_after(pool_ts, touched))
 			ts = pool_ts;
 		else
 			ts = touched;
 
-		if (pool->cpu >= 0) {
-			unsigned long cpu_touched =
-				READ_ONCE(per_cpu(wq_watchdog_touched_cpu,
-						  pool->cpu));
-			if (time_after(cpu_touched, ts))
-				ts = cpu_touched;
-		}
-
 		/* did we stall? */
 		if (time_after(jiffies, ts + thresh)) {
 			lockup_detected = true;
@@ -5826,8 +5821,8 @@ notrace void wq_watchdog_touch(int cpu)
 {
 	if (cpu >= 0)
 		per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies;
-	else
-		wq_watchdog_touched = jiffies;
+
+	wq_watchdog_touched = jiffies;
 }
 
 static void wq_watchdog_set_thresh(unsigned long thresh)
-- 
2.7.4