linux-kernel - [PATCH 2/2] powerpc/watchdog: ensure watchdog data accesses are protected

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Date:   Tue, 26 Oct 2021 18:27:40 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org
Cc:     npiggin@...il.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] powerpc/watchdog: ensure watchdog data accesses are protected

The wd_smp_cpus_pending CPU mask should be accessed under the protection of
the __wd_smp_lock.

This prevents false alarm to be raised when the system is under an heavy
stress. This has been seen while doing LPM on large system with a big
workload.

Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
---
 arch/powerpc/kernel/watchdog.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index bc7411327066..8d7a1a86187e 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -203,12 +203,13 @@ static void watchdog_smp_panic(int cpu, u64 tb)
 
 static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
 {
+	unsigned long flags;
+
+	wd_smp_lock(&flags);
 	if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) {
 		if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) {
 			struct pt_regs *regs = get_irq_regs();
-			unsigned long flags;
 
-			wd_smp_lock(&flags);
 			cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
 			wd_smp_unlock(&flags);
 
@@ -219,22 +220,23 @@ static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
 				show_regs(regs);
 			else
 				dump_stack();
+			return;
 		}
+
+		wd_smp_unlock(&flags);
 		return;
 	}
+
 	cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
 	if (cpumask_empty(&wd_smp_cpus_pending)) {
-		unsigned long flags;
-
-		wd_smp_lock(&flags);
 		if (cpumask_empty(&wd_smp_cpus_pending)) {
 			wd_smp_last_reset_tb = tb;
 			cpumask_andnot(&wd_smp_cpus_pending,
 					&wd_cpus_enabled,
 					&wd_smp_cpus_stuck);
 		}
-		wd_smp_unlock(&flags);
 	}
+	wd_smp_unlock(&flags);
 }
 
 static void watchdog_timer_interrupt(int cpu)
-- 
2.33.1