linux-kernel - [PATCH] timers: Clear must_forward

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Date:   Thu, 26 Jul 2018 14:12:02 +0530
From:   Gaurav Kohli <gkohli@...eaurora.org>
To:     john.stultz@...aro.org, tglx@...utronix.de, sboyd@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Gaurav Kohli <gkohli@...eaurora.org>
Subject: [PATCH] timers: Clear must_forward_clk inside base lock

While migrating timer to new base, there is a need
to update base clk by calling forward_timer_base to
avoid stale clock , but at the same time if run_timer
is exectuing in new core it may set must_forward_clk
to false and due to this forward base logic may fail as
per below check:

if (likely(!base->must_forward_clk))
                return;

So preventing the same by putting must_forward_clk inside
base lock.

Signed-off-by: Gaurav Kohli <gkohli@...eaurora.org>

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index cc2d23e..675241d 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1657,6 +1657,19 @@ static inline void __run_timers(struct timer_base *base)
 
 	raw_spin_lock_irq(&base->lock);
 
+	/*
+	 * must_forward_clk must be cleared before running timers so that any
+	 * timer functions that call mod_timer will not try to forward the
+	 * base. idle trcking / clock forwarding logic is only used with
+	 * BASE_STD timers.
+	 *
+	 * The deferrable base does not do idle tracking at all, so we do
+	 * not forward it. This can result in very large variations in
+	 * granularity for deferrable timers, but they can be deferred for
+	 * long periods due to idle.
+	 */
+	base->must_forward_clk = false;
+
 	while (time_after_eq(jiffies, base->clk)) {
 
 		levels = collect_expired_timers(base, heads);
@@ -1676,19 +1689,6 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
-	/*
-	 * must_forward_clk must be cleared before running timers so that any
-	 * timer functions that call mod_timer will not try to forward the
-	 * base. idle trcking / clock forwarding logic is only used with
-	 * BASE_STD timers.
-	 *
-	 * The deferrable base does not do idle tracking at all, so we do
-	 * not forward it. This can result in very large variations in
-	 * granularity for deferrable timers, but they can be deferred for
-	 * long periods due to idle.
-	 */
-	base->must_forward_clk = false;
-
 	__run_timers(base);
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
 		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
-- 
1.9.1