timers: Use deferrable base independent of base::nohz_active

During boot and before base::nohz_active is set in the timer bases, deferrable
timers are enqueued into the standard timer base. This works correctly as
long as base::nohz_active is false.

Once it base::nohz_active is set and a timer which was enqueued before that
is accessed the lock selector code choses the lock of the deferred
base. This causes unlocked access to the standard base and in case the
timer is removed it does not clear the pending flag in the standard base
bitmap which causes get_next_timer_interrupt() to return bogus values.

To prevent that, the deferrable timers must be enqueued in the deferrable
base, even when base::nohz_active is not set. Those deferrable timers also
need to be expired unconditional.

Fixes: 500462a ("timers: Switch to a non-cascading wheel")
Signed-off-by: Anna-Maria Gleixner <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sebastian Siewior <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Paul McKenney <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

kernel/time/timer.c

@@ -823,11 +823,10 @@ static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
 	struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_STD], cpu);
 
 	/*
-	 * If the timer is deferrable and nohz is active then we need to use
-	 * the deferrable base.
+	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
+	 * to use the deferrable base.
 	 */
-	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active &&
-	    (tflags & TIMER_DEFERRABLE))
+	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
 		base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
 	return base;
 }
@@ -837,11 +836,10 @@ static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
 	/*
-	 * If the timer is deferrable and nohz is active then we need to use
-	 * the deferrable base.
+	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
+	 * to use the deferrable base.
 	 */
-	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active &&
-	    (tflags & TIMER_DEFERRABLE))
+	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
 		base = this_cpu_ptr(&timer_bases[BASE_DEF]);
 	return base;
 }
@@ -1684,7 +1682,7 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 	base->must_forward_clk = false;
 
 	__run_timers(base);
-	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && base->nohz_active)
+	if (IS_ENABLED(CONFIG_NO_HZ_COMMON))
 		__run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]));
 }