[PATCH] hrtimer: Refresh softirq deadline after clock changes in low-res mode

[Avi Weiss <thnkslprpt@gmail.com>]

In periodic low-resolution mode, hrtimer_run_queues() updates the clock
base offsets at each tick but does not refresh softirq_expires_next.
When CLOCK_REALTIME is moved forward, an expired soft hrtimer can
therefore remain pending until the old monotonic deadline is reached.

Reevaluate the next expiry when hrtimer_update_base() observes a new
clock-was-set sequence, before checking whether to raise HRTIMER_SOFTIRQ.

Fixes: 5da70160462e ("hrtimer: Implement support for softirq based hrtimers")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
 kernel/time/hrtimer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 17dd38a6cee7..5d1df371e931 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2289,6 +2289,7 @@ void hrtimer_run_queues(void)
 	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
 	unsigned long flags;
 	ktime_t now;
+	unsigned int seq;
 
 	if (hrtimer_hres_active(cpu_base))
 		return;
@@ -2306,7 +2307,10 @@ void hrtimer_run_queues(void)
 	}
 
 	raw_spin_lock_irqsave(&cpu_base->lock, flags);
+	seq = cpu_base->clock_was_set_seq;
 	now = hrtimer_update_base(cpu_base);
+	if (seq != cpu_base->clock_was_set_seq)
+		hrtimer_update_next_event(cpu_base);
 
 	if (!ktime_before(now, cpu_base->softirq_expires_next)) {
 		cpu_base->softirq_expires_next = KTIME_MAX;

base-commit: cbbddb6b08cc9900a87cccaa9b22bbe06aa4f50a
-- 
2.53.0