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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     David Engraf <david.engraf@sysgo.com>,
        John Stultz <john.stultz@linaro.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.4 027/115] timers, sched_clock: Update timeout
 for clock wrap
Thread-Topic: [PATCH AUTOSEL for 4.4 027/115] timers, sched_clock: Update
 timeout for clock wrap
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Date:   Sat, 3 Mar 2018 22:31:04 +0000
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From: David Engraf <david.engraf@sysgo.com>

[ Upstream commit 1b8955bc5ac575009835e371ae55e7f3af2197a9 ]

The scheduler clock framework may not use the correct timeout for the clock
wrap. This happens when a new clock driver calls sched_clock_register()
after the kernel called sched_clock_postinit(). In this case the clock wrap
timeout is too long thus sched_clock_poll() is called too late and the cloc=
k
already wrapped.

On my ARM system the scheduler was no longer scheduling any other task than
the idle task because the sched_clock() wrapped.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 kernel/time/sched_clock.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index a26036d37a38..382b159d8592 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -205,6 +205,11 @@ sched_clock_register(u64 (*read)(void), int bits, unsi=
gned long rate)
=20
 	update_clock_read_data(&rd);
=20
+	if (sched_clock_timer.function !=3D NULL) {
+		/* update timeout for clock wrap */
+		hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
+	}
+
 	r =3D rate;
 	if (r >=3D 4000000) {
 		r /=3D 1000000;
--=20
2.14.1