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    Subject[PATCH 4.4 027/134] timers, sched_clock: Update timeout for clock wrap
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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 clock
    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    kernel/time/sched_clock.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/kernel/time/sched_clock.c
    +++ b/kernel/time/sched_clock.c
    @@ -205,6 +205,11 @@ sched_clock_register(u64 (*read)(void),

    update_clock_read_data(&rd);

    + if (sched_clock_timer.function != NULL) {
    + /* update timeout for clock wrap */
    + hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
    + }
    +
    r = rate;
    if (r >= 4000000) {
    r /= 1000000;

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