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    Subject[PATCH 2/2] time: Fix change_clocksource locking
    Date
    change_clocksource() fails to grab locks or call timekeeping_update(),
    which leaves a race window for time inconsistencies.

    This adds proper locking and a call to timekeeping_update() to fix this.

    CC: Andy Lutomirski <luto@amacapital.net>
    CC: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: John Stultz <john.stultz@linaro.org>
    ---
    kernel/time/timekeeping.c | 7 +++++++
    1 files changed, 7 insertions(+), 0 deletions(-)

    diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
    index 403c2a0..b53da5e 100644
    --- a/kernel/time/timekeeping.c
    +++ b/kernel/time/timekeeping.c
    @@ -448,9 +448,12 @@ EXPORT_SYMBOL(timekeeping_inject_offset);
    static int change_clocksource(void *data)
    {
    struct clocksource *new, *old;
    + unsigned long flags;

    new = (struct clocksource *) data;

    + write_seqlock_irqsave(&timekeeper.lock, flags);
    +
    timekeeping_forward_now();
    if (!new->enable || new->enable(new) == 0) {
    old = timekeeper.clock;
    @@ -458,6 +461,10 @@ static int change_clocksource(void *data)
    if (old->disable)
    old->disable(old);
    }
    + timekeeping_update(true);
    +
    + write_sequnlock_irqrestore(&timekeeper.lock, flags);
    +
    return 0;
    }

    --
    1.7.3.2.146.gca209


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