On Mon, 2 Jan 2017 20:41:14 +0100
Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
> If we happen to receive interrupts during hv_set_host_time() execution
> our adjustments may get inaccurate. Make the whole function atomic.
> Unfortunately, we can's call do_settimeofday64() with interrupts
> disabled as some cross-CPU work is being done but this call happens
> very rarely.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> drivers/hv/hv_util.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index 4c0fbb0..233d5cb 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -186,6 +186,9 @@ static void hv_set_host_time(struct work_struct *work)
> u64 newtime;
> struct timespec64 host_ts, our_ts;
> struct timex txc = {0};
> + unsigned long flags;
> +
> + local_irq_save(flags);
>
> wrk = container_of(work, struct adj_time_work, work);
>
> @@ -214,6 +217,7 @@ static void hv_set_host_time(struct work_struct *work)
>
> /* Try adjusting time by using phase adjustment if possible */
> if (abs(delta) > MAXPHASE) {
> + local_irq_restore(flags);
> do_settimeofday64(&host_ts);
> return;
> }
> @@ -225,6 +229,8 @@ static void hv_set_host_time(struct work_struct *work)
> txc.status = STA_PLL;
> txc.offset = delta;
> do_adjtimex(&txc);
> +
> + local_irq_restore(flags);
Yes, it should be atomic, but local irq save/restore is not sufficient protection
because it does not protect against premptible kernel. Why not a mutex? or a spinlock?
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