Hi,
Can you please add stable@xxxxxxxxxxxxxxx to the Cc?
Without the patch, we get RCU warnings during bootup.
Hence the patch is important for the stable kernels as well.
Regards
Preeti U Murthy
On 03/23/2015 05:54 PM, tip-bot for Preeti U Murthy wrote:
> Commit-ID: a127d2bcf1fbc8c8e0b5cf0dab54f7d3ff50ce47
> Gitweb: http://git.kernel.org/tip/a127d2bcf1fbc8c8e0b5cf0dab54f7d3ff50ce47
> Author: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
> AuthorDate: Wed, 18 Mar 2015 16:19:27 +0530
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Mon, 23 Mar 2015 10:50:05 +0100
>
> timers/tick/broadcast-hrtimer: Fix suspicious RCU usage in idle loop
>
> The hrtimer mode of broadcast queues hrtimers in the idle entry
> path so as to wakeup cpus in deep idle states. The associated
> call graph is :
>
> cpuidle_idle_call()
> |____ clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, ....))
> |_____tick_broadcast_set_event()
> |____clockevents_program_event()
> |____bc_set_next()
>
> The hrtimer_{start/cancel} functions call into tracing which uses RCU.
> But it is not legal to call into RCU in cpuidle because it is one of the
> quiescent states. Hence protect this region with RCU_NONIDLE which informs
> RCU that the cpu is momentarily non-idle.
>
> As an aside it is helpful to point out that the clock event device that is
> programmed here is not a per-cpu clock device; it is a
> pseudo clock device, used by the broadcast framework alone.
> The per-cpu clock device programming never goes through bc_set_next().
>
> Signed-off-by: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxx
> Cc: mpe@xxxxxxxxxxxxxx
> Cc: tglx@xxxxxxxxxxxxx
> Link: http://lkml.kernel.org/r/20150318104705.17763.56668.stgit@xxxxxxxxxxxxxxxxx
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
> kernel/time/tick-broadcast-hrtimer.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadcast-hrtimer.c
> index eb682d5..6aac4be 100644
> --- a/kernel/time/tick-broadcast-hrtimer.c
> +++ b/kernel/time/tick-broadcast-hrtimer.c
> @@ -49,6 +49,7 @@ static void bc_set_mode(enum clock_event_mode mode,
> */
> static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
> {
> + int bc_moved;
> /*
> * We try to cancel the timer first. If the callback is on
> * flight on some other cpu then we let it handle it. If we
> @@ -60,9 +61,15 @@ static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
> * restart the timer because we are in the callback, but we
> * can set the expiry time and let the callback return
> * HRTIMER_RESTART.
> + *
> + * Since we are in the idle loop at this point and because
> + * hrtimer_{start/cancel} functions call into tracing,
> + * calls to these functions must be bound within RCU_NONIDLE.
> */
> - if (hrtimer_try_to_cancel(&bctimer) >= 0) {
> - hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
> + RCU_NONIDLE(bc_moved = (hrtimer_try_to_cancel(&bctimer) >= 0) ?
> + !hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED) :
> + 0);
> + if (bc_moved) {
> /* Bind the "device" to the cpu */
> bc->bound_on = smp_processor_id();
> } else if (bc->bound_on == smp_processor_id()) {
>
--
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