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timers/tick/broadcast-hrtimer: Fix suspicious RCU usage in idle loop 

commit a127d2bcf1fbc8c8e0b5cf0dab54f7d3ff50ce47 upstream.

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().

Change-Id: If3ee2d37d773e23a4a145c17fa4e1e1cd31c74cf
Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linuxppc-dev@ozlabs.org
Cc: mpe@ellerman.id.au
Cc: tglx@linutronix.de
Link: http://lkml.kernel.org/r/20150318104705.17763.56668.stgit@preeti.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
This commit is contained in:
Preeti U Murthy 2015-03-18 16:19:27 +05:30 committed by syphyr
parent 4e2f293610
commit 3a77014aa4
1 changed files with 9 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
kernel/time/tick-broadcast-hrtimer.c
View File

@ -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()) {