This is a note to let you know that I've just added the patch titled
timers/tick/broadcast-hrtimer: Fix suspicious RCU usage in idle loop
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timers-tick-broadcast-hrtimer-fix-suspicious-rcu-usage-in-idle-loop.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a127d2bcf1fbc8c8e0b5cf0dab54f7d3ff50ce47 Mon Sep 17 00:00:00 2001
From: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
Date: Wed, 18 Mar 2015 16:19:27 +0530
Subject: timers/tick/broadcast-hrtimer: Fix suspicious RCU usage in idle loop
From: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
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().
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-broadcast-hrtimer.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- 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
*/
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,
* 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()) {
Patches currently in stable-queue which might be from preeti@xxxxxxxxxxxxxxxxxx are
queue-3.19/powerpc-fix-memory-corruption-by-pnv_alloc_idle_core_states.patch
queue-3.19/timers-tick-broadcast-hrtimer-fix-suspicious-rcu-usage-in-idle-loop.patch
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