linux-kernel - [PATCH V2 1/2] hrtimer: update '->active_bases' before calling hrtimer_force

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Date:	Tue,  7 Apr 2015 07:40:52 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH V2 1/2] hrtimer: update '->active_bases' before calling hrtimer_force_reprogram()

'active_bases' indicates which clock-base have active timers. While it
is updated correctly, it is hardly used. Next commit will start using it
to make code more efficient, but before that we need to fix a problem.

While removing hrtimers, in __remove_hrtimer():
- We first remove the hrtimer from the queue.
- Then reprogram clockevent device if required
  (hrtimer_force_reprogram()).
- And then finally clear 'active_bases', if no more timers are pending
  on the current clock base (from which we are removing the hrtimer).

hrtimer_force_reprogram() needs to loop over all active clock bases to
find the next expiry event, and while doing so it will use
'active_bases' (after next commit). And it will find the current base
active, as we haven't cleared it until now, even if current clock base
has no more hrtimers queued.

The next commit will skip validating what timerqueue_getnext() returns,
as that is guaranteed to be valid for an active base, and the above
stated problem will result in a crash then (Because timerqueue_getnext()
will return NULL for the current clock base).

So, fix this issue by clearing active_bases before calling
hrtimer_force_reprogram().

Reviewed-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/time/hrtimer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index bee0c1f78091..3152f327c988 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -879,6 +879,9 @@ static void __remove_hrtimer(struct hrtimer *timer,
 
 	next_timer = timerqueue_getnext(&base->active);
 	timerqueue_del(&base->active, &timer->node);
+	if (!timerqueue_getnext(&base->active))
+		base->cpu_base->active_bases &= ~(1 << base->index);
+
 	if (&timer->node == next_timer) {
 #ifdef CONFIG_HIGH_RES_TIMERS
 		/* Reprogram the clock event device. if enabled */
@@ -892,8 +895,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
 		}
 #endif
 	}
-	if (!timerqueue_getnext(&base->active))
-		base->cpu_base->active_bases &= ~(1 << base->index);
 out:
 	timer->state = newstate;
 }
-- 
2.3.0.rc0.44.ga94655d

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