[RFC 6/7] rtmutex: don't check for active hrtimer after adding it

From: Viresh Kumar
Date: Wed Jul 09 2014 - 02:56:39 EST

hrtimer_start*() family never fails to enqueue a hrtimer to a clock-base. The
only special case is when the hrtimer was in past. If it is getting enqueued to
local CPUs's clock-base, we raise a softirq and exit, else we handle that on
next interrupt on remote CPU.

At several places in the kernel, we try to make sure if hrtimer was added
properly or not by calling hrtimer_active(), like:

hrtimer_start(timer, expires, mode);
if (hrtimer_active(timer)) {
/* Added successfully */
} else {
/* Was added in the past */

As hrtimer_start*() never fails, hrtimer_active() is guaranteed to return '1'.
So, there is no point calling hrtimer_active().

This patch updates rtmutex core to get this fixed.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
kernel/locking/rtmutex.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index fc60594..9ea8830 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -922,11 +922,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,

/* Setup the timer, when timeout != NULL */
- if (unlikely(timeout)) {
+ if (unlikely(timeout))
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
- if (!hrtimer_active(&timeout->timer))
- timeout->task = NULL;
- }

ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);


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