[PATCH V1 Resend] hrtimer: call switch_hrtimer_base() after setting new expiry time

[Viresh Kumar]

In switch_hrtimer_base() we are calling hrtimer_check_target() which guarantees
this:

/*
 * With HIGHRES=y we do not migrate the timer when it is expiring
 * before the next event on the target cpu because we cannot reprogram
 * the target cpu hardware and we would cause it to fire late.
 *
 * Called with cpu_base->lock of target cpu held.
 */

But switch_hrtimer_base() is only called from one place, i.e.
__hrtimer_start_range_ns() and at that point (where we call
switch_hrtimer_base()) expiration time is not yet known as we call this routine
later: hrtimer_set_expires_range_ns().

To fix this, we need to find the updated expiry time before calling
switch_hrtimer_base().

Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
Hi Thomas,

I have sent this previously as part of: https://lkml.org/lkml/2014/4/4/23

But as you asked to send bugfixes without any dependencies for ticks patches, I
thought of sending bugfixes separately for timers too. This was the only bugfix
from that series and other patches don't conflict with it, so I am not resending
other patches from above series again.

Not adding any stable tags as this is broken from a long long time and don't
know if you want to fix it for those kernels.

 kernel/hrtimer.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index d55092c..c86b95a 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -968,11 +968,8 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	/* Remove an active timer from the queue: */
 	ret = remove_hrtimer(timer, base);
 
-	/* Switch the timer base, if necessary: */
-	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
-
 	if (mode & HRTIMER_MODE_REL) {
-		tim = ktime_add_safe(tim, new_base->get_time());
+		tim = ktime_add_safe(tim, base->get_time());
 		/*
 		 * CONFIG_TIME_LOW_RES is a temporary way for architectures
 		 * to signal that they simply return xtime in
@@ -987,6 +984,9 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 
 	hrtimer_set_expires_range_ns(timer, tim, delta_ns);
 
+	/* Switch the timer base, if necessary: */
+	new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
+
 	timer_stats_hrtimer_set_start_info(timer);
 
 	leftmost = enqueue_hrtimer(timer, new_base);
-- 
1.7.12.rc2.18.g61b472e

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