[PATCH] fix next_timer_interrupt() for hrtimer

Also from Thomas Gleixner <tglx@linutronix.de>

Function next_timer_interrupt() got broken with a recent patch
6ba1b91213e81aa92b5cf7539f7d2a94ff54947c as sys_nanosleep() was moved to
hrtimer.  This broke things as next_timer_interrupt() did not check hrtimer
tree for next event.

Function next_timer_interrupt() is needed with dyntick (CONFIG_NO_IDLE_HZ,
VST) implementations, as the system can be in idle when next hrtimer event
was supposed to happen.  At least ARM and S390 currently use
next_timer_interrupt().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/arm/kernel/time.c b/arch/arm/kernel/time.c
index d7d932c02866..d6bd435a6857 100644
--- a/arch/arm/kernel/time.c
+++ b/arch/arm/kernel/time.c
@@ -422,12 +422,14 @@ static int timer_dyn_tick_disable(void)
 void timer_dyn_reprogram(void)
 {
         struct dyn_tick_timer *dyn_tick = system_timer->dyn_tick;
+        unsigned long next, seq;
 
-        if (dyn_tick) {
-                write_seqlock(&xtime_lock);
-                if (dyn_tick->state & DYN_TICK_ENABLED)
+        if (dyn_tick && (dyn_tick->state & DYN_TICK_ENABLED)) {
+                next = next_timer_interrupt();
+                do {
+                        seq = read_seqbegin(&xtime_lock);
                         dyn_tick->reprogram(next_timer_interrupt() - jiffies);
-                write_sequnlock(&xtime_lock);
+                } while (read_seqretry(&xtime_lock, seq));
         }
 }