[GIT PULL] timer fix

[Ingo Molnar]

Linus,

Please pull the latest timers-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
timers-urgent-for-linus

   # HEAD: e430d802d6a3aaf61bd3ed03d9404888a29b9bf9 timer: Read jiffies once 
when forwarding base clk

Fixes a timer expiry bug that would cause spurious delay of timers.

 Thanks,

        Ingo

------------------>
Li RongQing (1):
      timer: Read jiffies once when forwarding base clk


 kernel/time/timer.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 0e315a2e77ae..4820823515e9 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1678,24 +1678,26 @@ void timer_clear_idle(void)
 static int collect_expired_timers(struct timer_base *base,
                                  struct hlist_head *heads)
 {
+       unsigned long now = READ_ONCE(jiffies);
+
        /*
         * NOHZ optimization. After a long idle sleep we need to forward the
         * base to current jiffies. Avoid a loop by searching the bitfield for
         * the next expiring timer.
         */
-       if ((long)(jiffies - base->clk) > 2) {
+       if ((long)(now - base->clk) > 2) {
                unsigned long next = __next_timer_interrupt(base);
 
                /*
                 * If the next timer is ahead of time forward to current
                 * jiffies, otherwise forward to the next expiry time:
                 */
-               if (time_after(next, jiffies)) {
+               if (time_after(next, now)) {
                        /*
                         * The call site will increment base->clk and then
                         * terminate the expiry loop immediately.
                         */
-                       base->clk = jiffies;
+                       base->clk = now;
                        return 0;
                }
                base->clk = next;