posix-timers: Rework cancel retry loops

As a preparatory step for adding the PREEMPT RT specific synchronization
mechanism to wait for a running timer callback, rework the timer cancel
retry loops so they call a common function. This allows trivial
substitution in one place.

Originally-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190730223828.874901027@linutronix.de

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index f5aedd2..bbe8f96 100644 (file)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -805,6 +805,17 @@ static int common_hrtimer_try_to_cancel(struct k_itimer *timr)
        return hrtimer_try_to_cancel(&timr->it.real.timer);
 }
 
+static struct k_itimer *timer_wait_running(struct k_itimer *timer,
+                                          unsigned long *flags)
+{
+       timer_t timer_id = READ_ONCE(timer->it_id);
+
+       unlock_timer(timer, *flags);
+       cpu_relax();
+       /* Relock the timer. It might be not longer hashed. */
+       return lock_timer(timer_id, flags);
+}
+
 /* Set a POSIX.1b interval timer. */
 int common_timer_set(struct k_itimer *timr, int flags,
                     struct itimerspec64 *new_setting,
@@ -859,8 +870,9 @@ static int do_timer_settime(timer_t timer_id, int tmr_flags,
 
        if (old_spec64)
                memset(old_spec64, 0, sizeof(*old_spec64));
-retry:
+
        timr = lock_timer(timer_id, &flags);
+retry:
        if (!timr)
                return -EINVAL;
 
@@ -870,11 +882,14 @@ retry:
        else
                error = kc->timer_set(timr, tmr_flags, new_spec64, old_spec64);
 
-       unlock_timer(timr, flags);
        if (error == TIMER_RETRY) {
-               old_spec64 = NULL;      // We already got the old time...
+               // We already got the old time...
+               old_spec64 = NULL;
+               /* Unlocks and relocks the timer if it still exists */
+               timr = timer_wait_running(timr, &flags);
                goto retry;
        }
+       unlock_timer(timr, flags);
 
        return error;
 }
@@ -951,13 +966,15 @@ SYSCALL_DEFINE1(timer_delete, timer_t, timer_id)
        struct k_itimer *timer;
        unsigned long flags;
 
-retry_delete:
        timer = lock_timer(timer_id, &flags);
+
+retry_delete:
        if (!timer)
                return -EINVAL;
 
-       if (timer_delete_hook(timer) == TIMER_RETRY) {
-               unlock_timer(timer, flags);
+       if (unlikely(timer_delete_hook(timer) == TIMER_RETRY)) {
+               /* Unlocks and relocks the timer if it still exists */
+               timer = timer_wait_running(timer, &flags);
                goto retry_delete;
        }