Revert "sched/fair: Fix bandwidth timer clock drift condition"

This reverts commit eb29ee5a3873134917a760bf9c416da0a089a0be, which
was commit 512ac999d2755d2b7109e996a76b6fb8b888631d upstream.  This
introduced a regression and doesn't seem to have been suitable for
older stable branches.  (It has been fixed differently upstream.)

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 773135f534ef2b596fdac3511de70c61f921d332..e17c063a802807421498732efb19366215b2886d 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3163,7 +3163,6 @@ void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
        now = sched_clock_cpu(smp_processor_id());
        cfs_b->runtime = cfs_b->quota;
        cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
-       cfs_b->expires_seq++;
 }
 
 static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
@@ -3186,7 +3185,6 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
        struct task_group *tg = cfs_rq->tg;
        struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
        u64 amount = 0, min_amount, expires;
-       int expires_seq;
 
        /* note: this is a positive sum as runtime_remaining <= 0 */
        min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;
@@ -3212,7 +3210,6 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
                        cfs_b->idle = 0;
                }
        }
-       expires_seq = cfs_b->expires_seq;
        expires = cfs_b->runtime_expires;
        raw_spin_unlock(&cfs_b->lock);
 
@@ -3222,10 +3219,8 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
         * spread between our sched_clock and the one on which runtime was
         * issued.
         */
-       if (cfs_rq->expires_seq != expires_seq) {
-               cfs_rq->expires_seq = expires_seq;
+       if ((s64)(expires - cfs_rq->runtime_expires) > 0)
                cfs_rq->runtime_expires = expires;
-       }
 
        return cfs_rq->runtime_remaining > 0;
 }
@@ -3251,9 +3246,12 @@ static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
         * has not truly expired.
         *
         * Fortunately we can check determine whether this the case by checking
-        * whether the global deadline(cfs_b->expires_seq) has advanced.
+        * whether the global deadline has advanced. It is valid to compare
+        * cfs_b->runtime_expires without any locks since we only care about
+        * exact equality, so a partial write will still work.
         */
-       if (cfs_rq->expires_seq == cfs_b->expires_seq) {
+
+       if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
                /* extend local deadline, drift is bounded above by 2 ticks */
                cfs_rq->runtime_expires += TICK_NSEC;
        } else {

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 41e3547263d4bf268ef40e416308785e83d36f88..a4f5c7540cf2dc1442ce78a91e7fce3cc2dda874 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -187,7 +187,6 @@ struct cfs_bandwidth {
        u64 quota, runtime;
        s64 hierarchal_quota;
        u64 runtime_expires;
-       int expires_seq;
 
        int idle, timer_active;
        struct hrtimer period_timer, slack_timer;
@@ -377,7 +376,6 @@ struct cfs_rq {
 
 #ifdef CONFIG_CFS_BANDWIDTH
        int runtime_enabled;
-       int expires_seq;
        u64 runtime_expires;
        s64 runtime_remaining;