Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Two fixes: a guest-cputime accounting fix, and a cgroup bandwidth
  quota precision fix"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/vtime: Fix guest/system mis-accounting on task switch
  sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision

2 files changed, 25 insertions, 17 deletions

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 2305ce89a26c..46ed4e1383e2 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -740,7 +740,7 @@ void vtime_account_system(struct task_struct *tsk)
 
         write_seqcount_begin(&vtime->seqcount);
         /* We might have scheduled out from guest path */
-        if (current->flags & PF_VCPU)
+        if (tsk->flags & PF_VCPU)
                 vtime_account_guest(tsk, vtime);
         else
                 __vtime_account_system(tsk, vtime);
@@ -783,7 +783,7 @@ void vtime_guest_enter(struct task_struct *tsk)
          */
         write_seqcount_begin(&vtime->seqcount);
         __vtime_account_system(tsk, vtime);
-        current->flags |= PF_VCPU;
+        tsk->flags |= PF_VCPU;
         write_seqcount_end(&vtime->seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_enter);
@@ -794,7 +794,7 @@ void vtime_guest_exit(struct task_struct *tsk)
 
         write_seqcount_begin(&vtime->seqcount);
         vtime_account_guest(tsk, vtime);
-        current->flags &= ~PF_VCPU;
+        tsk->flags &= ~PF_VCPU;
         write_seqcount_end(&vtime->seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_exit);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 83ab35e2374f..682a754ea3e1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4926,20 +4926,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
                 if (++count > 3) {
                         u64 new, old = ktime_to_ns(cfs_b->period);
 
-                        new = (old * 147) / 128; /* ~115% */
-                        new = min(new, max_cfs_quota_period);
-
-                        cfs_b->period = ns_to_ktime(new);
-
-                        /* since max is 1s, this is limited to 1e9^2, which fits in u64 */
-                        cfs_b->quota *= new;
-                        cfs_b->quota = div64_u64(cfs_b->quota, old);
-
-                        pr_warn_ratelimited(
-        "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n",
-                                smp_processor_id(),
-                                div_u64(new, NSEC_PER_USEC),
-                                div_u64(cfs_b->quota, NSEC_PER_USEC));
+                        /*
+                         * Grow period by a factor of 2 to avoid losing precision.
+                         * Precision loss in the quota/period ratio can cause __cfs_schedulable
+                         * to fail.
+                         */
+                        new = old * 2;
+                        if (new < max_cfs_quota_period) {
+                                cfs_b->period = ns_to_ktime(new);
+                                cfs_b->quota *= 2;
+
+                                pr_warn_ratelimited(
+        "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us = %lld, cfs_quota_us = %lld)\n",
+                                        smp_processor_id(),
+                                        div_u64(new, NSEC_PER_USEC),
+                                        div_u64(cfs_b->quota, NSEC_PER_USEC));
+                        } else {
+                                pr_warn_ratelimited(
+        "cfs_period_timer[cpu%d]: period too short, but cannot scale up without losing precision (cfs_period_us = %lld, cfs_quota_us = %lld)\n",
+                                        smp_processor_id(),
+                                        div_u64(old, NSEC_PER_USEC),
+                                        div_u64(cfs_b->quota, NSEC_PER_USEC));
+                        }
 
                         /* reset count so we don't come right back in here */
                         count = 0;