summaryrefslogtreecommitdiffstats
path: root/kernel/sched
diff options
context:
space:
mode:
authorBen Segall <bsegall@google.com>2014-05-19 15:49:45 -0700
committerIngo Molnar <mingo@kernel.org>2014-06-05 11:52:00 +0200
commit51f2176d74ace4c3f58579a605ef5a9720befb00 (patch)
tree3c4f8405eacae93ef43707c2d335f8a12212eaeb /kernel/sched
parent096aa33863a5e48de52d2ff30e0801b7487944f4 (diff)
downloadop-kernel-dev-51f2176d74ace4c3f58579a605ef5a9720befb00.zip
op-kernel-dev-51f2176d74ace4c3f58579a605ef5a9720befb00.tar.gz
sched/fair: Fix unlocked reads of some cfs_b->quota/period
sched_cfs_period_timer() reads cfs_b->period without locks before calling do_sched_cfs_period_timer(), and similarly unthrottle_offline_cfs_rqs() would read cfs_b->period without the right lock. Thus a simultaneous change of bandwidth could cause corruption on any platform where ktime_t or u64 writes/reads are not atomic. Extend cfs_b->lock from do_sched_cfs_period_timer() to include the read of cfs_b->period to solve that issue; unthrottle_offline_cfs_rqs() can just use 1 rather than the exact quota, much like distribute_cfs_runtime() does. There is also an unlocked read of cfs_b->runtime_expires, but a race there would only delay runtime expiry by a tick. Still, the comparison should just be != anyway, which clarifies even that problem. Signed-off-by: Ben Segall <bsegall@google.com> Tested-by: Roman Gushchin <klamm@yandex-team.ru> [peterz: Fix compile warn] Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20140519224945.20303.93530.stgit@sword-of-the-dawn.mtv.corp.google.com Cc: pjt@google.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c40
1 files changed, 21 insertions, 19 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c9617b7..b71d8c3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3224,10 +3224,12 @@ 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 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 ((s64)(cfs_rq->runtime_expires - cfs_b->runtime_expires) >= 0) {
+ 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 {
@@ -3456,21 +3458,21 @@ next:
static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
{
u64 runtime, runtime_expires;
- int idle = 1, throttled;
+ int throttled;
- raw_spin_lock(&cfs_b->lock);
/* no need to continue the timer with no bandwidth constraint */
if (cfs_b->quota == RUNTIME_INF)
- goto out_unlock;
+ goto out_deactivate;
throttled = !list_empty(&cfs_b->throttled_cfs_rq);
- /* idle depends on !throttled (for the case of a large deficit) */
- idle = cfs_b->idle && !throttled;
cfs_b->nr_periods += overrun;
- /* if we're going inactive then everything else can be deferred */
- if (idle)
- goto out_unlock;
+ /*
+ * idle depends on !throttled (for the case of a large deficit), and if
+ * we're going inactive then everything else can be deferred
+ */
+ if (cfs_b->idle && !throttled)
+ goto out_deactivate;
/*
* if we have relooped after returning idle once, we need to update our
@@ -3484,7 +3486,7 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
if (!throttled) {
/* mark as potentially idle for the upcoming period */
cfs_b->idle = 1;
- goto out_unlock;
+ return 0;
}
/* account preceding periods in which throttling occurred */
@@ -3524,12 +3526,12 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
* timer to remain active while there are any throttled entities.)
*/
cfs_b->idle = 0;
-out_unlock:
- if (idle)
- cfs_b->timer_active = 0;
- raw_spin_unlock(&cfs_b->lock);
- return idle;
+ return 0;
+
+out_deactivate:
+ cfs_b->timer_active = 0;
+ return 1;
}
/* a cfs_rq won't donate quota below this amount */
@@ -3706,6 +3708,7 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
int overrun;
int idle = 0;
+ raw_spin_lock(&cfs_b->lock);
for (;;) {
now = hrtimer_cb_get_time(timer);
overrun = hrtimer_forward(timer, now, cfs_b->period);
@@ -3715,6 +3718,7 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
idle = do_sched_cfs_period_timer(cfs_b, overrun);
}
+ raw_spin_unlock(&cfs_b->lock);
return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}
@@ -3774,8 +3778,6 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
struct cfs_rq *cfs_rq;
for_each_leaf_cfs_rq(rq, cfs_rq) {
- struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
-
if (!cfs_rq->runtime_enabled)
continue;
@@ -3783,7 +3785,7 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
* clock_task is not advancing so we just need to make sure
* there's some valid quota amount
*/
- cfs_rq->runtime_remaining = cfs_b->quota;
+ cfs_rq->runtime_remaining = 1;
if (cfs_rq_throttled(cfs_rq))
unthrottle_cfs_rq(cfs_rq);
}
OpenPOWER on IntegriCloud