Messages in this thread Patch in this message | | | Subject | [PATCH RFC] sched/fair: fix sudden expiration of cfq quota in put_prev_task() | From | Konstantin Khlebnikov <> | Date | Fri, 03 Apr 2015 15:41:38 +0300 |
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Pick_next_task_fair() must be sure that here is at least one runnable task before calling put_prev_task(), but put_prev_task() can expire last remains of cfs quota and throttle all currently runnable tasks. As a result pick_next_task_fair() cannot find next task and crashes.
This patch leaves 1 in ->runtime_remaining when current assignation expires and tries to refill it right after that. In the worst case task will be scheduled once and throttled at the end of slice.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> --- kernel/sched/fair.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7ce18f3c097a..91785d077db4 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3447,11 +3447,12 @@ static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq) { struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg); - /* if the deadline is ahead of our clock, nothing to do */ - if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0)) + /* nothing to expire */ + if (cfs_rq->runtime_remaining <= 0) return; - if (cfs_rq->runtime_remaining < 0) + /* if the deadline is ahead of our clock, nothing to do */ + if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0)) return; /* @@ -3469,8 +3470,14 @@ static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq) /* extend local deadline, drift is bounded above by 2 ticks */ cfs_rq->runtime_expires += TICK_NSEC; } else { - /* global deadline is ahead, expiration has passed */ - cfs_rq->runtime_remaining = 0; + /* + * Global deadline is ahead, expiration has passed. + * + * Do not expire runtime completely. Otherwise put_prev_task() + * can throttle all tasks when we already checked nr_running or + * put_prev_entity() can throttle already chosen next entity. + */ + cfs_rq->runtime_remaining = 1; } } @@ -3480,7 +3487,7 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) cfs_rq->runtime_remaining -= delta_exec; expire_cfs_rq_runtime(cfs_rq); - if (likely(cfs_rq->runtime_remaining > 0)) + if (likely(cfs_rq->runtime_remaining > 1)) return; /*
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