Messages in this thread Patch in this message | | | Date | Wed, 30 Sep 2015 09:10:37 +0200 | From | Peter Zijlstra <> | Subject | [PATCH v2 02/12] sched: Rework TASK_DEAD preemption exception |
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TASK_DEAD is special in that the final schedule call from do_exit() must be done with preemption disabled.
This means we end up scheduling with a preempt_count() higher than usual (3 instead of the 'expected' 2). Since future patches will want to rely on an invariant preempt_count() value during schedule, fix this up.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/sched/core.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2949,12 +2949,8 @@ static inline void schedule_debug(struct #ifdef CONFIG_SCHED_STACK_END_CHECK BUG_ON(unlikely(task_stack_end_corrupted(prev))); #endif - /* - * Test if we are atomic. Since do_exit() needs to call into - * schedule() atomically, we ignore that path. Otherwise whine - * if we are scheduling when we should not. - */ - if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) + + if (unlikely(in_atomic_preempt_off())) __schedule_bug(prev); rcu_sleep_check(); @@ -3053,6 +3049,17 @@ static void __sched __schedule(void) rcu_note_context_switch(); prev = rq->curr; + /* + * do_exit() calls schedule() with preemption disabled as an exception; + * however we must fix that up, otherwise the next task will see an + * inconsistent (higher) preempt count. + * + * It also avoids the below schedule_debug() test from complaining + * about this. + */ + if (unlikely(prev->state == TASK_DEAD)) + preempt_enable_no_resched_notrace(); + schedule_debug(prev); if (sched_feat(HRTICK))
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