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Commit b99def8b authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/core: Rework TASK_DEAD preemption exception 



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.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 87dcbc06

kernel/sched/core.c

+13 −6
Original line number Diff line number Diff line
@@ -2949,12 +2949,8 @@ static inline void schedule_debug(struct task_struct *prev) 
#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))