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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: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Steven 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: Ingo Molnar <mingo@kernel.org>
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1 changed files with 13 additions and 6 deletions
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@ -2949,12 +2949,8 @@ static inline void schedule_debug(struct task_struct *prev)
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#ifdef CONFIG_SCHED_STACK_END_CHECK
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BUG_ON(unlikely(task_stack_end_corrupted(prev)));
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#endif
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/*
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* Test if we are atomic. Since do_exit() needs to call into
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* schedule() atomically, we ignore that path. Otherwise whine
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* if we are scheduling when we should not.
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*/
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if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
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if (unlikely(in_atomic_preempt_off()))
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__schedule_bug(prev);
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rcu_sleep_check();
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@ -3053,6 +3049,17 @@ static void __sched __schedule(void)
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rcu_note_context_switch();
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prev = rq->curr;
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/*
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* do_exit() calls schedule() with preemption disabled as an exception;
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* however we must fix that up, otherwise the next task will see an
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* inconsistent (higher) preempt count.
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*
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* It also avoids the below schedule_debug() test from complaining
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* about this.
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*/
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if (unlikely(prev->state == TASK_DEAD))
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preempt_enable_no_resched_notrace();
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schedule_debug(prev);
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if (sched_feat(HRTICK))
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