[PATCH] sched: fix cond_resched_softirq() offset (9414232f) · Commits · 戴 / test

Remove the __resched_legal() check: it is conceptually broken. The biggest problem it had is that it can mask buggy cond_resched() calls. A cond_resched() call is only legal if we are not in an atomic context, with two narrow exceptions: - if the system is booting - a reacquire_kernel_lock() down() done while PREEMPT_ACTIVE is set But __resched_legal() hid this and just silently returned whenever these primitives were called from invalid contexts. (Same goes for cond_resched_locked() and cond_resched_softirq()). Furthermore, the __legal_resched(0) call was buggy in that it caused unnecessarily long softirq latencies via cond_resched_softirq(). (which is only called from softirq-off sections, hence the code did nothing.) The fix is to resurrect the efficiency of the might_sleep checks and to only allow the narrow exceptions. Signed-off-by:

Ingo Molnar <mingo@elte.hu> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

+4 −14

Original line number	Diff line number	Diff line
		@@ -4617,17 +4617,6 @@ asmlinkage long sys_sched_yield(void)
		return 0;
		}

		static inline int __resched_legal(int expected_preempt_count)
		{
		#ifdef CONFIG_PREEMPT
		if (unlikely(preempt_count() != expected_preempt_count))
		return 0;
		#endif
		if (unlikely(system_state != SYSTEM_RUNNING))
		return 0;
		return 1;
		}

		static void __cond_resched(void)
		{
		#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
		@@ -4647,7 +4636,8 @@ static void __cond_resched(void)

		int __sched cond_resched(void)
		{
		if (need_resched() && __resched_legal(0)) {
		if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
		system_state == SYSTEM_RUNNING) {
		__cond_resched();
		return 1;
		}
		@@ -4673,7 +4663,7 @@ int cond_resched_lock(spinlock_t *lock)
		ret = 1;
		spin_lock(lock);
		}
		if (need_resched() && __resched_legal(1)) {
		if (need_resched() && system_state == SYSTEM_RUNNING) {
		spin_release(&lock->dep_map, 1, _THIS_IP_);
		_raw_spin_unlock(lock);
		preempt_enable_no_resched();
		@@ -4689,7 +4679,7 @@ int __sched cond_resched_softirq(void)
		{
		BUG_ON(!in_softirq());

		if (need_resched() && __resched_legal(0)) {
		if (need_resched() && system_state == SYSTEM_RUNNING) {
		raw_local_irq_disable();
		_local_bh_enable();
		raw_local_irq_enable();

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