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authorAndrew Morton <akpm@osdl.org>2006-07-28 22:52:09 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2006-08-06 20:52:16 -0700
commitfed0a6b6fb78cd432863f29e83a458c9fd13a308 (patch)
tree7347e3962c19f346cbb9f8ca7190fc51ec1a5eb8
parentaccdd0e1f5080ec98f7bf87c5a8b255539e1ab4b (diff)
cond_resched() fix
Fix a bug identified by Zou Nan hai <nanhai.zou@intel.com>: If the system is in state SYSTEM_BOOTING, and need_resched() is true, cond_resched() returns true even though it didn't reschedule. Consequently need_resched() remains true and JBD locks up. Fix that by teaching cond_resched() to only return true if it really did call schedule(). cond_resched_lock() and cond_resched_softirq() have a problem too. If we're in SYSTEM_BOOTING state and need_resched() is true, these functions will drop the lock and will then try to call schedule(), but the SYSTEM_BOOTING state will prevent schedule() from being called. So on return, need_resched() will still be true, but cond_resched_lock() has to return 1 to tell the caller that the lock was dropped. The caller will probably lock up. Bottom line: if these functions dropped the lock, they _must_ call schedule() to clear need_resched(). Make it so. Also, uninline __cond_resched(). It's largeish, and slowpath. Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--kernel/sched.c25
1 files changed, 13 insertions, 12 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index c13f1bd2df7d..61d11691a629 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4044,17 +4044,22 @@ asmlinkage long sys_sched_yield(void)
return 0;
}
-static inline void __cond_resched(void)
+static inline int __resched_legal(int expected_preempt_count)
+{
+ if (unlikely(preempt_count() != expected_preempt_count))
+ return 0;
+ if (unlikely(system_state != SYSTEM_RUNNING))
+ return 0;
+ return 1;
+}
+
+static void __cond_resched(void)
{
/*
* The BKS might be reacquired before we have dropped
* PREEMPT_ACTIVE, which could trigger a second
* cond_resched() call.
*/
- if (unlikely(preempt_count()))
- return;
- if (unlikely(system_state != SYSTEM_RUNNING))
- return;
do {
add_preempt_count(PREEMPT_ACTIVE);
schedule();
@@ -4064,13 +4069,12 @@ static inline void __cond_resched(void)
int __sched cond_resched(void)
{
- if (need_resched()) {
+ if (need_resched() && __resched_legal(0)) {
__cond_resched();
return 1;
}
return 0;
}
-
EXPORT_SYMBOL(cond_resched);
/*
@@ -4091,7 +4095,7 @@ int cond_resched_lock(spinlock_t *lock)
ret = 1;
spin_lock(lock);
}
- if (need_resched()) {
+ if (need_resched() && __resched_legal(1)) {
_raw_spin_unlock(lock);
preempt_enable_no_resched();
__cond_resched();
@@ -4100,14 +4104,13 @@ int cond_resched_lock(spinlock_t *lock)
}
return ret;
}
-
EXPORT_SYMBOL(cond_resched_lock);
int __sched cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
- if (need_resched()) {
+ if (need_resched() && __resched_legal(0)) {
__local_bh_enable();
__cond_resched();
local_bh_disable();
@@ -4115,10 +4118,8 @@ int __sched cond_resched_softirq(void)
}
return 0;
}
-
EXPORT_SYMBOL(cond_resched_softirq);
-
/**
* yield - yield the current processor to other threads.
*