[PATCH] fix cond_resched() fix

In cond_resched_lock() it calls __resched_legal() before dropping the spin
lock.  __resched_legal() will always finds the preempt_count non-zero and
will prevent the call to __cond_resched().

The attached patch adds a parameter to __resched_legal() with the expected
preempt_count value.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 41a571806ce0..de440b220b4c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4456,9 +4456,9 @@ asmlinkage long sys_sched_yield(void)
         return 0;
 }
 
-static inline int __resched_legal(void)
+static inline int __resched_legal(int expected_preempt_count)
 {
-        if (unlikely(preempt_count()))
+        if (unlikely(preempt_count() != expected_preempt_count))
                 return 0;
         if (unlikely(system_state != SYSTEM_RUNNING))
                 return 0;
@@ -4484,7 +4484,7 @@ static void __cond_resched(void)
 
 int __sched cond_resched(void)
 {
-        if (need_resched() && __resched_legal()) {
+        if (need_resched() && __resched_legal(0)) {
                 __cond_resched();
                 return 1;
         }
@@ -4510,7 +4510,7 @@ int cond_resched_lock(spinlock_t *lock)
                 ret = 1;
                 spin_lock(lock);
         }
-        if (need_resched() && __resched_legal()) {
+        if (need_resched() && __resched_legal(1)) {
                 spin_release(&lock->dep_map, 1, _THIS_IP_);
                 _raw_spin_unlock(lock);
                 preempt_enable_no_resched();
@@ -4526,7 +4526,7 @@ int __sched cond_resched_softirq(void)
 {
         BUG_ON(!in_softirq());
 
-        if (need_resched() && __resched_legal()) {
+        if (need_resched() && __resched_legal(0)) {
                 raw_local_irq_disable();
                 _local_bh_enable();
                 raw_local_irq_enable();