The patch titled
cond_resched() fix
has been removed from the -mm tree. Its filename is
cond_resched-fix.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
Subject: cond_resched() fix
From: Andrew Morton <akpm@xxxxxxxx>
Fix a bug identified by Zou Nan hai <nanhai.zou@xxxxxxxxx>:
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@xxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/sched.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff -puN kernel/sched.c~cond_resched-fix kernel/sched.c
--- a/kernel/sched.c~cond_resched-fix
+++ a/kernel/sched.c
@@ -4386,7 +4386,16 @@ asmlinkage long sys_sched_yield(void)
return 0;
}
-static inline void __cond_resched(void)
+static inline int __resched_legal(void)
+{
+ if (unlikely(preempt_count()))
+ return 0;
+ if (unlikely(system_state != SYSTEM_RUNNING))
+ return 0;
+ return 1;
+}
+
+static void __cond_resched(void)
{
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
__might_sleep(__FILE__, __LINE__);
@@ -4396,10 +4405,6 @@ static inline void __cond_resched(void)
* 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();
@@ -4409,13 +4414,12 @@ static inline void __cond_resched(void)
int __sched cond_resched(void)
{
- if (need_resched()) {
+ if (need_resched() && __resched_legal()) {
__cond_resched();
return 1;
}
return 0;
}
-
EXPORT_SYMBOL(cond_resched);
/*
@@ -4436,7 +4440,7 @@ int cond_resched_lock(spinlock_t *lock)
ret = 1;
spin_lock(lock);
}
- if (need_resched()) {
+ if (need_resched() && __resched_legal()) {
_raw_spin_unlock(lock);
preempt_enable_no_resched();
__cond_resched();
@@ -4445,14 +4449,13 @@ 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()) {
__local_bh_enable();
__cond_resched();
local_bh_disable();
@@ -4460,10 +4463,8 @@ int __sched cond_resched_softirq(void)
}
return 0;
}
-
EXPORT_SYMBOL(cond_resched_softirq);
-
/**
* yield - yield the current processor to other threads.
*
_
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