[RFC][PATCH 4/6] implicit vs explicit preempt_disable()

From: Peter Zijlstra
Date: Wed Sep 19 2007 - 06:53:54 EST

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In reply to: Peter Zijlstra: "[RFC][PATCH 6/6] fixup early boot"
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Decouple preempt_disable() from the locking primitives, so as that we
can test for proper rcu_dereference() context regardless of the locking
model.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
include/linux/preempt.h | 37 +++++++++++++++++++----
kernel/sched.c | 10 +++---
kernel/spinlock.c | 76 ++++++++++++++++++++++++------------------------
lib/kernel_lock.c | 16 +++++-----
4 files changed, 82 insertions(+), 57 deletions(-)

Index: linux-2.6/include/linux/preempt.h
===================================================================
--- linux-2.6.orig/include/linux/preempt.h
+++ linux-2.6/include/linux/preempt.h
@@ -30,6 +30,33 @@

asmlinkage void preempt_schedule(void);

+#define preempt_check_resched() \
+do { \
+ if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
+ preempt_schedule(); \
+} while (0)
+
+
+#define _preempt_disable() \
+do { \
+ __add_preempt_count(1, 0); \
+ barrier(); \
+} while (0)
+
+#define _preempt_enable_no_resched() \
+do { \
+ barrier(); \
+ __sub_preempt_count(1, 0); \
+} while (0)
+
+#define _preempt_enable() \
+do { \
+ _preempt_enable_no_resched(); \
+ barrier(); \
+ preempt_check_resched(); \
+} while (0)
+
+
#define preempt_disable() \
do { \
__add_preempt_count(1, 1); \
@@ -42,12 +69,6 @@ do { \
__sub_preempt_count(1, 1); \
} while (0)

-#define preempt_check_resched() \
-do { \
- if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
- preempt_schedule(); \
-} while (0)
-
#define preempt_enable() \
do { \
preempt_enable_no_resched(); \
@@ -57,6 +78,10 @@ do { \

#else

+#define _preempt_disable() do { } while (0)
+#define _preempt_enable_no_resched() do { } while (0)
+#define _preempt_enable() do { } while (0)
+
#define preempt_disable() do { } while (0)
#define preempt_enable_no_resched() do { } while (0)
#define preempt_enable() do { } while (0)
Index: linux-2.6/kernel/spinlock.c
===================================================================
--- linux-2.6.orig/kernel/spinlock.c
+++ linux-2.6/kernel/spinlock.c
@@ -23,39 +23,39 @@

int __lockfunc _spin_trylock(spinlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
if (_raw_spin_trylock(lock)) {
spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
return 1;
}

- preempt_enable();
+ _preempt_enable();
return 0;
}
EXPORT_SYMBOL(_spin_trylock);

int __lockfunc _read_trylock(rwlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
if (_raw_read_trylock(lock)) {
rwlock_acquire_read(&lock->dep_map, 0, 1, _RET_IP_);
return 1;
}

- preempt_enable();
+ _preempt_enable();
return 0;
}
EXPORT_SYMBOL(_read_trylock);

int __lockfunc _write_trylock(rwlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
if (_raw_write_trylock(lock)) {
rwlock_acquire(&lock->dep_map, 0, 1, _RET_IP_);
return 1;
}

- preempt_enable();
+ _preempt_enable();
return 0;
}
EXPORT_SYMBOL(_write_trylock);
@@ -70,7 +70,7 @@ EXPORT_SYMBOL(_write_trylock);

void __lockfunc _read_lock(rwlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_read_trylock, _raw_read_lock);
}
@@ -81,7 +81,7 @@ unsigned long __lockfunc _spin_lock_irqs
unsigned long flags;

local_irq_save(flags);
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
/*
* On lockdep we dont want the hand-coded irq-enable of
@@ -100,7 +100,7 @@ EXPORT_SYMBOL(_spin_lock_irqsave);
void __lockfunc _spin_lock_irq(spinlock_t *lock)
{
local_irq_disable();
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
}
@@ -109,7 +109,7 @@ EXPORT_SYMBOL(_spin_lock_irq);
void __lockfunc _spin_lock_bh(spinlock_t *lock)
{
local_bh_disable();
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
}
@@ -120,7 +120,7 @@ unsigned long __lockfunc _read_lock_irqs
unsigned long flags;

local_irq_save(flags);
- preempt_disable();
+ _preempt_disable();
rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_read_trylock, _raw_read_lock);
return flags;
@@ -130,7 +130,7 @@ EXPORT_SYMBOL(_read_lock_irqsave);
void __lockfunc _read_lock_irq(rwlock_t *lock)
{
local_irq_disable();
- preempt_disable();
+ _preempt_disable();
rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_read_trylock, _raw_read_lock);
}
@@ -139,7 +139,7 @@ EXPORT_SYMBOL(_read_lock_irq);
void __lockfunc _read_lock_bh(rwlock_t *lock)
{
local_bh_disable();
- preempt_disable();
+ _preempt_disable();
rwlock_acquire_read(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_read_trylock, _raw_read_lock);
}
@@ -150,7 +150,7 @@ unsigned long __lockfunc _write_lock_irq
unsigned long flags;

local_irq_save(flags);
- preempt_disable();
+ _preempt_disable();
rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_write_trylock, _raw_write_lock);
return flags;
@@ -160,7 +160,7 @@ EXPORT_SYMBOL(_write_lock_irqsave);
void __lockfunc _write_lock_irq(rwlock_t *lock)
{
local_irq_disable();
- preempt_disable();
+ _preempt_disable();
rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_write_trylock, _raw_write_lock);
}
@@ -169,7 +169,7 @@ EXPORT_SYMBOL(_write_lock_irq);
void __lockfunc _write_lock_bh(rwlock_t *lock)
{
local_bh_disable();
- preempt_disable();
+ _preempt_disable();
rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_write_trylock, _raw_write_lock);
}
@@ -177,7 +177,7 @@ EXPORT_SYMBOL(_write_lock_bh);

void __lockfunc _spin_lock(spinlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
}
@@ -186,7 +186,7 @@ EXPORT_SYMBOL(_spin_lock);

void __lockfunc _write_lock(rwlock_t *lock)
{
- preempt_disable();
+ _preempt_disable();
rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_write_trylock, _raw_write_lock);
}
@@ -207,10 +207,10 @@ EXPORT_SYMBOL(_write_lock);
void __lockfunc _##op##_lock(locktype##_t *lock) \
{ \
for (;;) { \
- preempt_disable(); \
+ _preempt_disable(); \
if (likely(_raw_##op##_trylock(lock))) \
break; \
- preempt_enable(); \
+ _preempt_enable(); \
\
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
@@ -227,12 +227,12 @@ unsigned long __lockfunc _##op##_lock_ir
unsigned long flags; \
\
for (;;) { \
- preempt_disable(); \
+ _preempt_disable(); \
local_irq_save(flags); \
if (likely(_raw_##op##_trylock(lock))) \
break; \
local_irq_restore(flags); \
- preempt_enable(); \
+ _preempt_enable(); \
\
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
@@ -287,7 +287,7 @@ BUILD_LOCK_OPS(write, rwlock);

void __lockfunc _spin_lock_nested(spinlock_t *lock, int subclass)
{
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
}
@@ -298,7 +298,7 @@ unsigned long __lockfunc _spin_lock_irqs
unsigned long flags;

local_irq_save(flags);
- preempt_disable();
+ _preempt_disable();
spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
/*
* On lockdep we dont want the hand-coded irq-enable of
@@ -321,7 +321,7 @@ void __lockfunc _spin_unlock(spinlock_t
{
spin_release(&lock->dep_map, 1, _RET_IP_);
_raw_spin_unlock(lock);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_spin_unlock);

@@ -329,7 +329,7 @@ void __lockfunc _write_unlock(rwlock_t *
{
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_write_unlock(lock);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_write_unlock);

@@ -337,7 +337,7 @@ void __lockfunc _read_unlock(rwlock_t *l
{
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_read_unlock(lock);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_read_unlock);

@@ -346,7 +346,7 @@ void __lockfunc _spin_unlock_irqrestore(
spin_release(&lock->dep_map, 1, _RET_IP_);
_raw_spin_unlock(lock);
local_irq_restore(flags);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_spin_unlock_irqrestore);

@@ -355,7 +355,7 @@ void __lockfunc _spin_unlock_irq(spinloc
spin_release(&lock->dep_map, 1, _RET_IP_);
_raw_spin_unlock(lock);
local_irq_enable();
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_spin_unlock_irq);

@@ -363,7 +363,7 @@ void __lockfunc _spin_unlock_bh(spinlock
{
spin_release(&lock->dep_map, 1, _RET_IP_);
_raw_spin_unlock(lock);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
local_bh_enable_ip((unsigned long)__builtin_return_address(0));
}
EXPORT_SYMBOL(_spin_unlock_bh);
@@ -373,7 +373,7 @@ void __lockfunc _read_unlock_irqrestore(
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_read_unlock(lock);
local_irq_restore(flags);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_read_unlock_irqrestore);

@@ -382,7 +382,7 @@ void __lockfunc _read_unlock_irq(rwlock_
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_read_unlock(lock);
local_irq_enable();
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_read_unlock_irq);

@@ -390,7 +390,7 @@ void __lockfunc _read_unlock_bh(rwlock_t
{
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_read_unlock(lock);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
local_bh_enable_ip((unsigned long)__builtin_return_address(0));
}
EXPORT_SYMBOL(_read_unlock_bh);
@@ -400,7 +400,7 @@ void __lockfunc _write_unlock_irqrestore
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_write_unlock(lock);
local_irq_restore(flags);
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_write_unlock_irqrestore);

@@ -409,7 +409,7 @@ void __lockfunc _write_unlock_irq(rwlock
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_write_unlock(lock);
local_irq_enable();
- preempt_enable();
+ _preempt_enable();
}
EXPORT_SYMBOL(_write_unlock_irq);

@@ -417,7 +417,7 @@ void __lockfunc _write_unlock_bh(rwlock_
{
rwlock_release(&lock->dep_map, 1, _RET_IP_);
_raw_write_unlock(lock);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
local_bh_enable_ip((unsigned long)__builtin_return_address(0));
}
EXPORT_SYMBOL(_write_unlock_bh);
@@ -425,13 +425,13 @@ EXPORT_SYMBOL(_write_unlock_bh);
int __lockfunc _spin_trylock_bh(spinlock_t *lock)
{
local_bh_disable();
- preempt_disable();
+ _preempt_disable();
if (_raw_spin_trylock(lock)) {
spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
return 1;
}

- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
local_bh_enable_ip((unsigned long)__builtin_return_address(0));
return 0;
}
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -1847,7 +1847,7 @@ asmlinkage void schedule_tail(struct tas
finish_task_switch(rq, prev);
#ifdef __ARCH_WANT_UNLOCKED_CTXSW
/* In this case, finish_task_switch does not reenable preemption */
- preempt_enable();
+ _preempt_enable();
#endif
if (current->set_child_tid)
put_user(task_pid_vnr(current), current->set_child_tid);
@@ -3512,7 +3512,7 @@ asmlinkage void __sched schedule(void)
int cpu;

need_resched:
- preempt_disable();
+ _preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_qsctr_inc(cpu);
@@ -3560,7 +3560,7 @@ need_resched_nonpreemptible:
rq = cpu_rq(cpu);
goto need_resched_nonpreemptible;
}
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;
}
@@ -4605,7 +4605,7 @@ asmlinkage long sys_sched_yield(void)
__release(rq->lock);
spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
_raw_spin_unlock(&rq->lock);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();

schedule();

@@ -4661,7 +4661,7 @@ int cond_resched_lock(spinlock_t *lock)
if (need_resched() && system_state == SYSTEM_RUNNING) {
spin_release(&lock->dep_map, 1, _THIS_IP_);
_raw_spin_unlock(lock);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
__cond_resched();
ret = 1;
spin_lock(lock);
Index: linux-2.6/lib/kernel_lock.c
===================================================================
--- linux-2.6.orig/lib/kernel_lock.c
+++ linux-2.6/lib/kernel_lock.c
@@ -44,11 +44,11 @@ int __lockfunc __reacquire_kernel_lock(v
BUG_ON(saved_lock_depth < 0);

task->lock_depth = -1;
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();

down(&kernel_sem);

- preempt_disable();
+ _preempt_disable();
task->lock_depth = saved_lock_depth;

return 0;
@@ -121,14 +121,14 @@ int __lockfunc __reacquire_kernel_lock(v
return -EAGAIN;
cpu_relax();
}
- preempt_disable();
+ _preempt_disable();
return 0;
}

void __lockfunc __release_kernel_lock(void)
{
_raw_spin_unlock(&kernel_flag);
- preempt_enable_no_resched();
+ _preempt_enable_no_resched();
}

/*
@@ -139,7 +139,7 @@ void __lockfunc __release_kernel_lock(vo
#ifdef CONFIG_PREEMPT
static inline void __lock_kernel(void)
{
- preempt_disable();
+ _preempt_disable();
if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
/*
* If preemption was disabled even before this
@@ -156,10 +156,10 @@ static inline void __lock_kernel(void)
* with preemption enabled..
*/
do {
- preempt_enable();
+ _preempt_enable();
while (spin_is_locked(&kernel_flag))
cpu_relax();
- preempt_disable();
+ _preempt_disable();
} while (!_raw_spin_trylock(&kernel_flag));
}
}
@@ -182,7 +182,7 @@ static inline void __unlock_kernel(void)
* unlocking sequence (and thus avoid the dep-chain ops):
*/
_raw_spin_unlock(&kernel_flag);
- preempt_enable();
+ _preempt_enable();
}

/*

--

-
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Next message: Peter Zijlstra: "[RFC][PATCH 1/6] lockdep: annotate rcu_read_{,un}lock{,_bh}"
Previous message: Ian Campbell: "Re: [PATCH 3/3] Time to make CONFIG_PARAVIRT non-experimental."
In reply to: Peter Zijlstra: "[RFC][PATCH 6/6] fixup early boot"
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