[PATCH 1/8] wait_event_interruptible_locked() interface

Michal Nazarewicz
2010-04-16T09:49:50Z

New wait_event_interruptible{,_exclusive}_locked{,_irq,_irqsave}
macros added. They work just like versions without _locked* suffix
but require the wait queue's lock to be held. Also __wake_up_locked()
is now exported as to pair it with the above macros.

The use case of this new facility is when one uses wait queue's lock
to protect a data structure. This may be advantageous if the
structure needs to be protected by a spinlock anyway. In particular,
with additional spinlock the following code has to be used to wait for
an condition:

spin_lock(&data.lock);
...
for (ret = 0; !ret && !(condition); ) {
spin_unlock(&data.lock);
ret = wait_event_interruptible(data.wqh, (condition));
spin_lock(&data.lock);
}
...
spin_unlock(&data.lock);

This looks bizarre plus wait_event_interruptible() locks the wait
queue's lock anyway so there is a unlock+lock sequence where it could
be avoided.

To avoid those problems and benefit from wait queue's lock, a code
similar to the following should be used:

/* Waiting */
spin_lock(&data.wqh.lock);
...
ret = wait_event_interruptible_locked(data.wqh, (condition));
...
spin_unlock(&data.wqh.lock);

/* Waiting exclusively */
spin_lock(&data.whq.lock);
...
ret = wait_event_interruptible_exclusive_locked(data.whq, (condition));
...
spin_unlock(&data.whq.lock);

/* Waking up */
spin_lock(&data.wqh.lock);
...
wake_up_locked(&data.wqh);
...
spin_unlock(&data.wqh.lock);

When spin_lock_irq() or spin_lock_irqsave() is used matching versions
of macros need to be used (*_locked_irq() or * _locked_irqsave()).

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
---
include/linux/wait.h | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched.c | 1 +
2 files changed, 150 insertions(+), 0 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index a48e16b..fc3c040 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -362,6 +362,155 @@ do { \
__ret; \
})

+
+#define __wait_event_interruptible_locked(wq, condition, exclusive, irq) \
+({ \
+ int __ret = 0; \
+ DEFINE_WAIT(__wait); \
+ if (exclusive) \
+ __wait.flags |= WQ_FLAG_EXCLUSIVE; \
+ do { \
+ if (likely(list_empty(&__wait.task_list))) \
+ __add_wait_queue_tail(&(wq), &__wait); \
+ set_current_state(TASK_INTERRUPTIBLE); \
+ if (signal_pending(current)) { \
+ __ret = -ERESTARTSYS; \
+ break; \
+ } \
+ if (irq) \
+ spin_unlock_irq(&(wq).lock); \
+ else \
+ spin_unlock(&(wq).lock); \
+ schedule(); \
+ if (irq) \
+ spin_lock_irq(&(wq).lock); \
+ else \
+ spin_lock(&(wq).lock); \
+ } while (!(condition)); \
+ __remove_wait_queue(&(wq), &__wait); \
+ __set_current_state(TASK_RUNNING); \
+ __ret; \
+})
+
+
+/**
+ * wait_event_interruptible_locked - sleep until a condition gets true
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * The process is put to sleep (TASK_INTERRUPTIBLE) until the
+ * @condition evaluates to true or a signal is received.
+ * The @condition is checked each time the waitqueue @wq is woken up.
+ *
+ * It must be called with wq.lock being held. This spinlock is
+ * unlocked while sleeping but @condition testing is done while lock
+ * is held and when this macro exits the lock is held.
+ *
+ * The lock is locked/unlocked using spin_lock()/spin_unlock()
+ * functions which must match the way they are locked/unlocked outside
+ * of this macro.
+ *
+ * wake_up_locked() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * The function will return -ERESTARTSYS if it was interrupted by a
+ * signal and 0 if @condition evaluated to true.
+ */
+#define wait_event_interruptible_locked(wq, condition) \
+ ((condition) \
+ ? 0 : __wait_event_interruptible_locked(wq, condition, 0, 0))
+
+/**
+ * wait_event_interruptible_locked_irq - sleep until a condition gets true
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * The process is put to sleep (TASK_INTERRUPTIBLE) until the
+ * @condition evaluates to true or a signal is received.
+ * The @condition is checked each time the waitqueue @wq is woken up.
+ *
+ * It must be called with wq.lock being held. This spinlock is
+ * unlocked while sleeping but @condition testing is done while lock
+ * is held and when this macro exits the lock is held.
+ *
+ * The lock is locked/unlocked using spin_lock_irq()/spin_unlock_irq()
+ * functions which must match the way they are locked/unlocked outside
+ * of this macro.
+ *
+ * wake_up_locked() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * The function will return -ERESTARTSYS if it was interrupted by a
+ * signal and 0 if @condition evaluated to true.
+ */
+#define wait_event_interruptible_locked_irq(wq, condition) \
+ ((condition) \
+ ? 0 : __wait_event_interruptible_locked(wq, condition, 0, 1))
+
+/**
+ * wait_event_interruptible_exclusive_locked - sleep exclusively until a condition gets true
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * The process is put to sleep (TASK_INTERRUPTIBLE) until the
+ * @condition evaluates to true or a signal is received.
+ * The @condition is checked each time the waitqueue @wq is woken up.
+ *
+ * It must be called with wq.lock being held. This spinlock is
+ * unlocked while sleeping but @condition testing is done while lock
+ * is held and when this macro exits the lock is held.
+ *
+ * The lock is locked/unlocked using spin_lock()/spin_unlock()
+ * functions which must match the way they are locked/unlocked outside
+ * of this macro.
+ *
+ * The process is put on the wait queue with an WQ_FLAG_EXCLUSIVE flag
+ * set thus when other process waits process on the list if this
+ * process is awaken further processes are not considered.
+ *
+ * wake_up_locked() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * The function will return -ERESTARTSYS if it was interrupted by a
+ * signal and 0 if @condition evaluated to true.
+ */
+#define wait_event_interruptible_exclusive_locked(wq, condition) \
+ ((condition) \
+ ? 0 : __wait_event_interruptible_locked(wq, condition, 1, 0))
+
+/**
+ * wait_event_interruptible_exclusive_locked_irq - sleep until a condition gets true
+ * @wq: the waitqueue to wait on
+ * @condition: a C expression for the event to wait for
+ *
+ * The process is put to sleep (TASK_INTERRUPTIBLE) until the
+ * @condition evaluates to true or a signal is received.
+ * The @condition is checked each time the waitqueue @wq is woken up.
+ *
+ * It must be called with wq.lock being held. This spinlock is
+ * unlocked while sleeping but @condition testing is done while lock
+ * is held and when this macro exits the lock is held.
+ *
+ * The lock is locked/unlocked using spin_lock_irq()/spin_unlock_irq()
+ * functions which must match the way they are locked/unlocked outside
+ * of this macro.
+ *
+ * The process is put on the wait queue with an WQ_FLAG_EXCLUSIVE flag
+ * set thus when other process waits process on the list if this
+ * process is awaken further processes are not considered.
+ *
+ * wake_up_locked() has to be called after changing any variable that could
+ * change the result of the wait condition.
+ *
+ * The function will return -ERESTARTSYS if it was interrupted by a
+ * signal and 0 if @condition evaluated to true.
+ */
+#define wait_event_interruptible_exclusive_locked_irq(wq, condition) \
+ ((condition) \
+ ? 0 : __wait_event_interruptible_locked(wq, condition, 1, 1))
+
+
+
#define __wait_event_killable(wq, condition, ret) \
do { \
DEFINE_WAIT(__wait); \
diff --git a/kernel/sched.c b/kernel/sched.c
index a3dff1f..69e1d32 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3940,6 +3940,7 @@ void __wake_up_locked(wait_queue_head_t *q, unsigned int mode)
{
__wake_up_common(q, mode, 1, 0, NULL);
}
+EXPORT_SYMBOL_GPL(__wake_up_locked);

void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
{
--
1.7.0