summaryrefslogtreecommitdiff
path: root/include/linux/sched/wake_q.h
diff options
context:
space:
mode:
authorIngo Molnar <mingo@kernel.org>2017-02-01 19:09:06 +0300
committerIngo Molnar <mingo@kernel.org>2017-03-02 10:42:42 +0300
commiteb61baf69871b9836783a81bc451189edb0d9de2 (patch)
treee3758167461e9ada45b64ae282ecd7c818c0ca03 /include/linux/sched/wake_q.h
parent5dbe91de599423d243738a205367506444ebb4a4 (diff)
downloadlinux-eb61baf69871b9836783a81bc451189edb0d9de2.tar.xz
sched/headers: Move the wake-queue types and interfaces from sched.h into <linux/sched/wake_q.h>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/sched/wake_q.h')
-rw-r--r--include/linux/sched/wake_q.h47
1 files changed, 47 insertions, 0 deletions
diff --git a/include/linux/sched/wake_q.h b/include/linux/sched/wake_q.h
index 6383b35e4eba..d03d8a9047dc 100644
--- a/include/linux/sched/wake_q.h
+++ b/include/linux/sched/wake_q.h
@@ -1,6 +1,53 @@
#ifndef _LINUX_SCHED_WAKE_Q_H
#define _LINUX_SCHED_WAKE_Q_H
+/*
+ * Wake-queues are lists of tasks with a pending wakeup, whose
+ * callers have already marked the task as woken internally,
+ * and can thus carry on. A common use case is being able to
+ * do the wakeups once the corresponding user lock as been
+ * released.
+ *
+ * We hold reference to each task in the list across the wakeup,
+ * thus guaranteeing that the memory is still valid by the time
+ * the actual wakeups are performed in wake_up_q().
+ *
+ * One per task suffices, because there's never a need for a task to be
+ * in two wake queues simultaneously; it is forbidden to abandon a task
+ * in a wake queue (a call to wake_up_q() _must_ follow), so if a task is
+ * already in a wake queue, the wakeup will happen soon and the second
+ * waker can just skip it.
+ *
+ * The DEFINE_WAKE_Q macro declares and initializes the list head.
+ * wake_up_q() does NOT reinitialize the list; it's expected to be
+ * called near the end of a function. Otherwise, the list can be
+ * re-initialized for later re-use by wake_q_init().
+ *
+ * Note that this can cause spurious wakeups. schedule() callers
+ * must ensure the call is done inside a loop, confirming that the
+ * wakeup condition has in fact occurred.
+ */
+
#include <linux/sched.h>
+struct wake_q_head {
+ struct wake_q_node *first;
+ struct wake_q_node **lastp;
+};
+
+#define WAKE_Q_TAIL ((struct wake_q_node *) 0x01)
+
+#define DEFINE_WAKE_Q(name) \
+ struct wake_q_head name = { WAKE_Q_TAIL, &name.first }
+
+static inline void wake_q_init(struct wake_q_head *head)
+{
+ head->first = WAKE_Q_TAIL;
+ head->lastp = &head->first;
+}
+
+extern void wake_q_add(struct wake_q_head *head,
+ struct task_struct *task);
+extern void wake_up_q(struct wake_q_head *head);
+
#endif /* _LINUX_SCHED_WAKE_Q_H */