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authorPeter Zijlstra <peterz@infradead.org>2014-09-24 10:18:47 +0200
committerIngo Molnar <mingo@kernel.org>2014-10-28 10:55:15 +0100
commit61ada528dea028331e99e8ceaed87c683ad25de2 (patch)
tree0037fc75e3629576238dce932babf7738e80cb86 /kernel/sched
parent6f942a1f264e875c5f3ad6f505d7b500a3e7fa82 (diff)
sched/wait: Provide infrastructure to deal with nested blocking
There are a few places that call blocking primitives from wait loops, provide infrastructure to support this without the typical task_struct::state collision. We record the wakeup in wait_queue_t::flags which leaves task_struct::state free to be used by others. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Cc: tglx@linutronix.de Cc: ilya.dryomov@inktank.com Cc: umgwanakikbuti@gmail.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20140924082242.051202318@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/wait.c61
1 files changed, 61 insertions, 0 deletions
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 5a62915f47a8..4dae1885db6f 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -297,6 +297,67 @@ int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *
}
EXPORT_SYMBOL(autoremove_wake_function);
+
+/*
+ * DEFINE_WAIT_FUNC(wait, woken_wake_func);
+ *
+ * add_wait_queue(&wq, &wait);
+ * for (;;) {
+ * if (condition)
+ * break;
+ *
+ * p->state = mode; condition = true;
+ * smp_mb(); // A smp_wmb(); // C
+ * if (!wait->flags & WQ_FLAG_WOKEN) wait->flags |= WQ_FLAG_WOKEN;
+ * schedule() try_to_wake_up();
+ * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
+ * wait->flags &= ~WQ_FLAG_WOKEN; condition = true;
+ * smp_mb() // B smp_wmb(); // C
+ * wait->flags |= WQ_FLAG_WOKEN;
+ * }
+ * remove_wait_queue(&wq, &wait);
+ *
+ */
+long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
+{
+ set_current_state(mode); /* A */
+ /*
+ * The above implies an smp_mb(), which matches with the smp_wmb() from
+ * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
+ * also observe all state before the wakeup.
+ */
+ if (!(wait->flags & WQ_FLAG_WOKEN))
+ timeout = schedule_timeout(timeout);
+ __set_current_state(TASK_RUNNING);
+
+ /*
+ * The below implies an smp_mb(), it too pairs with the smp_wmb() from
+ * woken_wake_function() such that we must either observe the wait
+ * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
+ * an event.
+ */
+ set_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
+
+ return timeout;
+}
+EXPORT_SYMBOL(wait_woken);
+
+int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ /*
+ * Although this function is called under waitqueue lock, LOCK
+ * doesn't imply write barrier and the users expects write
+ * barrier semantics on wakeup functions. The following
+ * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
+ * and is paired with set_mb() in wait_woken().
+ */
+ smp_wmb(); /* C */
+ wait->flags |= WQ_FLAG_WOKEN;
+
+ return default_wake_function(wait, mode, sync, key);
+}
+EXPORT_SYMBOL(woken_wake_function);
+
int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
{
struct wait_bit_key *key = arg;