From: Peter Xu <peterx@redhat.com>
To: kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
peterx@redhat.com, "Radim Krčmář" <rkrcmar@redhat.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Peter Zijlstra" <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] sched/swait: allow swake_up() to return
Date: Thu, 9 Nov 2017 17:18:53 +0800 [thread overview]
Message-ID: <20171109091854.24367-2-peterx@redhat.com> (raw)
In-Reply-To: <20171109091854.24367-1-peterx@redhat.com>
Let swake_up() to return whether any of the waiters is waked up. One use
case of it would be:
if (swait_active(wq)) {
swake_up(wq);
// do something when waiter is waked up
waked_up++;
}
Logically it's possible that when reaching swake_up() the wait queue is
not active any more, and here doing something like waked_up++ would be
inaccurate. To correct it, we need an atomic version of it.
With this patch, we can simply re-write it into:
if (swake_up(wq)) {
// do something when waiter is waked up
waked_up++;
}
After all we are checking swait_active() inside swake_up() too.
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Peter Xu <peterx@redhat.com>
CC: linux-kernel@vger.kernel.org
Signed-off-by: Peter Xu <peterx@redhat.com>
---
include/linux/swait.h | 4 ++--
kernel/sched/swait.c | 21 ++++++++++++++++-----
2 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/include/linux/swait.h b/include/linux/swait.h
index c1f9c62a8a50..c55171280ac8 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -84,9 +84,9 @@ static inline int swait_active(struct swait_queue_head *q)
return !list_empty(&q->task_list);
}
-extern void swake_up(struct swait_queue_head *q);
+extern bool swake_up(struct swait_queue_head *q);
extern void swake_up_all(struct swait_queue_head *q);
-extern void swake_up_locked(struct swait_queue_head *q);
+extern bool swake_up_locked(struct swait_queue_head *q);
extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c
index 3d5610dcce11..31f8d677c690 100644
--- a/kernel/sched/swait.c
+++ b/kernel/sched/swait.c
@@ -16,29 +16,40 @@ EXPORT_SYMBOL(__init_swait_queue_head);
* If for some reason it would return 0, that means the previously waiting
* task is already running, so it will observe condition true (or has already).
*/
-void swake_up_locked(struct swait_queue_head *q)
+bool swake_up_locked(struct swait_queue_head *q)
{
struct swait_queue *curr;
if (list_empty(&q->task_list))
- return;
+ return false;
curr = list_first_entry(&q->task_list, typeof(*curr), task_list);
wake_up_process(curr->task);
list_del_init(&curr->task_list);
+ return true;
}
EXPORT_SYMBOL(swake_up_locked);
-void swake_up(struct swait_queue_head *q)
+/**
+ * swake_up - Wake up one process on the waiting list
+ * @q: the waitqueue to wake up
+ *
+ * Returns true if some process is waked up, otherwise false if there
+ * is no waiter to wake up.
+ */
+bool swake_up(struct swait_queue_head *q)
{
+ bool ret;
unsigned long flags;
if (!swait_active(q))
- return;
+ return false;
raw_spin_lock_irqsave(&q->lock, flags);
- swake_up_locked(q);
+ ret = swake_up_locked(q);
raw_spin_unlock_irqrestore(&q->lock, flags);
+
+ return ret;
}
EXPORT_SYMBOL(swake_up);
--
2.13.6
next parent reply other threads:[~2017-11-09 9:19 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20171109091854.24367-1-peterx@redhat.com>
2017-11-09 9:18 ` Peter Xu [this message]
2017-11-09 10:06 ` [PATCH 1/2] sched/swait: allow swake_up() to return Paolo Bonzini
2017-11-10 7:12 ` Peter Xu
2017-11-09 10:23 ` Peter Zijlstra
2017-11-10 7:10 ` Peter Xu
2017-11-10 8:05 ` Peter Zijlstra
2017-11-13 3:33 ` Peter Xu
2017-11-13 5:19 ` Peter Xu
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