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Date: Sun, 18 Jan 2009 16:06:34 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: menage@...gle.com, miaox@...fujitsu.com, maxk@...lcomm.com,
linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] cgroup: introduce cgroup_queue_deferred_work()
Sometimes we need require a lock to prevent something,
but this lock cannot nest in cgroup_lock. So this work
should be moved out of cgroup_lock's critical region.
Using schedule_work() can move this work out of cgroup_lock's
critical region. But it's a overkill for move a work to
other process. And if we need flush_work() with cgroup_lock
held, schedule_work() can not work for flush_work() will
cause deadlock.
Another solution is that deferring the work, and processing
it after cgroup_lock released. This patch introduces
cgroup_queue_deferred_work() for queue a cgroup_deferred_work.
Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Max Krasnyansky <maxk@...lcomm.com>
Cc: Miao Xie <miaox@...fujitsu.com>
---
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e267e62..6d3e6dc 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -437,6 +437,19 @@ void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
int cgroup_scan_tasks(struct cgroup_scanner *scan);
int cgroup_attach_task(struct cgroup *, struct task_struct *);
+struct cgroup_deferred_work {
+ struct list_head list;
+ void (*func)(struct cgroup_deferred_work *);
+};
+
+#define CGROUP_DEFERRED_WORK(name, function) \
+ struct cgroup_deferred_work name = { \
+ .list = LIST_HEAD_INIT((name).list), \
+ .func = (function), \
+ };
+
+int cgroup_queue_deferred_work(struct cgroup_deferred_work *deferred_work);
+
#else /* !CONFIG_CGROUPS */
static inline int cgroup_init_early(void) { return 0; }
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c298310..75a352b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -540,6 +540,7 @@ void cgroup_lock(void)
mutex_lock(&cgroup_mutex);
}
+static void cgroup_flush_deferred_work_locked(void);
/**
* cgroup_unlock - release lock on cgroup changes
*
@@ -547,9 +548,80 @@ void cgroup_lock(void)
*/
void cgroup_unlock(void)
{
+ cgroup_flush_deferred_work_locked();
mutex_unlock(&cgroup_mutex);
}
+/* deferred_work_list is protected by cgroup_mutex */
+static LIST_HEAD(deferred_work_list);
+
+/* flush deferred works with cgroup_lock released */
+static void cgroup_flush_deferred_work_locked(void)
+{
+ static bool running_deferred_work;
+
+ if (likely(list_empty(&deferred_work_list)))
+ return;
+
+ /*
+ * Ensure it's not recursive and also
+ * ensure deferred works are run orderly.
+ */
+ if (running_deferred_work)
+ return;
+ running_deferred_work = true;
+
+ for ( ; ; ) {
+ struct cgroup_deferred_work *deferred_work;
+
+ /* dequeue the first work, and mark it dequeued */
+ deferred_work = list_first_entry(&deferred_work_list,
+ struct cgroup_deferred_work, list);
+ list_del_init(&deferred_work->list);
+
+ mutex_unlock(&cgroup_mutex);
+
+ /*
+ * cgroup_mutex is released. The callback function can use
+ * cgroup_lock()/cgroup_unlock(). This behavior is safe
+ * for running_deferred_work is set to 'true'.
+ */
+ deferred_work->func(deferred_work);
+
+ /*
+ * regain cgroup_mutex to access deferred_work_list
+ * and running_deferred_work.
+ */
+ mutex_lock(&cgroup_mutex);
+
+ if (list_empty(&deferred_work_list))
+ break;
+ }
+
+ running_deferred_work = false;
+}
+
+/**
+ * cgroup_queue_deferred_work - queue a deferred work
+ * @deferred_work: work to queue.
+ *
+ * Returns 0 if @deferred_work was already on the queue, non-zero otherwise.
+ *
+ * Must be called when cgroup_lock held.
+ * The deferred work will be run after cgroup_lock released.
+ */
+int cgroup_queue_deferred_work(struct cgroup_deferred_work *deferred_work)
+{
+ int ret = 0;
+
+ if (list_empty(&deferred_work->list)) {
+ list_add_tail(&deferred_work->list, &deferred_work_list);
+ ret = 1;
+ }
+
+ return ret;
+}
+
/*
* A couple of forward declarations required, due to cyclic reference loop:
* cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
--
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