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authorTejun Heo <tj@kernel.org>2015-03-09 09:22:28 -0400
committerTejun Heo <tj@kernel.org>2015-03-09 09:22:28 -0400
commite2dca7adff8f3fae0ab250a6362798550b3c79ee (patch)
tree3b86a4dfbc600872645c856d3d45b8b3af4d3cff /kernel/workqueue.c
parent8603e1b30027f943cc9c1eef2b291d42c3347af1 (diff)
downloadlinux-sh-e2dca7adff8f3fae0ab250a6362798550b3c79ee.tar.gz
workqueue: make the workqueues list RCU walkable
The workqueues list is protected by wq_pool_mutex and a workqueue and its subordinate data structures are freed directly on destruction. We want to add the ability dump workqueues from a sysrq callback which requires walking all workqueues without grabbing wq_pool_mutex. This patch makes freeing of workqueues RCU protected and makes the workqueues list walkable while holding RCU read lock. Note that pool_workqueues and pools are already sched-RCU protected. For consistency, workqueues are also protected with sched-RCU. While at it, reverse the workqueues list so that a workqueue which is created earlier comes before. The order of the list isn't significant functionally but this makes the planned sysrq dump list system workqueues first. Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c47
1 files changed, 31 insertions, 16 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 41ff75b478c6..6b9b0dc3dea5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -230,7 +230,7 @@ struct wq_device;
*/
struct workqueue_struct {
struct list_head pwqs; /* WR: all pwqs of this wq */
- struct list_head list; /* PL: list of all workqueues */
+ struct list_head list; /* PR: list of all workqueues */
struct mutex mutex; /* protects this wq */
int work_color; /* WQ: current work color */
@@ -257,6 +257,13 @@ struct workqueue_struct {
#endif
char name[WQ_NAME_LEN]; /* I: workqueue name */
+ /*
+ * Destruction of workqueue_struct is sched-RCU protected to allow
+ * walking the workqueues list without grabbing wq_pool_mutex.
+ * This is used to dump all workqueues from sysrq.
+ */
+ struct rcu_head rcu;
+
/* hot fields used during command issue, aligned to cacheline */
unsigned int flags ____cacheline_aligned; /* WQ: WQ_* flags */
struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwqs */
@@ -288,7 +295,7 @@ static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
static DEFINE_MUTEX(wq_pool_mutex); /* protects pools and workqueues list */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
-static LIST_HEAD(workqueues); /* PL: list of all workqueues */
+static LIST_HEAD(workqueues); /* PR: list of all workqueues */
static bool workqueue_freezing; /* PL: have wqs started freezing? */
/* the per-cpu worker pools */
@@ -3424,6 +3431,20 @@ static int init_worker_pool(struct worker_pool *pool)
return 0;
}
+static void rcu_free_wq(struct rcu_head *rcu)
+{
+ struct workqueue_struct *wq =
+ container_of(rcu, struct workqueue_struct, rcu);
+
+ if (!(wq->flags & WQ_UNBOUND))
+ free_percpu(wq->cpu_pwqs);
+ else
+ free_workqueue_attrs(wq->unbound_attrs);
+
+ kfree(wq->rescuer);
+ kfree(wq);
+}
+
static void rcu_free_pool(struct rcu_head *rcu)
{
struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
@@ -3601,12 +3622,10 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
/*
* If we're the last pwq going away, @wq is already dead and no one
- * is gonna access it anymore. Free it.
+ * is gonna access it anymore. Schedule RCU free.
*/
- if (is_last) {
- free_workqueue_attrs(wq->unbound_attrs);
- kfree(wq);
- }
+ if (is_last)
+ call_rcu_sched(&wq->rcu, rcu_free_wq);
}
/**
@@ -4143,7 +4162,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
pwq_adjust_max_active(pwq);
mutex_unlock(&wq->mutex);
- list_add(&wq->list, &workqueues);
+ list_add_tail_rcu(&wq->list, &workqueues);
mutex_unlock(&wq_pool_mutex);
@@ -4199,24 +4218,20 @@ void destroy_workqueue(struct workqueue_struct *wq)
* flushing is complete in case freeze races us.
*/
mutex_lock(&wq_pool_mutex);
- list_del_init(&wq->list);
+ list_del_rcu(&wq->list);
mutex_unlock(&wq_pool_mutex);
workqueue_sysfs_unregister(wq);
- if (wq->rescuer) {
+ if (wq->rescuer)
kthread_stop(wq->rescuer->task);
- kfree(wq->rescuer);
- wq->rescuer = NULL;
- }
if (!(wq->flags & WQ_UNBOUND)) {
/*
* The base ref is never dropped on per-cpu pwqs. Directly
- * free the pwqs and wq.
+ * schedule RCU free.
*/
- free_percpu(wq->cpu_pwqs);
- kfree(wq);
+ call_rcu_sched(&wq->rcu, rcu_free_wq);
} else {
/*
* We're the sole accessor of @wq at this point. Directly