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workqueue: make the workqueues list RCU walkable

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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>
This commit is contained in:
Tejun Heo 2015-03-09 09:22:28 -04:00
parent 8603e1b300
commit e2dca7adff
1 changed files with 31 additions and 16 deletions
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47
kernel/workqueue.c
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@ -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