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workqueue: separate out pool and workqueue locking into wq_mutex

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Currently, workqueue_lock protects most shared workqueue resources -
the pools, workqueues, pool_workqueues, draining, ID assignments,
mayday handling and so on.  The coverage has grown organically and
there is no identified bottleneck coming from workqueue_lock, but it
has grown a bit too much and scheduled rebinding changes need the
pools and workqueues to be protected by a mutex instead of a spinlock.

This patch breaks out pool and workqueue synchronization from
workqueue_lock into a new mutex - wq_mutex.  The followings are
protected by wq_mutex.

* worker_pool_idr and unbound_pool_hash
* pool->refcnt
* workqueues list
* workqueue->flags, ->nr_drainers

Most changes are mostly straight-forward.  workqueue_lock is replaced
with wq_mutex where applicable and workqueue_lock lock/unlocks are
added where wq_mutex conversion leaves data structures not protected
by wq_mutex without locking.  irq / preemption flippings were added
where the conversion affects them.  Things worth noting are

* New WQ and WR locking lables added along with
  assert_rcu_or_wq_mutex().

* worker_pool_assign_id() now expects to be called under wq_mutex.

* create_mutex is removed from get_unbound_pool().  It now just holds
  wq_mutex.

This patch shouldn't introduce any visible behavior changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2013-03-13 19:47:40 -07:00
parent 7d19c5ce66
commit 5bcab3355a
1 changed files with 77 additions and 69 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

146
kernel/workqueue.c
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@ -119,9 +119,11 @@ enum {
*
* F: wq->flush_mutex protected.
*
* W: workqueue_lock protected.
* WQ: wq_mutex protected.
*
* R: workqueue_lock protected for writes. Sched-RCU protected for reads.
* WR: wq_mutex protected for writes. Sched-RCU protected for reads.
*
* W: workqueue_lock protected.
*
* FR: wq->flush_mutex and workqueue_lock protected for writes. Sched-RCU
* protected for reads.
@ -155,8 +157,8 @@ struct worker_pool {
struct ida worker_ida; /* L: for worker IDs */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* W: unbound_pool_hash node */
int refcnt; /* W: refcnt for unbound pools */
struct hlist_node hash_node; /* WQ: unbound_pool_hash node */
int refcnt; /* WQ: refcnt for unbound pools */
/*
* The current concurrency level. As it's likely to be accessed
@ -218,10 +220,10 @@ struct wq_device;
* the appropriate worker_pool through its pool_workqueues.
*/
struct workqueue_struct {
unsigned int flags; /* W: WQ_* flags */
unsigned int flags; /* WQ: WQ_* flags */
struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwq's */
struct list_head pwqs; /* FR: all pwqs of this wq */
struct list_head list; /* W: list of all workqueues */
struct list_head list; /* WQ: list of all workqueues */
struct mutex flush_mutex; /* protects wq flushing */
int work_color; /* F: current work color */
@ -234,7 +236,7 @@ struct workqueue_struct {
struct list_head maydays; /* W: pwqs requesting rescue */
struct worker *rescuer; /* I: rescue worker */
int nr_drainers; /* W: drain in progress */
int nr_drainers; /* WQ: drain in progress */
int saved_max_active; /* W: saved pwq max_active */
#ifdef CONFIG_SYSFS
@ -248,22 +250,19 @@ struct workqueue_struct {
static struct kmem_cache *pwq_cache;
/* Serializes the accesses to the list of workqueues. */
static DEFINE_MUTEX(wq_mutex); /* protects workqueues and pools */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static bool workqueue_freezing; /* W: have wqs started freezing? */
static LIST_HEAD(workqueues); /* WQ: list of all workqueues */
static bool workqueue_freezing; /* WQ: have wqs started freezing? */
/* the per-cpu worker pools */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
cpu_worker_pools);
/*
* R: idr of all pools. Modifications are protected by workqueue_lock.
* Read accesses are protected by sched-RCU protected.
*/
static DEFINE_IDR(worker_pool_idr);
static DEFINE_IDR(worker_pool_idr); /* WR: idr of all pools */
/* W: hash of all unbound pools keyed by pool->attrs */
/* WQ: hash of all unbound pools keyed by pool->attrs */
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
/* I: attributes used when instantiating standard unbound pools on demand */
@ -287,6 +286,11 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>
#define assert_rcu_or_wq_mutex() \
rcu_lockdep_assert(rcu_read_lock_sched_held() || \
lockdep_is_held(&wq_mutex), \
"sched RCU or wq_mutex should be held")
#define assert_rcu_or_wq_lock() \
rcu_lockdep_assert(rcu_read_lock_sched_held() || \
lockdep_is_held(&workqueue_lock), \
@ -305,16 +309,16 @@ static void copy_workqueue_attrs(struct workqueue_attrs *to,
* @pool: iteration cursor
* @pi: integer used for iteration
*
* This must be called either with workqueue_lock held or sched RCU read
* locked. If the pool needs to be used beyond the locking in effect, the
* caller is responsible for guaranteeing that the pool stays online.
* This must be called either with wq_mutex held or sched RCU read locked.
* If the pool needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pool stays online.
*
* The if/else clause exists only for the lockdep assertion and can be
* ignored.
*/
#define for_each_pool(pool, pi) \
idr_for_each_entry(&worker_pool_idr, pool, pi) \
if (({ assert_rcu_or_wq_lock(); false; })) { } \
if (({ assert_rcu_or_wq_mutex(); false; })) { } \
else
/**
@ -455,13 +459,12 @@ static int worker_pool_assign_id(struct worker_pool *pool)
{
int ret;
lockdep_assert_held(&wq_mutex);
do {
if (!idr_pre_get(&worker_pool_idr, GFP_KERNEL))
return -ENOMEM;
spin_lock_irq(&workqueue_lock);
ret = idr_get_new(&worker_pool_idr, pool, &pool->id);
spin_unlock_irq(&workqueue_lock);
} while (ret == -EAGAIN);
return ret;
@ -574,9 +577,9 @@ static struct pool_workqueue *get_work_pwq(struct work_struct *work)
*
* Return the worker_pool @work was last associated with. %NULL if none.
*
* Pools are created and destroyed under workqueue_lock, and allows read
* access under sched-RCU read lock. As such, this function should be
* called under workqueue_lock or with preemption disabled.
* Pools are created and destroyed under wq_mutex, and allows read access
* under sched-RCU read lock. As such, this function should be called
* under wq_mutex or with preemption disabled.
*
* All fields of the returned pool are accessible as long as the above
* mentioned locking is in effect. If the returned pool needs to be used
@ -588,7 +591,7 @@ static struct worker_pool *get_work_pool(struct work_struct *work)
unsigned long data = atomic_long_read(&work->data);
int pool_id;
assert_rcu_or_wq_lock();
assert_rcu_or_wq_mutex();
if (data & WORK_STRUCT_PWQ)
return ((struct pool_workqueue *)
@ -2768,10 +2771,10 @@ void drain_workqueue(struct workqueue_struct *wq)
* hotter than drain_workqueue() and already looks at @wq->flags.
* Use __WQ_DRAINING so that queue doesn't have to check nr_drainers.
*/
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
if (!wq->nr_drainers++)
wq->flags |= __WQ_DRAINING;
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
reflush:
flush_workqueue(wq);
@ -2796,12 +2799,12 @@ reflush:
goto reflush;
}
spin_lock(&workqueue_lock);
local_irq_enable();
mutex_lock(&wq_mutex);
if (!--wq->nr_drainers)
wq->flags &= ~__WQ_DRAINING;
spin_unlock(&workqueue_lock);
local_irq_enable();
mutex_unlock(&wq_mutex);
}
EXPORT_SYMBOL_GPL(drain_workqueue);
@ -3514,16 +3517,16 @@ static void put_unbound_pool(struct worker_pool *pool)
{
struct worker *worker;
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
if (--pool->refcnt) {
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
return;
}
/* sanity checks */
if (WARN_ON(!(pool->flags & POOL_DISASSOCIATED)) ||
WARN_ON(!list_empty(&pool->worklist))) {
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
return;
}
@ -3532,7 +3535,7 @@ static void put_unbound_pool(struct worker_pool *pool)
idr_remove(&worker_pool_idr, pool->id);
hash_del(&pool->hash_node);
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
/*
* Become the manager and destroy all workers. Grabbing
@ -3570,21 +3573,18 @@ static void put_unbound_pool(struct worker_pool *pool)
*/
static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
{
static DEFINE_MUTEX(create_mutex);
u32 hash = wqattrs_hash(attrs);
struct worker_pool *pool;
mutex_lock(&create_mutex);
mutex_lock(&wq_mutex);
/* do we already have a matching pool? */
spin_lock_irq(&workqueue_lock);
hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
if (wqattrs_equal(pool->attrs, attrs)) {
pool->refcnt++;
goto out_unlock;
}
}
spin_unlock_irq(&workqueue_lock);
/* nope, create a new one */
pool = kzalloc(sizeof(*pool), GFP_KERNEL);
@ -3602,14 +3602,12 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
goto fail;
/* install */
spin_lock_irq(&workqueue_lock);
hash_add(unbound_pool_hash, &pool->hash_node, hash);
out_unlock:
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&create_mutex);
mutex_unlock(&wq_mutex);
return pool;
fail:
mutex_unlock(&create_mutex);
mutex_unlock(&wq_mutex);
if (pool)
put_unbound_pool(pool);
return NULL;
@ -3883,18 +3881,19 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
goto err_destroy;
/*
* workqueue_lock protects global freeze state and workqueues list.
* Grab it, adjust max_active and add the new workqueue to
* workqueues list.
* wq_mutex protects global freeze state and workqueues list. Grab
* it, adjust max_active and add the new @wq to workqueues list.
*/
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
spin_lock_irq(&workqueue_lock);
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
spin_unlock_irq(&workqueue_lock);
list_add(&wq->list, &workqueues);
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
return wq;
@ -3920,9 +3919,8 @@ void destroy_workqueue(struct workqueue_struct *wq)
/* drain it before proceeding with destruction */
drain_workqueue(wq);
spin_lock_irq(&workqueue_lock);
/* sanity checks */
spin_lock_irq(&workqueue_lock);
for_each_pwq(pwq, wq) {
int i;
@ -3940,14 +3938,15 @@ void destroy_workqueue(struct workqueue_struct *wq)
return;
}
}
spin_unlock_irq(&workqueue_lock);
/*
* wq list is used to freeze wq, remove from list after
* flushing is complete in case freeze races us.
*/
mutex_lock(&wq_mutex);
list_del_init(&wq->list);
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
workqueue_sysfs_unregister(wq);
@ -4267,7 +4266,7 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
* pool->worklist.
*
* CONTEXT:
* Grabs and releases workqueue_lock and pool->lock's.
* Grabs and releases wq_mutex, workqueue_lock and pool->lock's.
*/
void freeze_workqueues_begin(void)
{
@ -4276,26 +4275,28 @@ void freeze_workqueues_begin(void)
struct pool_workqueue *pwq;
int pi;
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
WARN_ON_ONCE(workqueue_freezing);
workqueue_freezing = true;
/* set FREEZING */
for_each_pool(pool, pi) {
spin_lock(&pool->lock);
spin_lock_irq(&pool->lock);
WARN_ON_ONCE(pool->flags & POOL_FREEZING);
pool->flags |= POOL_FREEZING;
spin_unlock(&pool->lock);
spin_unlock_irq(&pool->lock);
}
/* suppress further executions by setting max_active to zero */
spin_lock_irq(&workqueue_lock);
list_for_each_entry(wq, &workqueues, list) {
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
}
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
}
/**
@ -4305,7 +4306,7 @@ void freeze_workqueues_begin(void)
* between freeze_workqueues_begin() and thaw_workqueues().
*
* CONTEXT:
* Grabs and releases workqueue_lock.
* Grabs and releases wq_mutex.
*
* RETURNS:
* %true if some freezable workqueues are still busy. %false if freezing
@ -4317,7 +4318,7 @@ bool freeze_workqueues_busy(void)
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
WARN_ON_ONCE(!workqueue_freezing);
@ -4328,16 +4329,19 @@ bool freeze_workqueues_busy(void)
* nr_active is monotonically decreasing. It's safe
* to peek without lock.
*/
preempt_disable();
for_each_pwq(pwq, wq) {
WARN_ON_ONCE(pwq->nr_active < 0);
if (pwq->nr_active) {
busy = true;
preempt_enable();
goto out_unlock;
}
}
preempt_enable();
}
out_unlock:
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
return busy;
}
@ -4348,7 +4352,7 @@ out_unlock:
* frozen works are transferred to their respective pool worklists.
*
* CONTEXT:
* Grabs and releases workqueue_lock and pool->lock's.
* Grabs and releases wq_mutex, workqueue_lock and pool->lock's.
*/
void thaw_workqueues(void)
{
@ -4357,35 +4361,37 @@ void thaw_workqueues(void)
struct worker_pool *pool;
int pi;
spin_lock_irq(&workqueue_lock);
mutex_lock(&wq_mutex);
if (!workqueue_freezing)
goto out_unlock;
/* clear FREEZING */
for_each_pool(pool, pi) {
spin_lock(&pool->lock);
spin_lock_irq(&pool->lock);
WARN_ON_ONCE(!(pool->flags & POOL_FREEZING));
pool->flags &= ~POOL_FREEZING;
spin_unlock(&pool->lock);
spin_unlock_irq(&pool->lock);
}
/* restore max_active and repopulate worklist */
spin_lock_irq(&workqueue_lock);
list_for_each_entry(wq, &workqueues, list) {
for_each_pwq(pwq, wq)
pwq_adjust_max_active(pwq);
}
spin_unlock_irq(&workqueue_lock);
/* kick workers */
for_each_pool(pool, pi) {
spin_lock(&pool->lock);
spin_lock_irq(&pool->lock);
wake_up_worker(pool);
spin_unlock(&pool->lock);
spin_unlock_irq(&pool->lock);
}
workqueue_freezing = false;
out_unlock:
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&wq_mutex);
}
#endif /* CONFIG_FREEZER */
@ -4417,7 +4423,9 @@ static int __init init_workqueues(void)
pool->attrs->nice = std_nice[i++];
/* alloc pool ID */
mutex_lock(&wq_mutex);
BUG_ON(worker_pool_assign_id(pool));
mutex_unlock(&wq_mutex);
}
}