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workqueue: wq_pool_mutex protects the attrs-installation 

Current wq_pool_mutex doesn't proctect the attrs-installation, it results
that ->unbound_attrs, ->numa_pwq_tbl[] and ->dfl_pwq can only be accessed
under wq->mutex and causes some inconveniences. Example, wq_update_unbound_numa()
has to acquire wq->mutex before fetching the wq->unbound_attrs->no_numa
and the old_pwq.

attrs-installation is a short operation, so this change will no cause any
latency for other operations which also acquire the wq_pool_mutex.

The only unprotected attrs-installation code is in apply_workqueue_attrs(),
so this patch touches code less than comments.

It is also a preparation patch for next several patches which read
wq->unbound_attrs, wq->numa_pwq_tbl[] and wq->dfl_pwq with
only wq_pool_mutex held.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2015-05-12 20:32:29 +08:00 committed by Tejun Heo
parent b749b1b673
commit 5b95e1af8d
1 changed files with 20 additions and 7 deletions
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27
kernel/workqueue.c
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@ -127,6 +127,11 @@ enum {
*
* PR: wq_pool_mutex protected for writes. Sched-RCU protected for reads.
*
* PW: wq_pool_mutex and wq->mutex protected for writes. Either for reads.
*
* PWR: wq_pool_mutex and wq->mutex protected for writes. Either or
* sched-RCU for reads.
*
* WQ: wq->mutex protected.
*
* WR: wq->mutex protected for writes. Sched-RCU protected for reads.
@ -247,8 +252,8 @@ struct workqueue_struct {
int nr_drainers; /* WQ: drain in progress */
int saved_max_active; /* WQ: saved pwq max_active */
struct workqueue_attrs *unbound_attrs; /* WQ: only for unbound wqs */
struct pool_workqueue *dfl_pwq; /* WQ: only for unbound wqs */
struct workqueue_attrs *unbound_attrs; /* PW: only for unbound wqs */
struct pool_workqueue *dfl_pwq; /* PW: only for unbound wqs */
#ifdef CONFIG_SYSFS
struct wq_device *wq_dev; /* I: for sysfs interface */
@ -268,7 +273,7 @@ struct workqueue_struct {
/* 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 */
struct pool_workqueue __rcu *numa_pwq_tbl[]; /* FR: unbound pwqs indexed by node */
struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
};
static struct kmem_cache *pwq_cache;
@ -349,6 +354,12 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
lockdep_is_held(&wq->mutex), \
"sched RCU or wq->mutex should be held")
#define assert_rcu_or_wq_mutex_or_pool_mutex(wq) \
rcu_lockdep_assert(rcu_read_lock_sched_held() || \
lockdep_is_held(&wq->mutex) || \
lockdep_is_held(&wq_pool_mutex), \
"sched RCU, wq->mutex or wq_pool_mutex should be held")
#define for_each_cpu_worker_pool(pool, cpu) \
for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0]; \
(pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
@ -553,7 +564,8 @@ static int worker_pool_assign_id(struct worker_pool *pool)
* @wq: the target workqueue
* @node: the node ID
*
* This must be called either with pwq_lock held or sched RCU read locked.
* This must be called with any of wq_pool_mutex, wq->mutex or sched RCU
* read locked.
* If the pwq needs to be used beyond the locking in effect, the caller is
* responsible for guaranteeing that the pwq stays online.
*
@ -562,7 +574,7 @@ static int worker_pool_assign_id(struct worker_pool *pool)
static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
int node)
{
assert_rcu_or_wq_mutex(wq);
assert_rcu_or_wq_mutex_or_pool_mutex(wq);
return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}
@ -3479,6 +3491,7 @@ static struct pool_workqueue *numa_pwq_tbl_install(struct workqueue_struct *wq,
{
struct pool_workqueue *old_pwq;
lockdep_assert_held(&wq_pool_mutex);
lockdep_assert_held(&wq->mutex);
/* link_pwq() can handle duplicate calls */
@ -3644,10 +3657,9 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
* pwqs accordingly.
*/
get_online_cpus();
mutex_lock(&wq_pool_mutex);
ctx = apply_wqattrs_prepare(wq, attrs);
mutex_unlock(&wq_pool_mutex);
/* the ctx has been prepared successfully, let's commit it */
if (ctx) {
@ -3655,6 +3667,7 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
ret = 0;
}
mutex_unlock(&wq_pool_mutex);
put_online_cpus();
apply_wqattrs_cleanup(ctx);