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workqueue: Make per-cpu pool_workqueues allocated and released like unbound ones

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Currently, all per-cpu pwq's (pool_workqueue's) are allocated directly
through a per-cpu allocation and thus, unlike unbound workqueues, not
reference counted. This difference in lifetime management between the two
types is a bit confusing.

Unbound workqueues are currently accessed through wq->numa_pwq_tbl[] which
isn't suitiable for the planned CPU locality related improvements. The plan
is to unify pwq handling across per-cpu and unbound workqueues so that
they're always accessed through wq->cpu_pwq.

In preparation, this patch makes per-cpu pwq's to be allocated, reference
counted and released the same way as unbound pwq's. wq->cpu_pwq now holds
pointers to pwq's instead of containing them directly.

pwq_unbound_release_workfn() is renamed to pwq_release_workfn() as it's now
also used for per-cpu work items.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2023-08-07 15:57:23 -10:00
parent 967b494e2f
commit 687a9aa56f
1 changed files with 40 additions and 34 deletions
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74
kernel/workqueue.c
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@ -258,11 +258,11 @@ struct pool_workqueue {
/*
* Release of unbound pwq is punted to a kthread_worker. See put_pwq()
* and pwq_unbound_release_workfn() for details. pool_workqueue itself
* is also RCU protected so that the first pwq can be determined without
* and pwq_release_workfn() for details. pool_workqueue itself is also
* RCU protected so that the first pwq can be determined without
* grabbing wq->mutex.
*/
struct kthread_work unbound_release_work;
struct kthread_work release_work;
struct rcu_head rcu;
} __aligned(1 << WORK_STRUCT_FLAG_BITS);
@ -321,7 +321,7 @@ 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_pwq; /* I: per-cpu pwqs */
struct pool_workqueue __percpu **cpu_pwq; /* I: per-cpu pwqs */
struct pool_workqueue __rcu *numa_pwq_tbl[]; /* PWR: unbound pwqs indexed by node */
};
@ -1370,13 +1370,11 @@ static void put_pwq(struct pool_workqueue *pwq)
lockdep_assert_held(&pwq->pool->lock);
if (likely(--pwq->refcnt))
return;
if (WARN_ON_ONCE(!(pwq->wq->flags & WQ_UNBOUND)))
return;
/*
* @pwq can't be released under pool->lock, bounce to a dedicated
* kthread_worker to avoid A-A deadlocks.
*/
kthread_queue_work(pwq_release_worker, &pwq->unbound_release_work);
kthread_queue_work(pwq_release_worker, &pwq->release_work);
}
/**
@ -1685,7 +1683,7 @@ retry:
} else {
if (req_cpu == WORK_CPU_UNBOUND)
cpu = raw_smp_processor_id();
pwq = per_cpu_ptr(wq->cpu_pwq, cpu);
pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
}
pool = pwq->pool;
@ -4004,31 +4002,30 @@ static void rcu_free_pwq(struct rcu_head *rcu)
* Scheduled on pwq_release_worker by put_pwq() when an unbound pwq hits zero
* refcnt and needs to be destroyed.
*/
static void pwq_unbound_release_workfn(struct kthread_work *work)
static void pwq_release_workfn(struct kthread_work *work)
{
struct pool_workqueue *pwq = container_of(work, struct pool_workqueue,
unbound_release_work);
release_work);
struct workqueue_struct *wq = pwq->wq;
struct worker_pool *pool = pwq->pool;
bool is_last = false;
/*
* when @pwq is not linked, it doesn't hold any reference to the
* When @pwq is not linked, it doesn't hold any reference to the
* @wq, and @wq is invalid to access.
*/
if (!list_empty(&pwq->pwqs_node)) {
if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
return;
mutex_lock(&wq->mutex);
list_del_rcu(&pwq->pwqs_node);
is_last = list_empty(&wq->pwqs);
mutex_unlock(&wq->mutex);
}
mutex_lock(&wq_pool_mutex);
put_unbound_pool(pool);
mutex_unlock(&wq_pool_mutex);
if (wq->flags & WQ_UNBOUND) {
mutex_lock(&wq_pool_mutex);
put_unbound_pool(pool);
mutex_unlock(&wq_pool_mutex);
}
call_rcu(&pwq->rcu, rcu_free_pwq);
@ -4112,8 +4109,7 @@ static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
INIT_LIST_HEAD(&pwq->inactive_works);
INIT_LIST_HEAD(&pwq->pwqs_node);
INIT_LIST_HEAD(&pwq->mayday_node);
kthread_init_work(&pwq->unbound_release_work,
pwq_unbound_release_workfn);
kthread_init_work(&pwq->release_work, pwq_release_workfn);
}
/* sync @pwq with the current state of its associated wq and link it */
@ -4514,20 +4510,25 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
int cpu, ret;
if (!(wq->flags & WQ_UNBOUND)) {
wq->cpu_pwq = alloc_percpu(struct pool_workqueue);
wq->cpu_pwq = alloc_percpu(struct pool_workqueue *);
if (!wq->cpu_pwq)
return -ENOMEM;
goto enomem;
for_each_possible_cpu(cpu) {
struct pool_workqueue *pwq =
struct pool_workqueue **pwq_p =
per_cpu_ptr(wq->cpu_pwq, cpu);
struct worker_pool *cpu_pools =
per_cpu(cpu_worker_pools, cpu);
struct worker_pool *pool =
&(per_cpu_ptr(cpu_worker_pools, cpu)[highpri]);
init_pwq(pwq, wq, &cpu_pools[highpri]);
*pwq_p = kmem_cache_alloc_node(pwq_cache, GFP_KERNEL,
pool->node);
if (!*pwq_p)
goto enomem;
init_pwq(*pwq_p, wq, pool);
mutex_lock(&wq->mutex);
link_pwq(pwq);
link_pwq(*pwq_p);
mutex_unlock(&wq->mutex);
}
return 0;
@ -4546,6 +4547,15 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
cpus_read_unlock();
return ret;
enomem:
if (wq->cpu_pwq) {
for_each_possible_cpu(cpu)
kfree(*per_cpu_ptr(wq->cpu_pwq, cpu));
free_percpu(wq->cpu_pwq);
wq->cpu_pwq = NULL;
}
return -ENOMEM;
}
static int wq_clamp_max_active(int max_active, unsigned int flags,
@ -4719,7 +4729,7 @@ static bool pwq_busy(struct pool_workqueue *pwq)
void destroy_workqueue(struct workqueue_struct *wq)
{
struct pool_workqueue *pwq;
int node;
int cpu, node;
/*
* Remove it from sysfs first so that sanity check failure doesn't
@ -4779,12 +4789,8 @@ void destroy_workqueue(struct workqueue_struct *wq)
mutex_unlock(&wq_pool_mutex);
if (!(wq->flags & WQ_UNBOUND)) {
wq_unregister_lockdep(wq);
/*
* The base ref is never dropped on per-cpu pwqs. Directly
* schedule RCU free.
*/
call_rcu(&wq->rcu, rcu_free_wq);
for_each_possible_cpu(cpu)
put_pwq_unlocked(*per_cpu_ptr(wq->cpu_pwq, cpu));
} else {
/*
* We're the sole accessor of @wq at this point. Directly
@ -4901,7 +4907,7 @@ bool workqueue_congested(int cpu, struct workqueue_struct *wq)
cpu = smp_processor_id();
if (!(wq->flags & WQ_UNBOUND))
pwq = per_cpu_ptr(wq->cpu_pwq, cpu);
pwq = *per_cpu_ptr(wq->cpu_pwq, cpu);
else
pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));