workqueue: Replace pool->attach_mutex with global wq_pool_attach_mutex

To improve workqueue visibility, we want to be able to access
workqueue information from worker tasks.  The per-pool attach mutex
makes that difficult because there's no way of stabilizing task ->
worker pool association without knowing the pool first.

Worker attach/detach is a slow path and there's no need for different
pools to be able to perform them concurrently.  This patch replaces
the per-pool attach_mutex with global wq_pool_attach_mutex to prepare
for visibility improvement changes.

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ca7959b..91fe0a6 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -66,7 +66,7 @@ enum {
         * be executing on any CPU.  The pool behaves as an unbound one.
         *
         * Note that DISASSOCIATED should be flipped only while holding
-        * attach_mutex to avoid changing binding state while
+        * wq_pool_attach_mutex to avoid changing binding state while
         * worker_attach_to_pool() is in progress.
         */
        POOL_MANAGER_ACTIVE     = 1 << 0,       /* being managed */
@@ -123,7 +123,7 @@ enum {
  *    cpu or grabbing pool->lock is enough for read access.  If
  *    POOL_DISASSOCIATED is set, it's identical to L.
  *
- * A: pool->attach_mutex protected.
+ * A: wq_pool_attach_mutex protected.
  *
  * PL: wq_pool_mutex protected.
  *
@@ -166,7 +166,6 @@ struct worker_pool {
                                                /* L: hash of busy workers */
 
        struct worker           *manager;       /* L: purely informational */
-       struct mutex            attach_mutex;   /* attach/detach exclusion */
        struct list_head        workers;        /* A: attached workers */
        struct completion       *detach_completion; /* all workers detached */
 
@@ -297,6 +296,7 @@ static bool wq_numa_enabled;                /* unbound NUMA affinity enabled */
 static struct workqueue_attrs *wq_update_unbound_numa_attrs_buf;
 
 static DEFINE_MUTEX(wq_pool_mutex);    /* protects pools and workqueues list */
+static DEFINE_MUTEX(wq_pool_attach_mutex); /* protects worker attach/detach */
 static DEFINE_SPINLOCK(wq_mayday_lock);        /* protects wq->maydays list */
 static DECLARE_WAIT_QUEUE_HEAD(wq_manager_wait); /* wait for manager to go away */
 
@@ -399,14 +399,14 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
  * @worker: iteration cursor
  * @pool: worker_pool to iterate workers of
  *
- * This must be called with @pool->attach_mutex.
+ * This must be called with wq_pool_attach_mutex.
  *
  * The if/else clause exists only for the lockdep assertion and can be
  * ignored.
  */
 #define for_each_pool_worker(worker, pool)                             \
        list_for_each_entry((worker), &(pool)->workers, node)           \
-               if (({ lockdep_assert_held(&pool->attach_mutex); false; })) { } \
+               if (({ lockdep_assert_held(&wq_pool_attach_mutex); false; })) { } \
                else
 
 /**
@@ -1724,7 +1724,7 @@ static struct worker *alloc_worker(int node)
 static void worker_attach_to_pool(struct worker *worker,
                                   struct worker_pool *pool)
 {
-       mutex_lock(&pool->attach_mutex);
+       mutex_lock(&wq_pool_attach_mutex);
 
        /*
         * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
@@ -1733,16 +1733,16 @@ static void worker_attach_to_pool(struct worker *worker,
        set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
 
        /*
-        * The pool->attach_mutex ensures %POOL_DISASSOCIATED remains
-        * stable across this function.  See the comments above the
-        * flag definition for details.
+        * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
+        * stable across this function.  See the comments above the flag
+        * definition for details.
         */
        if (pool->flags & POOL_DISASSOCIATED)
                worker->flags |= WORKER_UNBOUND;
 
        list_add_tail(&worker->node, &pool->workers);
 
-       mutex_unlock(&pool->attach_mutex);
+       mutex_unlock(&wq_pool_attach_mutex);
 }
 
 /**
@@ -1759,11 +1759,11 @@ static void worker_detach_from_pool(struct worker *worker,
 {
        struct completion *detach_completion = NULL;
 
-       mutex_lock(&pool->attach_mutex);
+       mutex_lock(&wq_pool_attach_mutex);
        list_del(&worker->node);
        if (list_empty(&pool->workers))
                detach_completion = pool->detach_completion;
-       mutex_unlock(&pool->attach_mutex);
+       mutex_unlock(&wq_pool_attach_mutex);
 
        /* clear leftover flags without pool->lock after it is detached */
        worker->flags &= ~(WORKER_UNBOUND | WORKER_REBOUND);
@@ -3271,7 +3271,6 @@ static int init_worker_pool(struct worker_pool *pool)
 
        timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);
 
-       mutex_init(&pool->attach_mutex);
        INIT_LIST_HEAD(&pool->workers);
 
        ida_init(&pool->worker_ida);
@@ -3354,10 +3353,10 @@ static void put_unbound_pool(struct worker_pool *pool)
        WARN_ON(pool->nr_workers || pool->nr_idle);
        spin_unlock_irq(&pool->lock);
 
-       mutex_lock(&pool->attach_mutex);
+       mutex_lock(&wq_pool_attach_mutex);
        if (!list_empty(&pool->workers))
                pool->detach_completion = &detach_completion;
-       mutex_unlock(&pool->attach_mutex);
+       mutex_unlock(&wq_pool_attach_mutex);
 
        if (pool->detach_completion)
                wait_for_completion(pool->detach_completion);
@@ -4600,7 +4599,7 @@ static void unbind_workers(int cpu)
        struct worker *worker;
 
        for_each_cpu_worker_pool(pool, cpu) {
-               mutex_lock(&pool->attach_mutex);
+               mutex_lock(&wq_pool_attach_mutex);
                spin_lock_irq(&pool->lock);
 
                /*
@@ -4616,7 +4615,7 @@ static void unbind_workers(int cpu)
                pool->flags |= POOL_DISASSOCIATED;
 
                spin_unlock_irq(&pool->lock);
-               mutex_unlock(&pool->attach_mutex);
+               mutex_unlock(&wq_pool_attach_mutex);
 
                /*
                 * Call schedule() so that we cross rq->lock and thus can
@@ -4657,7 +4656,7 @@ static void rebind_workers(struct worker_pool *pool)
 {
        struct worker *worker;
 
-       lockdep_assert_held(&pool->attach_mutex);
+       lockdep_assert_held(&wq_pool_attach_mutex);
 
        /*
         * Restore CPU affinity of all workers.  As all idle workers should
@@ -4727,7 +4726,7 @@ static void restore_unbound_workers_cpumask(struct worker_pool *pool, int cpu)
        static cpumask_t cpumask;
        struct worker *worker;
 
-       lockdep_assert_held(&pool->attach_mutex);
+       lockdep_assert_held(&wq_pool_attach_mutex);
 
        /* is @cpu allowed for @pool? */
        if (!cpumask_test_cpu(cpu, pool->attrs->cpumask))
@@ -4762,14 +4761,14 @@ int workqueue_online_cpu(unsigned int cpu)
        mutex_lock(&wq_pool_mutex);
 
        for_each_pool(pool, pi) {
-               mutex_lock(&pool->attach_mutex);
+               mutex_lock(&wq_pool_attach_mutex);
 
                if (pool->cpu == cpu)
                        rebind_workers(pool);
                else if (pool->cpu < 0)
                        restore_unbound_workers_cpumask(pool, cpu);
 
-               mutex_unlock(&pool->attach_mutex);
+               mutex_unlock(&wq_pool_attach_mutex);
        }
 
        /* update NUMA affinity of unbound workqueues */