workqueue: Use normal rcu
authorThomas Gleixner <tglx@linutronix.de>
Wed, 13 Mar 2019 16:55:47 +0000 (17:55 +0100)
committerTejun Heo <tj@kernel.org>
Mon, 8 Apr 2019 19:37:43 +0000 (12:37 -0700)
There is no need for sched_rcu. The undocumented reason why sched_rcu
is used is to avoid a few explicit rcu_read_lock()/unlock() pairs by
the fact that sched_rcu reader side critical sections are also protected
by preempt or irq disabled regions.

Replace rcu_read_lock_sched with rcu_read_lock and acquire the RCU lock
where it is not yet explicit acquired. Replace local_irq_disable() with
rcu_read_lock(). Update asserts.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: mangle changelog a little]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
kernel/workqueue.c

index 21721fa..37a3288 100644 (file)
@@ -127,16 +127,16 @@ enum {
  *
  * PL: wq_pool_mutex protected.
  *
- * PR: wq_pool_mutex protected for writes.  Sched-RCU protected for reads.
+ * PR: wq_pool_mutex protected for writes.  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.
+ *      RCU for reads.
  *
  * WQ: wq->mutex protected.
  *
- * WR: wq->mutex protected for writes.  Sched-RCU protected for reads.
+ * WR: wq->mutex protected for writes.  RCU protected for reads.
  *
  * MD: wq_mayday_lock protected.
  */
@@ -183,7 +183,7 @@ struct worker_pool {
        atomic_t                nr_running ____cacheline_aligned_in_smp;
 
        /*
-        * Destruction of pool is sched-RCU protected to allow dereferences
+        * Destruction of pool is RCU protected to allow dereferences
         * from get_work_pool().
         */
        struct rcu_head         rcu;
@@ -212,7 +212,7 @@ struct pool_workqueue {
        /*
         * Release of unbound pwq is punted to system_wq.  See put_pwq()
         * and pwq_unbound_release_workfn() for details.  pool_workqueue
-        * itself is also sched-RCU protected so that the first pwq can be
+        * itself is also RCU protected so that the first pwq can be
         * determined without grabbing wq->mutex.
         */
        struct work_struct      unbound_release_work;
@@ -266,8 +266,8 @@ struct workqueue_struct {
        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.
+        * Destruction of workqueue_struct is 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;
@@ -359,20 +359,20 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 #include <trace/events/workqueue.h>
 
 #define assert_rcu_or_pool_mutex()                                     \
-       RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&                 \
+       RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq_pool_mutex),              \
-                        "sched RCU or wq_pool_mutex should be held")
+                        "RCU or wq_pool_mutex should be held")
 
 #define assert_rcu_or_wq_mutex(wq)                                     \
-       RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&                 \
+       RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq->mutex),                  \
-                        "sched RCU or wq->mutex should be held")
+                        "RCU or wq->mutex should be held")
 
 #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)                       \
-       RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held() &&                 \
+       RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
                         !lockdep_is_held(&wq->mutex) &&                \
                         !lockdep_is_held(&wq_pool_mutex),              \
-                        "sched RCU, wq->mutex or wq_pool_mutex should be held")
+                        "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];               \
@@ -384,7 +384,7 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
  * @pool: iteration cursor
  * @pi: integer used for iteration
  *
- * This must be called either with wq_pool_mutex held or sched RCU read
+ * This must be called either with wq_pool_mutex held or 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.
  *
@@ -416,7 +416,7 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
  * @pwq: iteration cursor
  * @wq: the target workqueue
  *
- * This must be called either with wq->mutex held or sched RCU read locked.
+ * This must be called either with wq->mutex held or 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.
  *
@@ -552,7 +552,7 @@ static int worker_pool_assign_id(struct worker_pool *pool)
  * @wq: the target workqueue
  * @node: the node ID
  *
- * This must be called with any of wq_pool_mutex, wq->mutex or sched RCU
+ * This must be called with any of wq_pool_mutex, wq->mutex or 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.
@@ -696,8 +696,8 @@ static struct pool_workqueue *get_work_pwq(struct work_struct *work)
  * @work: the work item of interest
  *
  * Pools are created and destroyed under wq_pool_mutex, and allows read
- * access under sched-RCU read lock.  As such, this function should be
- * called under wq_pool_mutex or with preemption disabled.
+ * access under RCU read lock.  As such, this function should be
+ * called under wq_pool_mutex or inside of a rcu_read_lock() region.
  *
  * 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
@@ -1133,7 +1133,7 @@ static void put_pwq_unlocked(struct pool_workqueue *pwq)
 {
        if (pwq) {
                /*
-                * As both pwqs and pools are sched-RCU protected, the
+                * As both pwqs and pools are RCU protected, the
                 * following lock operations are safe.
                 */
                spin_lock_irq(&pwq->pool->lock);
@@ -1261,6 +1261,7 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
        if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
                return 0;
 
+       rcu_read_lock();
        /*
         * The queueing is in progress, or it is already queued. Try to
         * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
@@ -1299,10 +1300,12 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
                set_work_pool_and_keep_pending(work, pool->id);
 
                spin_unlock(&pool->lock);
+               rcu_read_unlock();
                return 1;
        }
        spin_unlock(&pool->lock);
 fail:
+       rcu_read_unlock();
        local_irq_restore(*flags);
        if (work_is_canceling(work))
                return -ENOENT;
@@ -1416,6 +1419,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
        if (unlikely(wq->flags & __WQ_DRAINING) &&
            WARN_ON_ONCE(!is_chained_work(wq)))
                return;
+       rcu_read_lock();
 retry:
        if (req_cpu == WORK_CPU_UNBOUND)
                cpu = wq_select_unbound_cpu(raw_smp_processor_id());
@@ -1472,10 +1476,8 @@ retry:
        /* pwq determined, queue */
        trace_workqueue_queue_work(req_cpu, pwq, work);
 
-       if (WARN_ON(!list_empty(&work->entry))) {
-               spin_unlock(&pwq->pool->lock);
-               return;
-       }
+       if (WARN_ON(!list_empty(&work->entry)))
+               goto out;
 
        pwq->nr_in_flight[pwq->work_color]++;
        work_flags = work_color_to_flags(pwq->work_color);
@@ -1493,7 +1495,9 @@ retry:
 
        insert_work(pwq, work, worklist, work_flags);
 
+out:
        spin_unlock(&pwq->pool->lock);
+       rcu_read_unlock();
 }
 
 /**
@@ -2975,14 +2979,14 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
 
        might_sleep();
 
-       local_irq_disable();
+       rcu_read_lock();
        pool = get_work_pool(work);
        if (!pool) {
-               local_irq_enable();
+               rcu_read_unlock();
                return false;
        }
 
-       spin_lock(&pool->lock);
+       spin_lock_irq(&pool->lock);
        /* see the comment in try_to_grab_pending() with the same code */
        pwq = get_work_pwq(work);
        if (pwq) {
@@ -3014,10 +3018,11 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
                lock_map_acquire(&pwq->wq->lockdep_map);
                lock_map_release(&pwq->wq->lockdep_map);
        }
-
+       rcu_read_unlock();
        return true;
 already_gone:
        spin_unlock_irq(&pool->lock);
+       rcu_read_unlock();
        return false;
 }
 
@@ -3504,7 +3509,7 @@ static void rcu_free_pool(struct rcu_head *rcu)
  * put_unbound_pool - put a worker_pool
  * @pool: worker_pool to put
  *
- * Put @pool.  If its refcnt reaches zero, it gets destroyed in sched-RCU
+ * Put @pool.  If its refcnt reaches zero, it gets destroyed in RCU
  * safe manner.  get_unbound_pool() calls this function on its failure path
  * and this function should be able to release pools which went through,
  * successfully or not, init_worker_pool().
@@ -3558,7 +3563,7 @@ static void put_unbound_pool(struct worker_pool *pool)
        del_timer_sync(&pool->idle_timer);
        del_timer_sync(&pool->mayday_timer);
 
-       /* sched-RCU protected to allow dereferences from get_work_pool() */
+       /* RCU protected to allow dereferences from get_work_pool() */
        call_rcu(&pool->rcu, rcu_free_pool);
 }
 
@@ -4472,7 +4477,8 @@ bool workqueue_congested(int cpu, struct workqueue_struct *wq)
        struct pool_workqueue *pwq;
        bool ret;
 
-       rcu_read_lock_sched();
+       rcu_read_lock();
+       preempt_disable();
 
        if (cpu == WORK_CPU_UNBOUND)
                cpu = smp_processor_id();
@@ -4483,7 +4489,8 @@ bool workqueue_congested(int cpu, struct workqueue_struct *wq)
                pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
 
        ret = !list_empty(&pwq->delayed_works);
-       rcu_read_unlock_sched();
+       preempt_enable();
+       rcu_read_unlock();
 
        return ret;
 }
@@ -4509,15 +4516,15 @@ unsigned int work_busy(struct work_struct *work)
        if (work_pending(work))
                ret |= WORK_BUSY_PENDING;
 
-       local_irq_save(flags);
+       rcu_read_lock();
        pool = get_work_pool(work);
        if (pool) {
-               spin_lock(&pool->lock);
+               spin_lock_irqsave(&pool->lock, flags);
                if (find_worker_executing_work(pool, work))
                        ret |= WORK_BUSY_RUNNING;
-               spin_unlock(&pool->lock);
+               spin_unlock_irqrestore(&pool->lock, flags);
        }
-       local_irq_restore(flags);
+       rcu_read_unlock();
 
        return ret;
 }
@@ -4701,7 +4708,7 @@ void show_workqueue_state(void)
        unsigned long flags;
        int pi;
 
-       rcu_read_lock_sched();
+       rcu_read_lock();
 
        pr_info("Showing busy workqueues and worker pools:\n");
 
@@ -4766,7 +4773,7 @@ void show_workqueue_state(void)
                touch_nmi_watchdog();
        }
 
-       rcu_read_unlock_sched();
+       rcu_read_unlock();
 }
 
 /* used to show worker information through /proc/PID/{comm,stat,status} */
@@ -5153,16 +5160,16 @@ bool freeze_workqueues_busy(void)
                 * nr_active is monotonically decreasing.  It's safe
                 * to peek without lock.
                 */
-               rcu_read_lock_sched();
+               rcu_read_lock();
                for_each_pwq(pwq, wq) {
                        WARN_ON_ONCE(pwq->nr_active < 0);
                        if (pwq->nr_active) {
                                busy = true;
-                               rcu_read_unlock_sched();
+                               rcu_read_unlock();
                                goto out_unlock;
                        }
                }
-               rcu_read_unlock_sched();
+               rcu_read_unlock();
        }
 out_unlock:
        mutex_unlock(&wq_pool_mutex);
@@ -5357,7 +5364,8 @@ static ssize_t wq_pool_ids_show(struct device *dev,
        const char *delim = "";
        int node, written = 0;
 
-       rcu_read_lock_sched();
+       get_online_cpus();
+       rcu_read_lock();
        for_each_node(node) {
                written += scnprintf(buf + written, PAGE_SIZE - written,
                                     "%s%d:%d", delim, node,
@@ -5365,7 +5373,8 @@ static ssize_t wq_pool_ids_show(struct device *dev,
                delim = " ";
        }
        written += scnprintf(buf + written, PAGE_SIZE - written, "\n");
-       rcu_read_unlock_sched();
+       rcu_read_unlock();
+       put_online_cpus();
 
        return written;
 }