workqueue: increase max_active of keventd and kill current_is_keventd()

Define WQ_MAX_ACTIVE and create keventd with max_active set to half of
it which means that keventd now can process upto WQ_MAX_ACTIVE / 2 - 1
works concurrently.  Unless some combination can result in dependency
loop longer than max_active, deadlock won't happen and thus it's
unnecessary to check whether current_is_keventd() before trying to
schedule a work.  Kill current_is_keventd().

(Lockdep annotations are broken.  We need lock_map_acquire_read_norecurse())

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>

1 files changed, 13 insertions, 50 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0ad46523b423..4190e84cf995 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2398,7 +2398,6 @@ EXPORT_SYMBOL(schedule_delayed_work_on);
 int schedule_on_each_cpu(work_func_t func)
 {
         int cpu;
-        int orig = -1;
         struct work_struct *works;
 
         works = alloc_percpu(struct work_struct);
@@ -2407,23 +2406,12 @@ int schedule_on_each_cpu(work_func_t func)
 
         get_online_cpus();
 
-        /*
-         * When running in keventd don't schedule a work item on
-         * itself.  Can just call directly because the work queue is
-         * already bound.  This also is faster.
-         */
-        if (current_is_keventd())
-                orig = raw_smp_processor_id();
-
         for_each_online_cpu(cpu) {
                 struct work_struct *work = per_cpu_ptr(works, cpu);
 
                 INIT_WORK(work, func);
-                if (cpu != orig)
-                        schedule_work_on(cpu, work);
+                schedule_work_on(cpu, work);
         }
-        if (orig >= 0)
-                func(per_cpu_ptr(works, orig));
 
         for_each_online_cpu(cpu)
                 flush_work(per_cpu_ptr(works, cpu));
@@ -2494,41 +2482,6 @@ int keventd_up(void)
         return keventd_wq != NULL;
 }
 
-int current_is_keventd(void)
-{
-        bool found = false;
-        unsigned int cpu;
-
-        /*
-         * There no longer is one-to-one relation between worker and
-         * work queue and a worker task might be unbound from its cpu
-         * if the cpu was offlined.  Match all busy workers.  This
-         * function will go away once dynamic pool is implemented.
-         */
-        for_each_possible_cpu(cpu) {
-                struct global_cwq *gcwq = get_gcwq(cpu);
-                struct worker *worker;
-                struct hlist_node *pos;
-                unsigned long flags;
-                int i;
-
-                spin_lock_irqsave(&gcwq->lock, flags);
-
-                for_each_busy_worker(worker, i, pos, gcwq) {
-                        if (worker->task == current) {
-                                found = true;
-                                break;
-                        }
-                }
-
-                spin_unlock_irqrestore(&gcwq->lock, flags);
-                if (found)
-                        break;
-        }
-
-        return found;
-}
-
 static struct cpu_workqueue_struct *alloc_cwqs(void)
 {
         /*
@@ -2576,6 +2529,16 @@ static void free_cwqs(struct cpu_workqueue_struct *cwqs)
 #endif
 }
 
+static int wq_clamp_max_active(int max_active, const char *name)
+{
+        if (max_active < 1 || max_active > WQ_MAX_ACTIVE)
+                printk(KERN_WARNING "workqueue: max_active %d requested for %s "
+                       "is out of range, clamping between %d and %d\n",
+                       max_active, name, 1, WQ_MAX_ACTIVE);
+
+        return clamp_val(max_active, 1, WQ_MAX_ACTIVE);
+}
+
 struct workqueue_struct *__create_workqueue_key(const char *name,
                                                 unsigned int flags,
                                                 int max_active,
@@ -2585,7 +2548,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
         struct workqueue_struct *wq;
         unsigned int cpu;
 
-        max_active = clamp_val(max_active, 1, INT_MAX);
+        max_active = wq_clamp_max_active(max_active, name);
 
         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
         if (!wq)
@@ -3324,6 +3287,6 @@ void __init init_workqueues(void)
                 spin_unlock_irq(&gcwq->lock);
         }
 
-        keventd_wq = create_workqueue("events");
+        keventd_wq = __create_workqueue("events", 0, WQ_DFL_ACTIVE);
         BUG_ON(!keventd_wq);
 }