1 files changed, 88 insertions, 47 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 8b782a63c297..fb95dd2f889a 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -36,11 +36,23 @@ static void icq_free_icq_rcu(struct rcu_head *head)
         kmem_cache_free(icq->__rcu_icq_cache, icq);
 }
 
-/*
- * Exit and free an icq.  Called with both ioc and q locked.
- */
+/* Exit an icq. Called with both ioc and q locked. */
 static void ioc_exit_icq(struct io_cq *icq)
 {
+        struct elevator_type *et = icq->q->elevator->type;
+
+        if (icq->flags & ICQ_EXITED)
+                return;
+
+        if (et->ops.elevator_exit_icq_fn)
+                et->ops.elevator_exit_icq_fn(icq);
+
+        icq->flags |= ICQ_EXITED;
+}
+
+/* Release an icq.  Called with both ioc and q locked. */
+static void ioc_destroy_icq(struct io_cq *icq)
+{
         struct io_context *ioc = icq->ioc;
         struct request_queue *q = icq->q;
         struct elevator_type *et = q->elevator->type;
@@ -60,8 +72,7 @@ static void ioc_exit_icq(struct io_cq *icq)
         if (rcu_dereference_raw(ioc->icq_hint) == icq)
                 rcu_assign_pointer(ioc->icq_hint, NULL);
 
-        if (et->ops.elevator_exit_icq_fn)
-                et->ops.elevator_exit_icq_fn(icq);
+        ioc_exit_icq(icq);
 
         /*
          * @icq->q might have gone away by the time RCU callback runs
@@ -79,7 +90,6 @@ static void ioc_release_fn(struct work_struct *work)
 {
         struct io_context *ioc = container_of(work, struct io_context,
                                               release_work);
-        struct request_queue *last_q = NULL;
         unsigned long flags;
 
         /*
@@ -93,44 +103,19 @@ static void ioc_release_fn(struct work_struct *work)
         while (!hlist_empty(&ioc->icq_list)) {
                 struct io_cq *icq = hlist_entry(ioc->icq_list.first,
                                                 struct io_cq, ioc_node);
-                struct request_queue *this_q = icq->q;
-
-                if (this_q != last_q) {
-                        /*
-                         * Need to switch to @this_q.  Once we release
-                         * @ioc->lock, it can go away along with @cic.
-                         * Hold on to it.
-                         */
-                        __blk_get_queue(this_q);
-
-                        /*
-                         * blk_put_queue() might sleep thanks to kobject
-                         * idiocy.  Always release both locks, put and
-                         * restart.
-                         */
-                        if (last_q) {
-                                spin_unlock(last_q->queue_lock);
-                                spin_unlock_irqrestore(&ioc->lock, flags);
-                                blk_put_queue(last_q);
-                        } else {
-                                spin_unlock_irqrestore(&ioc->lock, flags);
-                        }
-
-                        last_q = this_q;
-                        spin_lock_irqsave(this_q->queue_lock, flags);
-                        spin_lock_nested(&ioc->lock, 1);
-                        continue;
+                struct request_queue *q = icq->q;
+
+                if (spin_trylock(q->queue_lock)) {
+                        ioc_destroy_icq(icq);
+                        spin_unlock(q->queue_lock);
+                } else {
+                        spin_unlock_irqrestore(&ioc->lock, flags);
+                        cpu_relax();
+                        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
                 }
-                ioc_exit_icq(icq);
         }
 
-        if (last_q) {
-                spin_unlock(last_q->queue_lock);
-                spin_unlock_irqrestore(&ioc->lock, flags);
-                blk_put_queue(last_q);
-        } else {
-                spin_unlock_irqrestore(&ioc->lock, flags);
-        }
+        spin_unlock_irqrestore(&ioc->lock, flags);
 
         kmem_cache_free(iocontext_cachep, ioc);
 }
@@ -145,6 +130,7 @@ static void ioc_release_fn(struct work_struct *work)
 void put_io_context(struct io_context *ioc)
 {
         unsigned long flags;
+        bool free_ioc = false;
 
         if (ioc == NULL)
                 return;
@@ -159,8 +145,13 @@ void put_io_context(struct io_context *ioc)
                 spin_lock_irqsave(&ioc->lock, flags);
                 if (!hlist_empty(&ioc->icq_list))
                         schedule_work(&ioc->release_work);
+                else
+                        free_ioc = true;
                 spin_unlock_irqrestore(&ioc->lock, flags);
         }
+
+        if (free_ioc)
+                kmem_cache_free(iocontext_cachep, ioc);
 }
 EXPORT_SYMBOL(put_io_context);
 
@@ -168,13 +159,41 @@ EXPORT_SYMBOL(put_io_context);
 void exit_io_context(struct task_struct *task)
 {
         struct io_context *ioc;
+        struct io_cq *icq;
+        struct hlist_node *n;
+        unsigned long flags;
 
         task_lock(task);
         ioc = task->io_context;
         task->io_context = NULL;
         task_unlock(task);
 
-        atomic_dec(&ioc->nr_tasks);
+        if (!atomic_dec_and_test(&ioc->nr_tasks)) {
+                put_io_context(ioc);
+                return;
+        }
+
+        /*
+         * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
+         * reverse double locking.  Read comment in ioc_release_fn() for
+         * explanation on the nested locking annotation.
+         */
+retry:
+        spin_lock_irqsave_nested(&ioc->lock, flags, 1);
+        hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node) {
+                if (icq->flags & ICQ_EXITED)
+                        continue;
+                if (spin_trylock(icq->q->queue_lock)) {
+                        ioc_exit_icq(icq);
+                        spin_unlock(icq->q->queue_lock);
+                } else {
+                        spin_unlock_irqrestore(&ioc->lock, flags);
+                        cpu_relax();
+                        goto retry;
+                }
+        }
+        spin_unlock_irqrestore(&ioc->lock, flags);
+
         put_io_context(ioc);
 }
 
@@ -194,7 +213,7 @@ void ioc_clear_queue(struct request_queue *q)
                 struct io_context *ioc = icq->ioc;
 
                 spin_lock(&ioc->lock);
-                ioc_exit_icq(icq);
+                ioc_destroy_icq(icq);
                 spin_unlock(&ioc->lock);
         }
 }
@@ -363,13 +382,13 @@ struct io_cq *ioc_create_icq(struct request_queue *q, gfp_t gfp_mask)
         return icq;
 }
 
-void ioc_set_changed(struct io_context *ioc, int which)
+void ioc_set_icq_flags(struct io_context *ioc, unsigned int flags)
 {
         struct io_cq *icq;
         struct hlist_node *n;
 
         hlist_for_each_entry(icq, n, &ioc->icq_list, ioc_node)
-                set_bit(which, &icq->changed);
+                icq->flags |= flags;
 }
 
 /**
@@ -387,7 +406,7 @@ void ioc_ioprio_changed(struct io_context *ioc, int ioprio)
 
         spin_lock_irqsave(&ioc->lock, flags);
         ioc->ioprio = ioprio;
-        ioc_set_changed(ioc, ICQ_IOPRIO_CHANGED);
+        ioc_set_icq_flags(ioc, ICQ_IOPRIO_CHANGED);
         spin_unlock_irqrestore(&ioc->lock, flags);
 }
 
@@ -404,11 +423,33 @@ void ioc_cgroup_changed(struct io_context *ioc)
         unsigned long flags;
 
         spin_lock_irqsave(&ioc->lock, flags);
-        ioc_set_changed(ioc, ICQ_CGROUP_CHANGED);
+        ioc_set_icq_flags(ioc, ICQ_CGROUP_CHANGED);
         spin_unlock_irqrestore(&ioc->lock, flags);
 }
 EXPORT_SYMBOL(ioc_cgroup_changed);
 
+/**
+ * icq_get_changed - fetch and clear icq changed mask
+ * @icq: icq of interest
+ *
+ * Fetch and clear ICQ_*_CHANGED bits from @icq.  Grabs and releases
+ * @icq->ioc->lock.
+ */
+unsigned icq_get_changed(struct io_cq *icq)
+{
+        unsigned int changed = 0;
+        unsigned long flags;
+
+        if (unlikely(icq->flags & ICQ_CHANGED_MASK)) {
+                spin_lock_irqsave(&icq->ioc->lock, flags);
+                changed = icq->flags & ICQ_CHANGED_MASK;
+                icq->flags &= ~ICQ_CHANGED_MASK;
+                spin_unlock_irqrestore(&icq->ioc->lock, flags);
+        }
+        return changed;
+}
+EXPORT_SYMBOL(icq_get_changed);
+
 static int __init blk_ioc_init(void)
 {
         iocontext_cachep = kmem_cache_create("blkdev_ioc",