block, cfq: move io_cq exit/release to blk-ioc.c

With kmem_cache managed by blk-ioc, io_cq exit/release can be moved to
blk-ioc too.  The odd ->io_cq->exit/release() callbacks are replaced
with elevator_ops->elevator_exit_icq_fn() with unlinking from both ioc
and q, and freeing automatically handled by blk-ioc.  The elevator
operation only need to perform exit operation specific to the elevator
- in cfq's case, exiting the cfqq's.

Also, clearing of io_cq's on q detach is moved to block core and
automatically performed on elevator switch and q release.

Because the q io_cq points to might be freed before RCU callback for
the io_cq runs, blk-ioc code should remember to which cache the io_cq
needs to be freed when the io_cq is released.  New field
io_cq->__rcu_icq_cache is added for this purpose.  As both the new
field and rcu_head are used only after io_cq is released and the
q/ioc_node fields aren't, they are put into unions.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

5 files changed, 78 insertions, 55 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 87ecc98b8ade..0910a5584d38 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -44,6 +44,51 @@ EXPORT_SYMBOL(get_io_context);
 #define ioc_release_depth_dec(q)        do { } while (0)
 #endif
 
+static void icq_free_icq_rcu(struct rcu_head *head)
+{
+        struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
+
+        kmem_cache_free(icq->__rcu_icq_cache, icq);
+}
+
+/*
+ * Exit and free an icq.  Called with both ioc and q locked.
+ */
+static void ioc_exit_icq(struct io_cq *icq)
+{
+        struct io_context *ioc = icq->ioc;
+        struct request_queue *q = icq->q;
+        struct elevator_type *et = q->elevator->type;
+
+        lockdep_assert_held(&ioc->lock);
+        lockdep_assert_held(q->queue_lock);
+
+        radix_tree_delete(&ioc->icq_tree, icq->q->id);
+        hlist_del_init(&icq->ioc_node);
+        list_del_init(&icq->q_node);
+
+        /*
+         * Both setting lookup hint to and clearing it from @icq are done
+         * under queue_lock.  If it's not pointing to @icq now, it never
+         * will.  Hint assignment itself can race safely.
+         */
+        if (rcu_dereference_raw(ioc->icq_hint) == icq)
+                rcu_assign_pointer(ioc->icq_hint, NULL);
+
+        if (et->ops.elevator_exit_icq_fn) {
+                ioc_release_depth_inc(q);
+                et->ops.elevator_exit_icq_fn(icq);
+                ioc_release_depth_dec(q);
+        }
+
+        /*
+         * @icq->q might have gone away by the time RCU callback runs
+         * making it impossible to determine icq_cache.  Record it in @icq.
+         */
+        icq->__rcu_icq_cache = et->icq_cache;
+        call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
+}
+
 /*
  * Slow path for ioc release in put_io_context().  Performs double-lock
  * dancing to unlink all icq's and then frees ioc.
@@ -87,10 +132,7 @@ static void ioc_release_fn(struct work_struct *work)
                         spin_lock(&ioc->lock);
                         continue;
                 }
-                ioc_release_depth_inc(this_q);
-                icq->exit(icq);
-                icq->release(icq);
-                ioc_release_depth_dec(this_q);
+                ioc_exit_icq(icq);
         }
 
         if (last_q) {
@@ -167,10 +209,7 @@ void put_io_context(struct io_context *ioc, struct request_queue *locked_q)
                         last_q = this_q;
                         continue;
                 }
-                ioc_release_depth_inc(this_q);
-                icq->exit(icq);
-                icq->release(icq);
-                ioc_release_depth_dec(this_q);
+                ioc_exit_icq(icq);
         }
 
         if (last_q && last_q != locked_q)
@@ -203,6 +242,27 @@ void exit_io_context(struct task_struct *task)
         put_io_context(ioc, NULL);
 }
 
+/**
+ * ioc_clear_queue - break any ioc association with the specified queue
+ * @q: request_queue being cleared
+ *
+ * Walk @q->icq_list and exit all io_cq's.  Must be called with @q locked.
+ */
+void ioc_clear_queue(struct request_queue *q)
+{
+        lockdep_assert_held(q->queue_lock);
+
+        while (!list_empty(&q->icq_list)) {
+                struct io_cq *icq = list_entry(q->icq_list.next,
+                                               struct io_cq, q_node);
+                struct io_context *ioc = icq->ioc;
+
+                spin_lock(&ioc->lock);
+                ioc_exit_icq(icq);
+                spin_unlock(&ioc->lock);
+        }
+}
+
 void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_flags,
                                 int node)
 {
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 5b4b4ab5e785..cf150011d808 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -479,8 +479,12 @@ static void blk_release_queue(struct kobject *kobj)
 
         blk_sync_queue(q);
 
-        if (q->elevator)
+        if (q->elevator) {
+                spin_lock_irq(q->queue_lock);
+                ioc_clear_queue(q);
+                spin_unlock_irq(q->queue_lock);
                 elevator_exit(q->elevator);
+        }
 
         blk_throtl_exit(q);
 
diff --git a/block/blk.h b/block/blk.h
index 3c510a4b5054..ed4d9bf2ab16 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -200,6 +200,7 @@ static inline int blk_do_io_stat(struct request *rq)
  */
 void get_io_context(struct io_context *ioc);
 struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q);
+void ioc_clear_queue(struct request_queue *q);
 
 void create_io_context_slowpath(struct task_struct *task, gfp_t gfp_mask,
                                 int node);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 06e59abcb57f..f6d315551496 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2674,26 +2674,6 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
         cfq_put_cfqg(cfqg);
 }
 
-static void cfq_icq_free_rcu(struct rcu_head *head)
-{
-        kmem_cache_free(cfq_icq_pool,
-                        icq_to_cic(container_of(head, struct io_cq, rcu_head)));
-}
-
-static void cfq_icq_free(struct io_cq *icq)
-{
-        call_rcu(&icq->rcu_head, cfq_icq_free_rcu);
-}
-
-static void cfq_release_icq(struct io_cq *icq)
-{
-        struct io_context *ioc = icq->ioc;
-
-        radix_tree_delete(&ioc->icq_tree, icq->q->id);
-        hlist_del(&icq->ioc_node);
-        cfq_icq_free(icq);
-}
-
 static void cfq_put_cooperator(struct cfq_queue *cfqq)
 {
         struct cfq_queue *__cfqq, *next;
@@ -2731,17 +2711,6 @@ static void cfq_exit_icq(struct io_cq *icq)
 {
         struct cfq_io_cq *cic = icq_to_cic(icq);
         struct cfq_data *cfqd = cic_to_cfqd(cic);
-        struct io_context *ioc = icq->ioc;
-
-        list_del_init(&icq->q_node);
-
-        /*
-         * Both setting lookup hint to and clearing it from @icq are done
-         * under queue_lock.  If it's not pointing to @icq now, it never
-         * will.  Hint assignment itself can race safely.
-         */
-        if (rcu_dereference_raw(ioc->icq_hint) == icq)
-                rcu_assign_pointer(ioc->icq_hint, NULL);
 
         if (cic->cfqq[BLK_RW_ASYNC]) {
                 cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
@@ -2764,8 +2733,6 @@ static struct cfq_io_cq *cfq_alloc_cic(struct cfq_data *cfqd, gfp_t gfp_mask)
                 cic->ttime.last_end_request = jiffies;
                 INIT_LIST_HEAD(&cic->icq.q_node);
                 INIT_HLIST_NODE(&cic->icq.ioc_node);
-                cic->icq.exit = cfq_exit_icq;
-                cic->icq.release = cfq_release_icq;
         }
 
         return cic;
@@ -3034,7 +3001,7 @@ out:
         if (ret)
                 printk(KERN_ERR "cfq: icq link failed!\n");
         if (icq)
-                cfq_icq_free(icq);
+                kmem_cache_free(cfq_icq_pool, icq);
         return ret;
 }
 
@@ -3774,17 +3741,6 @@ static void cfq_exit_queue(struct elevator_queue *e)
         if (cfqd->active_queue)
                 __cfq_slice_expired(cfqd, cfqd->active_queue, 0);
 
-        while (!list_empty(&q->icq_list)) {
-                struct io_cq *icq = list_entry(q->icq_list.next,
-                                               struct io_cq, q_node);
-                struct io_context *ioc = icq->ioc;
-
-                spin_lock(&ioc->lock);
-                cfq_exit_icq(icq);
-                cfq_release_icq(icq);
-                spin_unlock(&ioc->lock);
-        }
-
         cfq_put_async_queues(cfqd);
         cfq_release_cfq_groups(cfqd);
 
@@ -4019,6 +3975,7 @@ static struct elevator_type iosched_cfq = {
                 .elevator_completed_req_fn =    cfq_completed_request,
                 .elevator_former_req_fn =       elv_rb_former_request,
                 .elevator_latter_req_fn =       elv_rb_latter_request,
+                .elevator_exit_icq_fn =         cfq_exit_icq,
                 .elevator_set_req_fn =          cfq_set_request,
                 .elevator_put_req_fn =          cfq_put_request,
                 .elevator_may_queue_fn =        cfq_may_queue,
diff --git a/block/elevator.c b/block/elevator.c
index cca049fb45c8..91e18f8af9be 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -979,8 +979,9 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
                         goto fail_register;
         }
 
-        /* done, replace the old one with new one and turn off BYPASS */
+        /* done, clear io_cq's, switch elevators and turn off BYPASS */
         spin_lock_irq(q->queue_lock);
+        ioc_clear_queue(q);
         old_elevator = q->elevator;
         q->elevator = e;
         spin_unlock_irq(q->queue_lock);