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>

1 files changed, 68 insertions, 8 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)
 {