block, cfq: kill ioc_gone

Now that cic's are immediately unlinked under both locks, there's no
need to count and drain cic's before module unload.  RCU callback
completion is waited with rcu_barrier().

While at it, remove residual RCU operations on cic_list.

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

1 files changed, 5 insertions, 38 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ff44435fad50..ae7791a8ded9 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -62,10 +62,6 @@ static const int cfq_hist_divisor = 4;
 static struct kmem_cache *cfq_pool;
 static struct kmem_cache *cfq_ioc_pool;
 
-static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
-static struct completion *ioc_gone;
-static DEFINE_SPINLOCK(ioc_gone_lock);
-
 #define CFQ_PRIO_LISTS          IOPRIO_BE_NR
 #define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
 #define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)
@@ -2671,26 +2667,8 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
 
 static void cfq_cic_free_rcu(struct rcu_head *head)
 {
-        struct cfq_io_context *cic;
-
-        cic = container_of(head, struct cfq_io_context, rcu_head);
-
-        kmem_cache_free(cfq_ioc_pool, cic);
-        elv_ioc_count_dec(cfq_ioc_count);
-
-        if (ioc_gone) {
-                /*
-                 * CFQ scheduler is exiting, grab exit lock and check
-                 * the pending io context count. If it hits zero,
-                 * complete ioc_gone and set it back to NULL
-                 */
-                spin_lock(&ioc_gone_lock);
-                if (ioc_gone && !elv_ioc_count_read(cfq_ioc_count)) {
-                        complete(ioc_gone);
-                        ioc_gone = NULL;
-                }
-                spin_unlock(&ioc_gone_lock);
-        }
+        kmem_cache_free(cfq_ioc_pool,
+                        container_of(head, struct cfq_io_context, rcu_head));
 }
 
 static void cfq_cic_free(struct cfq_io_context *cic)
@@ -2705,7 +2683,7 @@ static void cfq_release_cic(struct cfq_io_context *cic)
 
         BUG_ON(!(dead_key & CIC_DEAD_KEY));
         radix_tree_delete(&ioc->radix_root, dead_key >> CIC_DEAD_INDEX_SHIFT);
-        hlist_del_rcu(&cic->cic_list);
+        hlist_del(&cic->cic_list);
         cfq_cic_free(cic);
 }
 
@@ -2782,7 +2760,6 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
                 INIT_HLIST_NODE(&cic->cic_list);
                 cic->exit = cfq_exit_cic;
                 cic->release = cfq_release_cic;
-                elv_ioc_count_inc(cfq_ioc_count);
         }
 
         return cic;
@@ -3072,7 +3049,7 @@ static int cfq_create_cic(struct cfq_data *cfqd, gfp_t gfp_mask)
 
         ret = radix_tree_insert(&ioc->radix_root, q->id, cic);
         if (likely(!ret)) {
-                hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
+                hlist_add_head(&cic->cic_list, &ioc->cic_list);
                 list_add(&cic->queue_list, &cfqd->cic_list);
                 cic = NULL;
         } else if (ret == -EEXIST) {
@@ -4156,19 +4133,9 @@ static int __init cfq_init(void)
 
 static void __exit cfq_exit(void)
 {
-        DECLARE_COMPLETION_ONSTACK(all_gone);
         blkio_policy_unregister(&blkio_policy_cfq);
         elv_unregister(&iosched_cfq);
-        ioc_gone = &all_gone;
-        /* ioc_gone's update must be visible before reading ioc_count */
-        smp_wmb();
-
-        /*
-         * this also protects us from entering cfq_slab_kill() with
-         * pending RCU callbacks
-         */
-        if (elv_ioc_count_read(cfq_ioc_count))
-                wait_for_completion(&all_gone);
+        rcu_barrier();  /* make sure all cic RCU frees are complete */
         cfq_slab_kill();
 }