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-rw-r--r--block/cfq-iosched.c67
1 files changed, 35 insertions, 32 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 181a63d..e617b08 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1682,12 +1682,19 @@ static int cfq_allow_merge(struct request_queue *q, struct request *rq,
return false;
/*
- * Lookup the cfqq that this bio will be queued with. Allow
- * merge only if rq is queued there.
+ * Lookup the cfqq that this bio will be queued with and allow
+ * merge only if rq is queued there. This function can be called
+ * from plug merge without queue_lock. In such cases, ioc of @rq
+ * and %current are guaranteed to be equal. Avoid lookup which
+ * requires queue_lock by using @rq's cic.
*/
- cic = cfq_cic_lookup(cfqd, current->io_context);
- if (!cic)
- return false;
+ if (current->io_context == RQ_CIC(rq)->ioc) {
+ cic = RQ_CIC(rq);
+ } else {
+ cic = cfq_cic_lookup(cfqd, current->io_context);
+ if (!cic)
+ return false;
+ }
cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
return cfqq == RQ_CFQQ(rq);
@@ -2784,21 +2791,15 @@ static void cfq_exit_cic(struct cfq_io_context *cic)
struct io_context *ioc = cic->ioc;
list_del_init(&cic->queue_list);
+ cic->key = cfqd_dead_key(cfqd);
/*
- * Make sure dead mark is seen for dead queues
+ * Both setting lookup hint to and clearing it from @cic are done
+ * under queue_lock. If it's not pointing to @cic now, it never
+ * will. Hint assignment itself can race safely.
*/
- smp_wmb();
- cic->key = cfqd_dead_key(cfqd);
-
- rcu_read_lock();
- if (rcu_dereference(ioc->ioc_data) == cic) {
- rcu_read_unlock();
- spin_lock(&ioc->lock);
+ if (rcu_dereference_raw(ioc->ioc_data) == cic)
rcu_assign_pointer(ioc->ioc_data, NULL);
- spin_unlock(&ioc->lock);
- } else
- rcu_read_unlock();
if (cic->cfqq[BLK_RW_ASYNC]) {
cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
@@ -3092,12 +3093,20 @@ cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
cfq_cic_free(cic);
}
+/**
+ * cfq_cic_lookup - lookup cfq_io_context
+ * @cfqd: the associated cfq_data
+ * @ioc: the associated io_context
+ *
+ * Look up cfq_io_context associated with @cfqd - @ioc pair. Must be
+ * called with queue_lock held.
+ */
static struct cfq_io_context *
cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
{
struct cfq_io_context *cic;
- unsigned long flags;
+ lockdep_assert_held(cfqd->queue->queue_lock);
if (unlikely(!ioc))
return NULL;
@@ -3107,28 +3116,22 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
* we maintain a last-hit cache, to avoid browsing over the tree
*/
cic = rcu_dereference(ioc->ioc_data);
- if (cic && cic->key == cfqd) {
- rcu_read_unlock();
- return cic;
- }
+ if (cic && cic->key == cfqd)
+ goto out;
do {
cic = radix_tree_lookup(&ioc->radix_root, cfqd->queue->id);
- rcu_read_unlock();
if (!cic)
break;
- if (unlikely(cic->key != cfqd)) {
- cfq_drop_dead_cic(cfqd, ioc, cic);
- rcu_read_lock();
- continue;
+ if (likely(cic->key == cfqd)) {
+ /* hint assignment itself can race safely */
+ rcu_assign_pointer(ioc->ioc_data, cic);
+ break;
}
-
- spin_lock_irqsave(&ioc->lock, flags);
- rcu_assign_pointer(ioc->ioc_data, cic);
- spin_unlock_irqrestore(&ioc->lock, flags);
- break;
+ cfq_drop_dead_cic(cfqd, ioc, cic);
} while (1);
-
+out:
+ rcu_read_unlock();
return cic;
}
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