From 9b935bf300d3d2b06dd3f6673f7bf5bb914af84e Mon Sep 17 00:00:00 2001
From: Jens Axboe <jens.axboe@oracle.com>
Date: Wed, 28 May 2008 14:46:59 +0200
Subject: [PATCH] --- yaml --- r: 97419 b: refs/heads/master c:
 d6de8be711b28049a5cb93c954722c311c7d3f7f h: refs/heads/master i:   97417:
 cf8d7f9d469abc77ca4c5b4b52f066ab1fc45431   97415:
 01fc6fcc345dfc21288347142eaaaa21747d74f3 v: v3

---
 [refs]                    |  2 +-
 trunk/block/cfq-iosched.c | 28 ++++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/[refs] b/[refs]
index 66ce4f49bf94..0aec8e30f1d1 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 64565911cdb57c2f512a9715b985b5617402cc67
+refs/heads/master: d6de8be711b28049a5cb93c954722c311c7d3f7f
diff --git a/trunk/block/cfq-iosched.c b/trunk/block/cfq-iosched.c
index 4df3f0522435..d01b411c72f0 100644
--- a/trunk/block/cfq-iosched.c
+++ b/trunk/block/cfq-iosched.c
@@ -1142,6 +1142,9 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
 	kmem_cache_free(cfq_pool, cfqq);
 }
 
+/*
+ * Must always be called with the rcu_read_lock() held
+ */
 static void
 __call_for_each_cic(struct io_context *ioc,
 		    void (*func)(struct io_context *, struct cfq_io_context *))
@@ -1197,6 +1200,11 @@ static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
 	cfq_cic_free(cic);
 }
 
+/*
+ * Must be called with rcu_read_lock() held or preemption otherwise disabled.
+ * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
+ * and ->trim() which is called with the task lock held
+ */
 static void cfq_free_io_context(struct io_context *ioc)
 {
 	/*
@@ -1502,20 +1510,24 @@ static struct cfq_io_context *
 cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
 {
 	struct cfq_io_context *cic;
+	unsigned long flags;
 	void *k;
 
 	if (unlikely(!ioc))
 		return NULL;
 
+	rcu_read_lock();
+
 	/*
 	 * we maintain a last-hit cache, to avoid browsing over the tree
 	 */
 	cic = rcu_dereference(ioc->ioc_data);
-	if (cic && cic->key == cfqd)
+	if (cic && cic->key == cfqd) {
+		rcu_read_unlock();
 		return cic;
+	}
 
 	do {
-		rcu_read_lock();
 		cic = radix_tree_lookup(&ioc->radix_root, (unsigned long) cfqd);
 		rcu_read_unlock();
 		if (!cic)
@@ -1524,10 +1536,13 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
 		k = cic->key;
 		if (unlikely(!k)) {
 			cfq_drop_dead_cic(cfqd, ioc, cic);
+			rcu_read_lock();
 			continue;
 		}
 
+		spin_lock_irqsave(&ioc->lock, flags);
 		rcu_assign_pointer(ioc->ioc_data, cic);
+		spin_unlock_irqrestore(&ioc->lock, flags);
 		break;
 	} while (1);
 
@@ -2134,6 +2149,10 @@ static void *cfq_init_queue(struct request_queue *q)
 
 static void cfq_slab_kill(void)
 {
+	/*
+	 * Caller already ensured that pending RCU callbacks are completed,
+	 * so we should have no busy allocations at this point.
+	 */
 	if (cfq_pool)
 		kmem_cache_destroy(cfq_pool);
 	if (cfq_ioc_pool)
@@ -2292,6 +2311,11 @@ static void __exit cfq_exit(void)
 	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(ioc_count))
 		wait_for_completion(ioc_gone);
 	cfq_slab_kill();