From 3b221a96c8b34ea9b898c8c39c80602537990f31 Mon Sep 17 00:00:00 2001
From: Paolo Valente <paolo.valente@unimore.it>
Date: Mon, 2 Aug 2010 20:38:02 +0200
Subject: [PATCH] Revert "Temporary revert "cfq-iosched: remove dead_key from cfq_io_context""

This reverts commit 4966e578ea55c52f5196aaef09ee267381433d2a,
to restore the original code status before adding bfq patches for 2.6.35
---
 block/cfq-iosched.c       |   41 ++++++++++++++++++++++++++++-------------
 include/linux/iocontext.h |    1 -
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 55a6150..e80a8fd 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -434,7 +434,24 @@ static inline void cic_set_cfqq(struct cfq_io_context *cic,
 	cic->cfqq[is_sync] = cfqq;
 }
 
+#define CIC_DEAD_KEY	1ul
 #define CIC_DEAD_INDEX_SHIFT	1
+
+static inline void *cfqd_dead_key(struct cfq_data *cfqd)
+{
+	return (void *)(cfqd->cic_index << CIC_DEAD_INDEX_SHIFT | CIC_DEAD_KEY);
+}
+
+static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)
+{
+	struct cfq_data *cfqd = cic->key;
+
+	if (unlikely((unsigned long) cfqd & CIC_DEAD_KEY))
+		return NULL;
+
+	return cfqd;
+}
+
 /*
  * We regard a request as SYNC, if it's either a read or has the SYNC bit
  * set (in which case it could also be direct WRITE).
@@ -2524,11 +2541,12 @@ static void cfq_cic_free(struct cfq_io_context *cic)
 static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
 {
 	unsigned long flags;
+	unsigned long dead_key = (unsigned long) cic->key;
 
-	BUG_ON(!cic->dead_key);
+	BUG_ON(!(dead_key & CIC_DEAD_KEY));
 
 	spin_lock_irqsave(&ioc->lock, flags);
-	radix_tree_delete(&ioc->radix_root, cic->dead_key);
+	radix_tree_delete(&ioc->radix_root, dead_key >> CIC_DEAD_INDEX_SHIFT);
 	hlist_del_rcu(&cic->cic_list);
 	spin_unlock_irqrestore(&ioc->lock, flags);
 
@@ -2592,11 +2610,10 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
 	list_del_init(&cic->queue_list);
 
 	/*
-	 * Make sure key == NULL is seen for dead queues
+	 * Make sure dead mark is seen for dead queues
 	 */
 	smp_wmb();
-	cic->dead_key = (unsigned long) cic->key;
-	cic->key = NULL;
+	cic->key = cfqd_dead_key(cfqd);
 
 	if (ioc->ioc_data == cic)
 		rcu_assign_pointer(ioc->ioc_data, NULL);
@@ -2615,7 +2632,7 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
 static void cfq_exit_single_io_context(struct io_context *ioc,
 				       struct cfq_io_context *cic)
 {
-	struct cfq_data *cfqd = cic->key;
+	struct cfq_data *cfqd = cic_to_cfqd(cic);
 
 	if (cfqd) {
 		struct request_queue *q = cfqd->queue;
@@ -2628,7 +2645,7 @@ static void cfq_exit_single_io_context(struct io_context *ioc,
 		 * race between exiting task and queue
 		 */
 		smp_read_barrier_depends();
-		if (cic->key)
+		if (cic->key == cfqd)
 			__cfq_exit_single_io_context(cfqd, cic);
 
 		spin_unlock_irqrestore(q->queue_lock, flags);
@@ -2708,7 +2725,7 @@ static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
 
 static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
 {
-	struct cfq_data *cfqd = cic->key;
+	struct cfq_data *cfqd = cic_to_cfqd(cic);
 	struct cfq_queue *cfqq;
 	unsigned long flags;
 
@@ -2764,7 +2781,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 static void changed_cgroup(struct io_context *ioc, struct cfq_io_context *cic)
 {
 	struct cfq_queue *sync_cfqq = cic_to_cfqq(cic, 1);
-	struct cfq_data *cfqd = cic->key;
+	struct cfq_data *cfqd = cic_to_cfqd(cic);
 	unsigned long flags;
 	struct request_queue *q;
 
@@ -2901,6 +2918,7 @@ cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
 	unsigned long flags;
 
 	WARN_ON(!list_empty(&cic->queue_list));
+	BUG_ON(cic->key != cfqd_dead_key(cfqd));
 
 	spin_lock_irqsave(&ioc->lock, flags);
 
@@ -2918,7 +2936,6 @@ 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;
@@ -2939,9 +2956,7 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
 		rcu_read_unlock();
 		if (!cic)
 			break;
-		/* ->key must be copied to avoid race with cfq_exit_queue() */
-		k = cic->key;
-		if (unlikely(!k)) {
+		if (unlikely(cic->key != cfqd)) {
 			cfq_drop_dead_cic(cfqd, ioc, cic);
 			rcu_read_lock();
 			continue;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index bbe110c..8c7e254 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -7,7 +7,6 @@
 
 struct cfq_io_context {
 	void *key;
-	unsigned long dead_key;
 
 	void *cfqq[2];
 
-- 
1.7.0.4