[PATCH] block: fix block_class iteration locking

[Tejun Heo <tj@kernel.org>]

genhd.c used block_class_lock when it wants to iterate over
block_class.devices list.  This is incorrect as block_class_lock has
nothing to do with synchronization around block_class.devices list, so
there's a window, albeit small, where the list can change while it's
being iterated over.  Fix it by using block_class.sem instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 block/genhd.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index b922d48..b646e7e 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -234,7 +234,7 @@ void __init printk_all_partitions(void)
 	char buf[BDEVNAME_SIZE];
 	int n;
 
-	mutex_lock(&block_class_lock);
+	down(&block_class.sem);
 	/* For each block device... */
 	list_for_each_entry(dev, &block_class.devices, node) {
 		if (dev->type != &disk_type)
@@ -275,7 +275,7 @@ void __init printk_all_partitions(void)
 		}
 	}
 
-	mutex_unlock(&block_class_lock);
+	up(&block_class.sem);
 }
 
 #ifdef CONFIG_PROC_FS
@@ -285,7 +285,7 @@ static void *part_start(struct seq_file *part, loff_t *pos)
 	loff_t k = *pos;
 	struct device *dev;
 
-	mutex_lock(&block_class_lock);
+	down(&block_class.sem);
 	list_for_each_entry(dev, &block_class.devices, node) {
 		if (dev->type != &disk_type)
 			continue;
@@ -311,7 +311,7 @@ static void *part_next(struct seq_file *part, void *v, loff_t *pos)
 
 static void part_stop(struct seq_file *part, void *v)
 {
-	mutex_unlock(&block_class_lock);
+	up(&block_class.sem);
 }
 
 static int show_partition(struct seq_file *part, void *v)
@@ -533,7 +533,7 @@ static void *diskstats_start(struct seq_file *part, loff_t *pos)
 	loff_t k = *pos;
 	struct device *dev;
 
-	mutex_lock(&block_class_lock);
+	down(&block_class.sem);
 	list_for_each_entry(dev, &block_class.devices, node) {
 		if (dev->type != &disk_type)
 			continue;
@@ -560,7 +560,7 @@ static void *diskstats_next(struct seq_file *part, void *v, loff_t *pos)
 
 static void diskstats_stop(struct seq_file *part, void *v)
 {
-	mutex_unlock(&block_class_lock);
+	up(&block_class.sem);
 }
 
 static int diskstats_show(struct seq_file *s, void *v)
@@ -658,7 +658,7 @@ dev_t blk_lookup_devt(const char *name, int part)
 	struct device *dev;
 	dev_t devt = MKDEV(0, 0);
 
-	mutex_lock(&block_class_lock);
+	down(&block_class.sem);
 	list_for_each_entry(dev, &block_class.devices, node) {
 		if (dev->type != &disk_type)
 			continue;
@@ -671,7 +671,7 @@ dev_t blk_lookup_devt(const char *name, int part)
 			break;
 		}
 	}
-	mutex_unlock(&block_class_lock);
+	up(&block_class.sem);
 
 	return devt;
 }
-- 
1.5.4.5