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Subject[PATCH] block: fix block_class iteration locking
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


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