When two blkdev_open() calls race with device removal and recreation,
__blkdev_get() can use looked up gendisk after it is freed:
CPU0 CPU1 CPU2
del_gendisk(disk);
bdev_unhash_inode(inode);
blkdev_open() blkdev_open()
bdev = bd_acquire(inode);
- creates and returns new inode
bdev = bd_acquire(inode);
- returns the same inode
__blkdev_get(devt) __blkdev_get(devt)
disk = get_gendisk(devt);
- got structure of device going away
<finish device removal>
<new device gets
created under the same
device number>
disk = get_gendisk(devt);
- got new device structure
if (!bdev->bd_openers) {
does the first open
}
if (!bdev->bd_openers)
- false
} else {
put_disk_and_module(disk)
- remember this was old device - this was last ref and disk is
now freed
}
disk_unblock_events(disk); -> oops
Fix the problem by making sure we drop reference to disk in
__blkdev_get() only after we are really done with it.
Reported-by: Hou Tao <houtao1@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/block_dev.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1dbbf847911a..fe41a76769fa 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1409,6 +1409,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
int ret;
int partno;
int perm = 0;
+ bool first_open = false;
if (mode & FMODE_READ)
perm |= MAY_READ;
@@ -1435,6 +1436,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
disk_block_events(disk);
mutex_lock_nested(&bdev->bd_mutex, for_part);
if (!bdev->bd_openers) {
+ first_open = true;
bdev->bd_disk = disk;
bdev->bd_queue = disk->queue;
bdev->bd_contains = bdev;
@@ -1520,14 +1522,15 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
if (ret)
goto out_unlock_bdev;
}
- /* only one opener holds refs to the module and disk */
- put_disk_and_module(disk);
}
bdev->bd_openers++;
if (for_part)
bdev->bd_part_count++;
mutex_unlock(&bdev->bd_mutex);
disk_unblock_events(disk);
+ /* only one opener holds refs to the module and disk */
+ if (!first_open)
+ put_disk_and_module(disk);
return 0;
out_clear:
--
2.13.6
