[PATCH 1/2] block: add info when opening an exclusive opened block device for write

["zhangyi (F)" <yi.zhang@huawei.com>]

Opening an exclusive opened block device for write make the exclusive
open isn't exclusive enough, it may lead to data corruption when some
one writing data through the counterpart raw block device, such as
corrupt a mounted file system. This patch add an info message when
opening an exclusive opened block device for write to hint the
potential data corruption.

Note that there are some legal cases such as file system or device
mapper online resize, so this message is just a hint and isn't always
mean that a risky written happens.

Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
---
 fs/block_dev.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index bb28e2e..d92aa45 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1667,13 +1667,13 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 
 	res = __blkdev_get(bdev, mode, 0);
 
+	mutex_lock(&bdev->bd_mutex);
+	spin_lock(&bdev_lock);
+
 	if (whole) {
 		struct gendisk *disk = whole->bd_disk;
 
 		/* finish claiming */
-		mutex_lock(&bdev->bd_mutex);
-		spin_lock(&bdev_lock);
-
 		if (!res) {
 			BUG_ON(!bd_may_claim(bdev, whole, holder));
 			/*
@@ -1710,6 +1710,22 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 
 		mutex_unlock(&bdev->bd_mutex);
 		bdput(whole);
+	} else {
+		if (!res && (mode & FMODE_WRITE) && bdev->bd_holders) {
+			char name[BDEVNAME_SIZE];
+
+			/*
+			 * Open an exclusive opened device for write may
+			 * probability corrupt the device, such as a
+			 * mounted file system, give a hint here.
+			 */
+			pr_info_ratelimited("VFS: Open an exclusive opened "
+				    "block device for write %s [%d %s].\n",
+				    bdevname(bdev, name), current->pid,
+				    current->comm);
+		}
+		spin_unlock(&bdev_lock);
+		mutex_unlock(&bdev->bd_mutex);
 	}
 
 	return res;
-- 
2.7.4