FAILED: patch "[PATCH] bcache: register_bcache(): call blkdev_put() when" failed to apply to 4.7-stable tree

The patch below does not apply to the 4.7-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Eric Wheeler <[email protected]>
Date: Fri, 17 Jun 2016 15:01:54 -0700
Subject: [PATCH] bcache: register_bcache(): call blkdev_put() when
cache_alloc() fails

register_cache() is supposed to return an error string on error so that register_bcache() will will blkdev_put and cleanup other user counters, but it does not set 'char *err' when cache_alloc() fails (eg, due to memory pressure) and thus register_bcache() performs no cleanup.

register_bcache() <----------\ <- no jump to err_close, no blkdev_put()

   |                         |
   +->register_cache()       |  <- fails to set char *err
         |                   |
         +->cache_alloc() ---/  <- returns error

This patch sets char *err for this failure case so that register_cache() will cause register_bcache() to correctly jump to err_close and do cleanup. This was tested under OOM conditions that triggered the bug.

index 95a4ca6ce6ff..6ada14b9a157 100644
@@ -1844,7 +1844,7 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
 				struct block_device *bdev, struct cache *ca)
 {
 	char name[BDEVNAME_SIZE];
-	const char *err = NULL;
+	const char *err = NULL; /* must be set for any error case */
 	int ret = 0;
 
 	memcpy(&ca->sb, sb, sizeof(struct cache_sb));

@@ -1861,8 +1861,13 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
 		ca->discard = CACHE_DISCARD(&ca->sb);
 
 	ret = cache_alloc(ca);
-	if (ret != 0)
+	if (ret != 0) {
+		if (ret == -ENOMEM)
+			err = "cache_alloc(): -ENOMEM";
+		else
+			err = "cache_alloc(): unknown error";
 		goto err;
+	}
 
 	if (kobject_add(&ca->kobj, &part_to_dev(bdev->bd_part)->kobj, "bcache")) {
 		err = "error calling kobject_add";