bcache: register_bcache(): call blkdev_put() when cache_alloc() fails

commit d9dc1702b297ec4a6bb9c0326a70641b322ba886 upstream.

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.

Signed-off-by: Eric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 3b260c67db751d56ccea52f5197daa1930b7832c..267a3dec7c69a6ad72aeaa1aa1bfed0eafb40591 100644 (file)
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1854,7 +1854,7 @@ 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));
@@ -1871,8 +1871,13 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
                ca->discard = CACHE_DISCARD(&ca->sb);
 
        ret = cache_alloc(sb, 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";