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Subject[PATCH 3.16 192/346] bcache: register_bcache(): call blkdev_put() when cache_alloc() fails
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Wheeler <git@linux.ewheeler.net>

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>
---
drivers/md/bcache/super.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1854,7 +1854,7 @@ static int register_cache(struct cache_s
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_s
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";
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