[PATCH 2/2] panic fix for making cache device

[Dongbo Cao]

when the nbuckets of cache device is smaller than 1024, making cache device 
will trigger BUG_ON in kernel, add a condition to avoid this.

Signed-off-by: Dongbo Cao <cdb...@163.com>
---
 drivers/md/bcache/super.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 0c0f6d8f..47d122ed 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -2036,7 +2036,12 @@ static int cache_alloc(struct cache *ca)
         */
        btree_buckets = ca->sb.njournal_buckets ?: 8;
        free = roundup_pow_of_two(ca->sb.nbuckets) >> 10;
-       
+       if (!free) {
+               ret = -EPERM;
+               err = "ca->sb.nbuckets is too small";
+               goto err_free;
+       }
+
        if (!init_fifo(&ca->free[RESERVE_BTREE], btree_buckets,
                                                GFP_KERNEL)) {
                err = "ca->free[RESERVE_BTREE] alloc failed";
@@ -2102,6 +2107,7 @@ static int cache_alloc(struct cache *ca)
 err_prio_alloc:
        free_fifo(&ca->free[RESERVE_BTREE]);
 err_btree_alloc:
+err_free:
        module_put(THIS_MODULE);
        if (err)
                pr_notice("error %s: %s", ca->cache_dev_name, err);
@@ -2131,6 +2137,8 @@ static int register_cache(struct cache_sb *sb, struct 
page *sb_page,
                blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
                if (ret == -ENOMEM)
                        err = "cache_alloc(): -ENOMEM";
+               else if (ret == -EPERM)
+                       err = "cache_alloc(): cache device is too small";
                else
                        err = "cache_alloc(): unknown error";
                goto err;
-- 
2.17.1