From: Satoru Takeuchi <satoru.takeuchi@gmail.com>

If users set a very large value to nr_rambuf_pool argument, kernel would hit
BUG() in the error route of init_rambuf_pool().

drivers/md/dm-writeboost-metadata.c:
===============================================================================
...
static int init_rambuf_pool(struct wb_device *wb)
{
        int r = 0;
        size_t i;

        wb->rambuf_pool = kmalloc(sizeof(struct rambuffer) * wb->nr_rambuf_pool,
                                  GFP_KERNEL);
        if (!wb->rambuf_pool)                   # It is true here.
                return -ENOMEM;

        wb->rambuf_cachep = kmem_cache_create("dmwb_rambuf",
                        1 << (wb->segment_size_order + SECTOR_SHIFT),
                        1 << (wb->segment_size_order + SECTOR_SHIFT),
                        SLAB_RED_ZONE, NULL);
        if (!wb->rambuf_cachep) {
                r = -ENOMEM;                    # Enter this route or ....
                goto bad_cachep;
        }

        for (i = 0; i < wb->nr_rambuf_pool; i++) {
                size_t j;
                struct rambuffer *rambuf = wb->rambuf_pool + i;

                rambuf->data = kmem_cache_alloc(wb->rambuf_cachep, GFP_KERNEL);
                if (!rambuf->data) {
                        ...                     # ... enter this route.
                        goto bad_alloc_data;
                }
                check_buffer_alignment(rambuf->data);
        }

        return r;

bad_alloc_data:
        kmem_cache_destroy(wb->rambuf_cachep);
bad_cachep:
        kfree(wb->rambuf_pool);
        BUG();                                  # Kernel panic happens here.
        return r;
}
...
===============================================================================

Probably this BUG() was introduced erroneously and is safe to remove.

Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Cc: Joe Thornber <ejt@redhat.com>
Cc: Akira Hayakawa <ruby.wktk@gmail.com>