mm/swap: don't BUG_ON() due to uninitialized swap slot cache

This BUG_ON() triggered for me once at shutdown, and I don't see a
reason for the check.  The code correctly checks whether the swap slot
cache is usable or not, so an uninitialized swap slot cache is not
actually problematic afaik.

I've temporarily just switched the BUG_ON() to a WARN_ON_ONCE(), since
I'm not sure why that seemingly pointless check was there.  I suspect
the real fix is to just remove it entirely, but for now we'll warn about
it but not bring the machine down.

Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 9b5bc86f96ad731269e2051719583f168a74bc51..7ebb23836f689e766caa71bd775c0b919f658bb9 100644 (file)
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -267,7 +267,7 @@ int free_swap_slot(swp_entry_t entry)
 {
        struct swap_slots_cache *cache;
 
-       BUG_ON(!swap_slot_cache_initialized);
+       WARN_ON_ONCE(!swap_slot_cache_initialized);
 
        cache = &get_cpu_var(swp_slots);
        if (use_swap_slot_cache && cache->slots_ret) {