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

torvalds · torvalds · commit 452b94b8c8c7 · 2017-03-19T19:00:47.000-07:00
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" &lt;ying.huang@intel.com&gt;
Cc: Tim Chen &lt;tim.c.chen@linux.intel.com&gt;
Cc: Michal Hocko &lt;mhocko@suse.com&gt;
Cc: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
diff --git 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) {

Original file line number	Diff line number	Diff line change
`@@ -267,7 +267,7 @@ int free_swap_slot(swp_entry_t entry)`
`267`	`267`	`{`
`268`	`268`	`struct swap_slots_cache *cache;`
`269`	`269`
`270`		`- BUG_ON(!swap_slot_cache_initialized);`
	`270`	`+ WARN_ON_ONCE(!swap_slot_cache_initialized);`
`271`	`271`
`272`	`272`	`cache = &get_cpu_var(swp_slots);`
`273`	`273`	`if (use_swap_slot_cache && cache->slots_ret) {`