From: Huang Ying <[email protected]> Before commit 452b94b8c8c7 ("mm/swap: don't BUG_ON() due to uninitialized swap slot cache"), the following bug is reported,
------------[ cut here ]------------ kernel BUG at mm/swap_slots.c:270! invalid opcode: 0000 [#1] SMP CPU: 5 PID: 1745 Comm: (sd-pam) Not tainted 4.11.0-rc1-00243-g24c534bb161b #1 Hardware name: System manufacturer System Product Name/Z170-K, BIOS 1803 05/06/2016 RIP: 0010:free_swap_slot+0xba/0xd0 Call Trace: swap_free+0x36/0x40 do_swap_page+0x360/0x6d0 __handle_mm_fault+0x880/0x1080 handle_mm_fault+0xd0/0x240 __do_page_fault+0x232/0x4d0 do_page_fault+0x20/0x70 page_fault+0x22/0x30 ---[ end trace aefc9ede53e0ab21 ]--- This is raised by the BUG_ON(!swap_slot_cache_initialized) in free_swap_slot(). This is incorrect, because even if the swap slots cache fails to be initialized, the swap should operate properly without the swap slots cache. And the use_swap_slot_cache check later in the function will protect the uninitialized swap slots cache case. In commit 452b94b8c8c7, the BUG_ON() is replaced by WARN_ON_ONCE(). In the patch, the WARN_ON_ONCE() is removed too. Reported-by: Linus Torvalds <[email protected]> Cc: Tim Chen <[email protected]> Cc: Michal Hocko <[email protected]> Signed-off-by: "Huang, Ying" <[email protected]> --- mm/swap_slots.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/mm/swap_slots.c b/mm/swap_slots.c index 7ebb23836f68..b1ccb58ad397 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -267,8 +267,6 @@ int free_swap_slot(swp_entry_t entry) { struct swap_slots_cache *cache; - WARN_ON_ONCE(!swap_slot_cache_initialized); - cache = &get_cpu_var(swp_slots); if (use_swap_slot_cache && cache->slots_ret) { spin_lock_irq(&cache->free_lock); -- 2.11.0
