On Mon, Mar 20, 2017 at 09:25:50AM +0800, Huang, Ying wrote: > Hi, > > Michal Hocko <mhocko@xxxxxxxxxx> writes: > > > On Sat 18-03-17 09:57:18, Linus Torvalds wrote: > >> Tim at al, > >> I got this on my desktop at shutdown: > >> > >> ------------[ 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 ]--- > >> > >> so there seems to be something screwy in the new swap_slots code. > > > > I am travelling (LSFMM) so I didn't get to look at this more thoroughly > > but it seems like a race because enable_swap_slots_cache is called at > > the very end of the swapon and we could have already created a swap > > entry for a page by that time I guess. > > > >> Any ideas? I'm not finding other reports of this, but I'm also not > >> seeing why it should BUG_ON(). The "use_swap_slot_cache" thing very > >> much checks whether swap_slot_cache_initialized has been set, so the > >> BUG_ON() just seems like garbage. But please take a look. > > > > I guess you are right. I cannot speak of the original intention but it > > seems Tim wanted to be careful to not see unexpected swap entry when > > the swap wasn't initialized yet. I would just drop the BUG_ON and bail > > out when the slot cache hasn't been initialized yet. > > Yes. The BUG_ON() is problematic. The initialization of swap slot > cache may fail too, if so, we should still allow using swap without slot > cache. Will send out a fixing patch ASAP. > I kind of suspect that the swap slot cache initialization failed for some reason. But swap should still work when we try to free a swap slot without the slots cache. A proposed patch to fix this problem: --->8--- From: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> Date: Mon, 20 Mar 2017 10:00:03 -0400 Subject: [PATCH] mm/swap: Fix inappropriate BUG_ON in swap_slots.c It is possible that we don't have swap_slots cache configured and running when swap is in use and swap slot is freed. So the BUG_ON is in appropriate when swap_slots cache is not initizliaed when a swap slot is released. Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> --- mm/swap_slots.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/swap_slots.c b/mm/swap_slots.c index 9b5bc86..a17ecbf 100644 --- a/mm/swap_slots.c +++ b/mm/swap_slots.c @@ -267,10 +267,11 @@ int free_swap_slot(swp_entry_t entry) { struct swap_slots_cache *cache; - BUG_ON(!swap_slot_cache_initialized); + if (unlikely(!use_swap_slot_cache)) + swapcache_free_entries(&entry, 1); cache = &get_cpu_var(swp_slots); - if (use_swap_slot_cache && cache->slots_ret) { + if (cache->slots_ret) { spin_lock_irq(&cache->free_lock); /* Swap slots cache may be deactivated before acquiring lock */ if (!use_swap_slot_cache) { -- 2.5.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>