Hi, Michal Hocko <mho...@kernel.org> 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. Best Regards, Huang, Ying
