Re: kernel BUG at mm/swap_slots.c:270
- Date: Sun, 19 Mar 2017 10:04:47 -0400
- From: Michal Hocko <mhocko@xxxxxxxxxx>
- Subject: Re: kernel BUG at mm/swap_slots.c:270
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:
> ---[ 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.