Re: kernel BUG at mm/swap_slots.c:270
- Date: Mon, 20 Mar 2017 09:25:50 +0800
- From: "Huang\, Ying" <ying.huang@xxxxxxxxx>
- Subject: Re: kernel BUG at mm/swap_slots.c:270
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:
>> ---[ 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.