lkml.org 
[lkml]   [2017]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC PATCH] mm: kasan: suppress soft lockup in slub when !CONFIG_PREEMPT
From
Date


On 12/8/17 1:16 AM, Andrey Ryabinin wrote:
> On 12/08/2017 11:26 AM, Dmitry Vyukov wrote:
>> On Fri, Dec 8, 2017 at 12:40 AM, Matthew Wilcox <willy@infradead.org> wrote:
>>> On Fri, Dec 08, 2017 at 07:30:07AM +0800, Yang Shi wrote:
>>>> When running stress test with KASAN enabled, the below softlockup may
>>>> happen occasionally:
>>>>
>>>> NMI watchdog: BUG: soft lockup - CPU#7 stuck for 22s!
>>>> hardirqs last enabled at (0): [< (null)>] (null)
>>>> hardirqs last disabled at (0): [] copy_process.part.30+0x5c6/0x1f50
>>>> softirqs last enabled at (0): [] copy_process.part.30+0x5c6/0x1f50
>>>> softirqs last disabled at (0): [< (null)>] (null)
>>>
>>>> Call Trace:
>>>> [] __slab_free+0x19c/0x270
>>>> [] ___cache_free+0xa6/0xb0
>>>> [] qlist_free_all+0x47/0x80
>>>> [] quarantine_reduce+0x159/0x190
>>>> [] kasan_kmalloc+0xaf/0xc0
>>>> [] kasan_slab_alloc+0x12/0x20
>>>> [] kmem_cache_alloc+0xfa/0x360
>>>> [] ? getname_flags+0x4f/0x1f0
>>>> [] getname_flags+0x4f/0x1f0
>>>> [] getname+0x12/0x20
>>>> [] do_sys_open+0xf9/0x210
>>>> [] SyS_open+0x1e/0x20
>>>> [] entry_SYSCALL_64_fastpath+0x1f/0xc2
>>>
>>> This feels like papering over a problem. KASAN only calls
>>> quarantine_reduce() when it's allowed to block. Presumably it has
>>> millions of entries on the free list at this point. I think the right
>>> thing to do is for qlist_free_all() to call cond_resched() after freeing
>>> every N items.
>>
>>
>> Agree. Adding touch_softlockup_watchdog() to a random low-level
>> function looks like a wrong thing to do.
>> quarantine_reduce() already has this logic. Look at
>> QUARANTINE_BATCHES. It's meant to do exactly this -- limit amount of
>> work in quarantine_reduce() and in quarantine_remove_cache() to
>> reasonably-sized batches. We could simply increase number of batches
>> to make them smaller. But it would be good to understand what exactly
>> happens in this case. Batches should on a par of ~~1MB. Why freeing
>> 1MB worth of objects (smallest of which is 32b) takes 22 seconds?
>>
>
> I think the problem here is that kernel 4.9.44-003.ali3000.alios7.x86_64.debug
> doesn't have 64abdcb24351 ("kasan: eliminate long stalls during quarantine reduction").
>
> We probably should ask that commit to be included in stable, but it would be good to hear
> a confirmation from Yang that it really helps.

Thanks, folks. Yes, my kernel doesn't have this commit. It sounds the
commit batches the quarantine to smaller group. I will run some tests
against this commit to see if it could help. Reading the code tells me
it is likely to help.

Yang

>

\
 
 \ /
  Last update: 2017-12-11 19:00    [W:0.284 / U:0.488 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site