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@xxxxxxxxxxxxx> 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
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