Subject: Re: [PATCH v4 29/33] x86/mm: try VMA lock-based page fault handling first

From: Jiri Slaby <[email-masked]>
Date: Mon, 3 Jul 2023 12:47:33 +0200

Cc Jacob Young (from kernel bugzilla)

On 30. 06. 23, 19:40, Suren Baghdasaryan wrote:
> On Fri, Jun 30, 2023 at 1:43 AM Jiri Slaby <[email-masked]> wrote:
>>
>> On 30. 06. 23, 10:28, Jiri Slaby wrote:
>>>   > 2348
>>> clone3({flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, child_tid=0x7fcaa5882990, parent_tid=0x7fcaa5882990, exit_signal=0, stack=0x7fcaa5082000, stack_size=0x7ffe00, tls=0x7fcaa58826c0} => {parent_tid=[2351]}, 88) = 2351
>>>   > 2350  <... clone3 resumed> => {parent_tid=[2372]}, 88) = 2372
>>>   > 2351  <... clone3 resumed> => {parent_tid=[2354]}, 88) = 2354
>>>   > 2351  <... clone3 resumed> => {parent_tid=[2357]}, 88) = 2357
>>>   > 2354  <... clone3 resumed> => {parent_tid=[2355]}, 88) = 2355
>>>   > 2355  <... clone3 resumed> => {parent_tid=[2370]}, 88) = 2370
>>>   > 2370  mmap(NULL, 262144, PROT_READ|PROT_WRITE,
>>> MAP_PRIVATE|MAP_ANONYMOUS, -1, 0 <unfinished ...>
>>>   > 2370  <... mmap resumed>)               = 0x7fca68249000
>>>   > 2372  <... clone3 resumed> => {parent_tid=[2384]}, 88) = 2384
>>>   > 2384  <... clone3 resumed> => {parent_tid=[2388]}, 88) = 2388
>>>   > 2388  <... clone3 resumed> => {parent_tid=[2392]}, 88) = 2392
>>>   > 2392  <... clone3 resumed> => {parent_tid=[2395]}, 88) = 2395
>>>   > 2395  write(2, "runtime: marked free object in s"..., 36 <unfinished
>>> ...>
>>>
>>> I.e. IIUC, all are threads (CLONE_VM) and thread 2370 mapped ANON
>>> 0x7fca68249000 - 0x7fca6827ffff and go in thread 2395 thinks for some
>>> reason 0x7fca6824bec8 in that region is "bad".
> 
> Thanks for the analysis Jiri.
> Is it possible from these logs to identify whether 2370 finished the
> mmap operation before 2395 tried to access 0x7fca6824bec8? That access
> has to happen only after mmap finishes mapping the region.

Hi,

it's hard to tell, but I assume so.

For now, forget about this go's overly complicated, hard to reproduce 
case and concentrate on the very nice reduced testcase in:
  https://bugzilla.kernel.org/show_bug.cgi?id=217624
;)

FWIW, I can reproduce using the test case too.

thanks,
-- 
js
suse labs