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Subject: Re: linux-next test error: BUG: using __this_cpu_read() in
 preemptible code in __mod_memcg_state
From:   Alex Shi <alex.shi@linux.alibaba.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        syzbot <syzbot+826543256ed3b8c37f62@syzkaller.appspotmail.com>
Cc:     akpm@linux-foundation.org, cgroups@vger.kernel.org,
        hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, mhocko@kernel.org,
        syzkaller-bugs@googlegroups.com, vdavydov.dev@gmail.com
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Message-ID: <d3fb0593-e483-3b69-bf2c-99ad6cd03567@linux.alibaba.com>
Date:   Mon, 9 Mar 2020 21:26:59 +0800
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?? 2020/3/9 ????5:56, Alex Shi д??:
> 
> 
> ?? 2020/3/9 ????5:24, Kirill A. Shutemov д??:
>>> check_preemption_disabled: 3 callbacks suppressed
>>> BUG: using __this_cpu_read() in preemptible [00000000] code: syz-fuzzer/9432
>>> caller is __mod_memcg_state+0x27/0x1a0 mm/memcontrol.c:689
>>> CPU: 1 PID: 9432 Comm: syz-fuzzer Not tainted 5.6.0-rc4-next-20200306-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>> Call Trace:
>>>  __dump_stack lib/dump_stack.c:77 [inline]
>>>  dump_stack+0x188/0x20d lib/dump_stack.c:118
>>>  check_preemption_disabled lib/smp_processor_id.c:47 [inline]
>>>  __this_cpu_preempt_check.cold+0x84/0x90 lib/smp_processor_id.c:64
>>>  __mod_memcg_state+0x27/0x1a0 mm/memcontrol.c:689
>>>  __split_huge_page mm/huge_memory.c:2575 [inline]
>>>  split_huge_page_to_list+0x124b/0x3380 mm/huge_memory.c:2862
>>>  split_huge_page include/linux/huge_mm.h:167 [inline]
>> It looks like a regression due to c8cba0cc2a80 ("mm/thp: narrow lru
>> locking").
> 
> yes, I guess so.

Yes, it is a stupid mistake to pull out lock for __mod_memcg_state which
should be in a lock.

revert this patch should be all fine, since ClearPageCompound and page_ref_inc
later may related with lru_list valid issue in release_pges.


Sorry for the disaster!

Alex