From: Wei Yang <richardw.yang@linux.intel.com>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Wei Yang <richardw.yang@linux.intel.com>,
Shakeel Butt <shakeelb@google.com>, Qian Cai <cai@lca.pw>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@surriel.com>, Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
linux-s390@vger.kernel.org
Subject: Re: "reuse mergeable anon_vma as parent when fork" causes a crash on s390
Date: Thu, 10 Oct 2019 22:03:49 +0800 [thread overview]
Message-ID: <20191010140349.GA28204@richard> (raw)
In-Reply-To: <8e0d9999-9ee3-78e5-2737-5a504243413c@yandex-team.ru>
On Thu, Oct 10, 2019 at 11:29:44AM +0300, Konstantin Khlebnikov wrote:
>On 10/10/2019 06.15, Wei Yang wrote:
>> On Thu, Oct 10, 2019 at 10:36:01AM +0800, Wei Yang wrote:
>> > Hi, Qian, Shakeel
>> >
>> > Thanks for testing.
>> >
>> > Sounds I missed some case to handle. anon_vma_clone() now would be called in
>> > vma_adjust, which is a different case when it is introduced.
>> >
>>
>> Well, I have to correct my statement. The reason is we may did something more
>> in anon_vma_clone().
>>
>> Here is a quick fix, while I need to go through all the cases carefully.
>
>Oops, I've overlooked this case too.
>
>You have to check src->anon_vma
>otherwise in __split_vma or copy_vma dst could pick completely random anon_vma.
>
Per my understanding, the root cause is commit 7a3ef208e662 did a little
further for the reuse case.
We intend to reuse anon_vma on fork, but we also did this when we just want a
copy of src, like __split_vma(), copy_vma() and __vma_split(). This will lead
to a random anon_vma and not what we expect.
A fix patch is sent for this.
>Also checking prev will not hurt, just to be sure.
>
>So, something like this should work:
>
>if (!dst->anon_vma && src->anon_vma &&
> prev && pprev && pprev->anon_vma == src->anon_vma)
> dst->anon_vma = prev->anon_vma;
>
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 12f6c3d7fd9d..2844f442208d 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -271,7 +271,7 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
>> * 1. Parent has vm_prev, which implies we have vm_prev.
>> * 2. Parent and its vm_prev have the same anon_vma.
>> */
>> - if (pprev && pprev->anon_vma == src->anon_vma)
>> + if (!dst->anon_vma && pprev && pprev->anon_vma == src->anon_vma)
>> dst->anon_vma = prev->anon_vma;
>> list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
>>
>> > BTW, do you have the specific test case? So that I could verify my change. The
>> > kernel build test doesn't trigger this.
>> >
>> > Thanks a lot :-)
>> >
>> > On Wed, Oct 09, 2019 at 03:21:11PM -0700, Shakeel Butt wrote:
>> > --
>> > Wei Yang
>> > Help you, Help me
>>
--
Wei Yang
Help you, Help me
prev parent reply other threads:[~2019-10-10 14:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 21:29 "reuse mergeable anon_vma as parent when fork" causes a crash on s390 Qian Cai
2019-10-09 22:21 ` Shakeel Butt
2019-10-10 0:04 ` Andrew Morton
2019-10-10 2:36 ` Wei Yang
2019-10-10 3:15 ` Wei Yang
2019-10-10 8:29 ` Konstantin Khlebnikov
2019-10-10 12:14 ` Wei Yang
2019-10-10 14:03 ` Wei Yang [this message]
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