From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BCEEC4CECE for ; Mon, 14 Oct 2019 22:40:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 046B121848 for ; Mon, 14 Oct 2019 22:40:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="QpY6UwJM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 046B121848 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 934238E0005; Mon, 14 Oct 2019 18:40:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8E35B8E0001; Mon, 14 Oct 2019 18:40:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7AB048E0005; Mon, 14 Oct 2019 18:40:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0193.hostedemail.com [216.40.44.193]) by kanga.kvack.org (Postfix) with ESMTP id 58FF68E0001 for ; Mon, 14 Oct 2019 18:40:32 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id DD4AC181AEF30 for ; Mon, 14 Oct 2019 22:40:31 +0000 (UTC) X-FDA: 76043860662.24.songs37_78fcb9819be39 X-HE-Tag: songs37_78fcb9819be39 X-Filterd-Recvd-Size: 5637 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Mon, 14 Oct 2019 22:40:31 +0000 (UTC) Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C3A2221835; Mon, 14 Oct 2019 22:40:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571092830; bh=F+BvU2ynT3mQL45LYq/lwNf6fNbzXrmBPj+eP1A4W2E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QpY6UwJMG2+5bzwrvASfxt8y8zxJ/F1VKC1nAtFH1wmDywJZUvo9iasZnlNdvdV7w S+IZUMEh35OE5VpJTmdOY4TawLghWweKIX/DD/5zwZr9rVhlU3HD9PODVzP+7XMwLn MSvAZNxUfOXraehJI6/nK5bwH0S86MqNa2iTvszs= Date: Mon, 14 Oct 2019 15:40:29 -0700 From: Andrew Morton To: syzbot Cc: chenjianhong2@huawei.com, jannh@google.com, khlebnikov@yandex-team.ru, kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, mike.kravetz@oracle.com, richardw.yang@linux.intel.com, riel@surriel.com, sfr@canb.auug.org.au, steve.capper@arm.com, syzkaller-bugs@googlegroups.com, tiny.windzz@gmail.com, vbabka@suse.cz, walken@google.com, willy@infradead.org, yang.shi@linux.alibaba.com Subject: Re: kernel BUG at include/linux/rmap.h:LINE! Message-Id: <20191014154029.ab909c9bf08c78bbc2404f2d@linux-foundation.org> In-Reply-To: <000000000000683a810594d634a2@google.com> References: <000000000000683a810594d634a2@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, 13 Oct 2019 20:10:06 -0700 syzbot wrote: > syzbot found the following crash on: >=20 > HEAD commit: 442630f6 Add linux-next specific files for 20191008 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=3D11450d93600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=3Daf1bfeef713ee= fdd > dashboard link: https://syzkaller.appspot.com/bug?extid=3D3370fc9fb190f98= c5c72 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=3D13132d57600= 000 >=20 > The bug was bisected to: >=20 > commit 480706f51e2c3a450d2f7fc10f5af215c9d249df > Author: Wei Yang > Date: Mon Oct 7 20:25:37 2019 +0000 >=20 > mm/rmap.c: reuse mergeable anon_vma as parent when forking Hopefully the updated version addresses this? From: Wei Yang Subject: mm/rmap.c: reuse mergeable anon_vma as parent when fork In __anon_vma_prepare(), we will try to find anon_vma if it is possible to reuse it. While on fork, the logic is different. Since commit 5beb49305251 ("mm: change anon_vma linking to fix multi-process server scalability issue"), function anon_vma_clone() tries to allocate new anon_vma for child process. But the logic here will allocate a new anon_vma for each vma, even in parent this vma is mergeable and share the same anon_vma with its sibling. This may do better for scalability issue, while it is not necessary to do so especially after interval tree is used. Commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy") tries to reuse some anon_vma by counting child anon_vma and attached vmas. While for those mergeable anon_vmas, we can just reuse it and not necessary to go through the logic. After this change, kernel build test reduces 20% anon_vma allocation. Do the same kernel build test, it shows run time in sys reduced 11.6%. Origin: real 2m50.467s user 17m52.002s sys 1m51.953s real 2m48.662s user 17m55.464s sys 1m50.553s real 2m51.143s user 17m59.687s sys 1m53.600s Patched: real 2m39.933s user 17m1.835s sys 1m38.802s real 2m39.321s user 17m1.634s sys 1m39.206s real 2m39.575s user 17m1.420s sys 1m38.845s Link: http://lkml.kernel.org/r/20191011072256.16275-2-richardw.yang@linux.i= ntel.com Signed-off-by: Wei Yang Acked-by: Konstantin Khlebnikov Cc: Kirill A. Shutemov Cc: "J=E9r=F4me Glisse" Cc: Mike Kravetz Cc: Rik van Riel Cc: Qian Cai Cc: Shakeel Butt Signed-off-by: Andrew Morton --- mm/rmap.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) --- a/mm/rmap.c~mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork +++ a/mm/rmap.c @@ -268,6 +268,19 @@ int anon_vma_clone(struct vm_area_struct { struct anon_vma_chain *avc, *pavc; struct anon_vma *root =3D NULL; + struct vm_area_struct *prev =3D dst->vm_prev, *pprev =3D src->vm_prev; + + /* + * If parent share anon_vma with its vm_prev, keep this sharing in in + * child. + * + * 1. Parent has vm_prev, which implies we have vm_prev. + * 2. Parent and its vm_prev have the same anon_vma. + */ + if (!dst->anon_vma && src->anon_vma && + pprev && pprev->anon_vma =3D=3D src->anon_vma) + dst->anon_vma =3D prev->anon_vma; + =20 list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) { struct anon_vma *anon_vma; _