From: Andrew Morton <akpm@linux-foundation.org>
To: syzbot <syzbot+3370fc9fb190f98c5c72@syzkaller.appspotmail.com>
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!
Date: Mon, 14 Oct 2019 15:40:29 -0700 [thread overview]
Message-ID: <20191014154029.ab909c9bf08c78bbc2404f2d@linux-foundation.org> (raw)
In-Reply-To: <000000000000683a810594d634a2@google.com>
On Sun, 13 Oct 2019 20:10:06 -0700 syzbot <syzbot+3370fc9fb190f98c5c72@syzkaller.appspotmail.com> wrote:
> syzbot found the following crash on:
>
> HEAD commit: 442630f6 Add linux-next specific files for 20191008
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=11450d93600000
> kernel config: https://syzkaller.appspot.com/x/.config?x=af1bfeef713eefdd
> dashboard link: https://syzkaller.appspot.com/bug?extid=3370fc9fb190f98c5c72
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13132d57600000
>
> The bug was bisected to:
>
> commit 480706f51e2c3a450d2f7fc10f5af215c9d249df
> Author: Wei Yang <richardw.yang@linux.intel.com>
> Date: Mon Oct 7 20:25:37 2019 +0000
>
> mm/rmap.c: reuse mergeable anon_vma as parent when forking
Hopefully the updated version addresses this?
From: Wei Yang <richardw.yang@linux.intel.com>
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.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
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 = NULL;
+ struct vm_area_struct *prev = dst->vm_prev, *pprev = 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 == src->anon_vma)
+ dst->anon_vma = prev->anon_vma;
+
list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
_
prev parent reply other threads:[~2019-10-14 22:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-14 3:10 kernel BUG at include/linux/rmap.h:LINE! syzbot
2019-10-14 22:40 ` Andrew Morton [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191014154029.ab909c9bf08c78bbc2404f2d@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=chenjianhong2@huawei.com \
--cc=jannh@google.com \
--cc=khlebnikov@yandex-team.ru \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=mike.kravetz@oracle.com \
--cc=richardw.yang@linux.intel.com \
--cc=riel@surriel.com \
--cc=sfr@canb.auug.org.au \
--cc=steve.capper@arm.com \
--cc=syzbot+3370fc9fb190f98c5c72@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tiny.windzz@gmail.com \
--cc=vbabka@suse.cz \
--cc=walken@google.com \
--cc=willy@infradead.org \
--cc=yang.shi@linux.alibaba.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).