From: Yang Shi <shy828301@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: syzbot <syzbot+1f52b3a18d5633fa7f82@syzkaller.appspotmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alistair Popple <apopple@nvidia.com>,
chinwen.chang@mediatek.com, fgheet255t@gmail.com,
Jann Horn <jannh@google.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>, Peter Xu <peterx@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
syzkaller-bugs@googlegroups.com, tonymarislogistics@yandex.com,
Vlastimil Babka <vbabka@suse.cz>, Zi Yan <ziy@nvidia.com>
Subject: Re: [syzbot] kernel BUG in __page_mapcount
Date: Tue, 21 Dec 2021 17:42:50 -0800 [thread overview]
Message-ID: <CAHbLzkpj8tKykWfOUkffsnc7SXn395e67HVH+ys7cQ19aw-fPg@mail.gmail.com> (raw)
In-Reply-To: <CAHbLzkqYhtYNRs83DP-Cgti8-4kZn-iXHTdkesK+=U3d3N0U+w@mail.gmail.com>
On Tue, Dec 21, 2021 at 11:07 AM Yang Shi <shy828301@gmail.com> wrote:
>
> On Tue, Dec 21, 2021 at 10:40 AM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Tue, Dec 21, 2021 at 10:24:27AM -0800, Yang Shi wrote:
> > > It seems the THP is split during smaps walk. The reproducer does call
> > > MADV_FREE on partial THP which may split the huge page.
> > >
> > > The below fix (untested) should be able to fix it.
> >
> > Did you read the rest of the thread on this? If the page is being
> > migrated, we should still account it ... also, you've changed the
>
> Yes, the being migrated pages may be skipped. We should be able to add
> a new flag to smaps_account() to indicate this is a migration entry
> then don't elevate the page count.
It seems not that straightforward. THP split converts PTEs to
migration entries too. So we can't tell if it is real migration or
just in the middle of THP split.
We just need to serialize against THP split for PTE mapped subpages.
So in real life workload it might be ok to skip accounting migration
pages? Typically the migration is a transient state, so the under
accounting should be transient too. Or account migration pages
separately, just like swap entries?
I may revisit this after the holiday. If you have any better ideas,
please feel free to propose.
>
> > refcount, so this:
> >
> > if (page_count(page) == 1) {
> > smaps_page_accumulate(mss, page, size, size << PSS_SHIFT, dirty,
> > locked, true);
> > return;
> > }
> >
> > will never trigger.
>
> The get_page_unless_zero() is called after this block.
next prev parent reply other threads:[~2021-12-22 1:43 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-31 0:53 [syzbot] kernel BUG in __page_mapcount syzbot
2021-06-07 17:27 ` split_huge_page_to_list() races with page_mapcount() on migration entry in smaps code? [was: Re: [syzbot] kernel BUG in __page_mapcount] Jann Horn
2021-06-07 18:03 ` Matthew Wilcox
2021-06-07 19:55 ` Jann Horn
2021-06-07 20:20 ` Matthew Wilcox
2021-06-07 20:49 ` Kirill A. Shutemov
2021-12-21 17:24 ` [syzbot] kernel BUG in __page_mapcount syzbot
2021-12-21 18:24 ` Yang Shi
2021-12-21 18:40 ` Matthew Wilcox
2021-12-21 19:07 ` Yang Shi
2021-12-22 1:42 ` Yang Shi [this message]
2022-01-05 19:05 ` Yang Shi
2022-01-11 23:14 ` Yang Shi
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=CAHbLzkpj8tKykWfOUkffsnc7SXn395e67HVH+ys7cQ19aw-fPg@mail.gmail.com \
--to=shy828301@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=apopple@nvidia.com \
--cc=chinwen.chang@mediatek.com \
--cc=fgheet255t@gmail.com \
--cc=jannh@google.com \
--cc=khlebnikov@yandex-team.ru \
--cc=kirill.shutemov@linux.intel.com \
--cc=kirill@shutemov.name \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=peterx@redhat.com \
--cc=peterz@infradead.org \
--cc=syzbot+1f52b3a18d5633fa7f82@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tonymarislogistics@yandex.com \
--cc=vbabka@suse.cz \
--cc=willy@infradead.org \
--cc=ziy@nvidia.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.