Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Oleksandr Natalenko <oleksandr@natalenko.name>
To:     Matthew Wilcox <willy@infradead.org>,
        Miaohe Lin <linmiaohe@huawei.com>
Cc:     Boqun Feng <boqun.feng@gmail.com>,
        Zhouyi Zhou <zhouzhouyi@gmail.com>, paulmck@kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        stable@vger.kernel.org, Chris Clayton <chris2553@googlemail.com>,
        Chris Rankin <rankincj@gmail.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        rcu <rcu@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        "Huang, Ying" <ying.huang@intel.com>, gregkh@linuxfoundation.org
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359
Date:   Mon, 19 Jul 2021 13:59:20 +0200
Message-ID: <2145858.R0O0FObHBN@natalenko.name>
In-Reply-To: <8058e175-cec5-c243-6499-c1cd4e3c8605@huawei.com>
References: <c9fd1311-662c-f993-c8ef-54af036f2f78@googlemail.com> <YPVgaY6uw59Fqg5x@casper.infradead.org> <8058e175-cec5-c243-6499-c1cd4e3c8605@huawei.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On pond=C4=9Bl=C3=AD 19. =C4=8Dervence 2021 13:50:07 CEST Miaohe Lin wrote:
> On 2021/7/19 19:22, Matthew Wilcox wrote:
> > On Mon, Jul 19, 2021 at 07:12:58PM +0800, Miaohe Lin wrote:
> >> When in the commit 2799e77529c2a, we're using the percpu_ref to serial=
ize
> >> against concurrent swapoff, i.e. there's percpu_ref inside
> >> get_swap_device() instead of rcu_read_lock(). Please see commit
> >> 63d8620ecf93 ("mm/swapfile: use percpu_ref to serialize against
> >> concurrent swapoff") for detail.
> >=20
> > Oh, so this is a backport problem.  2799e77529c2 was backported without
> > its prerequisite 63d8620ecf93.  Greg, probably best to just drop
>=20
> Yes, they're posted as a patch set:
>=20
> https://lkml.kernel.org/r/20210426123316.806267-1-linmiaohe@huawei.com
>=20
> > 2799e77529c2 from all stable trees; the race described is not very
> > important (swapoff vs reading a page back from that swap device).
> > .
>=20
> The swapoff races with reading a page back from that swap device should be
> really uncommon as most users only do swapoff when the system is going to
> shutdown.
>=20
> Sorry for the trouble!

git log --oneline v5.13..v5.13.3 --author=3D"Miaohe Lin"
11ebc09e50dc mm/zswap.c: fix two bugs in zswap_writeback_entry()
95d192da198d mm/z3fold: use release_z3fold_page_locked() to release locked=
=20
z3fold page
ccb7848e2344 mm/z3fold: fix potential memory leak in z3fold_destroy_pool()
9f7229c901c1 mm/huge_memory.c: don't discard hugepage if other processes ar=
e=20
mapping it
f13259175e4f mm/huge_memory.c: add missing read-only THP checking in=20
transparent_hugepage_enabled()
afafd371e7de mm/huge_memory.c: remove dedicated macro HPAGE_CACHE_INDEX_MASK
a533a21b692f mm/shmem: fix shmem_swapin() race with swapoff
c3b39134bbd0 swap: fix do_swap_page() race with swapoff

Do you suggest reverting "mm/shmem: fix shmem_swapin() race with swapoff" a=
s=20
well?

=2D-=20
Oleksandr Natalenko (post-factum)