linux-kernel - Re: linux-5.13.2: warning from kernel/rcu/tree

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Message-ID: <YPVgaY6uw59Fqg5x@casper.infradead.org>
Date:   Mon, 19 Jul 2021 12:22:17 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        Zhouyi Zhou <zhouzhouyi@...il.com>, paulmck@...nel.org,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Chris Clayton <chris2553@...glemail.com>,
        Chris Rankin <rankincj@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        rcu <rcu@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        "Huang, Ying" <ying.huang@...el.com>, gregkh@...uxfoundation.org
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359

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 serialize 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.

Oh, so this is a backport problem.  2799e77529c2 was backported without
its prerequisite 63d8620ecf93.  Greg, probably best to just drop
2799e77529c2 from all stable trees; the race described is not very
important (swapoff vs reading a page back from that swap device).