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Date:   Thu, 22 Jul 2021 13:36:02 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc:     Chris Clayton <chris2553@googlemail.com>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Boqun Feng <boqun.feng@gmail.com>, paulmck@kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        stable@vger.kernel.org, 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>,
        Greg KH <gregkh@linuxfoundation.org>
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359
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On Thu, Jul 22, 2021 at 04:57:57PM +0800, Zhouyi Zhou wrote:
> Thanks for reviewing,
> 
> What I have deduced from the dmesg  is:
> In function do_swap_page,
> after invoking
> 3385        si = get_swap_device(entry); /* rcu_read_lock */
> and before
> 3561    out:
> 3562        if (si)
> 3563            put_swap_device(si);
> The thread got scheduled out in
> 3454        locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
> 
> I am only familiar with Linux RCU subsystem, hope mm people can solve our
> confusions.

I don't understamd why you're still talking.  The problem is understood.
You need to revert the unnecessary backport of 2799e77529c2 and
2efa33fc7f6e