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Date:   Sun, 18 Jul 2021 22:22:21 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Oleksandr Natalenko <oleksandr@natalenko.name>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Chris Clayton <chris2553@googlemail.com>,
        Chris Rankin <rankincj@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        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@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359
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 <2245518.LNIG0phfVR@natalenko.name>
 <6698965.kvI7vG0SvZ@natalenko.name>
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On Sun, Jul 18, 2021 at 11:03:51PM +0200, Oleksandr Natalenko wrote:
> + stable@vger.kernel.org
> 
> On neděle 18. července 2021 23:01:24 CEST Oleksandr Natalenko wrote:
> > Hello.
> > 
> > On sobota 17. července 2021 22:22:08 CEST Chris Clayton wrote:
> > > I checked the output from dmesg yesterday and found the following warning:
> > > 
> > > [Fri Jul 16 09:15:29 2021] ------------[ cut here ]------------
> > > [Fri Jul 16 09:15:29 2021] WARNING: CPU: 11 PID: 2701 at
> > > kernel/rcu/tree_plugin.h:359 rcu_note_context_switch+0x37/0x3d0 [Fri Jul

Could you run ./scripts/faddr2line vmlinux rcu_note_context_switch+0x37/0x3d0

> > > [Fri Jul 16 09:15:29 2021] Call Trace:
> > > [Fri Jul 16 09:15:29 2021]  __schedule+0x86/0x810
> > > [Fri Jul 16 09:15:29 2021]  schedule+0x40/0xe0
> > > [Fri Jul 16 09:15:29 2021]  io_schedule+0x3d/0x60
> > > [Fri Jul 16 09:15:29 2021]  wait_on_page_bit_common+0x129/0x390
> > > [Fri Jul 16 09:15:29 2021]  ? __filemap_set_wb_err+0x10/0x10
> > > [Fri Jul 16 09:15:29 2021]  __lock_page_or_retry+0x13f/0x1d0
> > > [Fri Jul 16 09:15:29 2021]  do_swap_page+0x335/0x5b0
> > > [Fri Jul 16 09:15:29 2021]  __handle_mm_fault+0x444/0xb20
> > > [Fri Jul 16 09:15:29 2021]  handle_mm_fault+0x5c/0x170

You were handling a page fault at the time.  The page you wanted was
on swap and this warning fired as a result of waiting for the page
to come back in from swap.  There are a number of warnings in that
function, so it'd be good to track down exactly which one it is.