From: Zhouyi Zhou <zhouzhouyi@gmail.com>
To: paulmck@kernel.org
Cc: Matthew Wilcox <willy@infradead.org>,
Oleksandr Natalenko <oleksandr@natalenko.name>,
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>
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359
Date: Mon, 19 Jul 2021 10:27:43 +0800 [thread overview]
Message-ID: <CAABZP2yrK-Jqg2m8zWrBbRTMk7wF4dfwG=Dou_qCDDpgB9XBqA@mail.gmail.com> (raw)
In-Reply-To: <CAABZP2yE+3vzd+LgJDJcJ2f8qttJQSUQ6efD9MaFd2iD4xPTZA@mail.gmail.com>
On Mon, Jul 19, 2021 at 10:24 AM Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>
> On Mon, Jul 19, 2021 at 9:53 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Sun, Jul 18, 2021 at 11:51:36PM +0100, Matthew Wilcox wrote:
> > > On Sun, Jul 18, 2021 at 02:59:14PM -0700, Paul E. McKenney wrote:
> > > > > > https://lore.kernel.org/lkml/CAK2bqVK0Q9YcpakE7_Rc6nr-E4e2GnMOgi5jJj=_Eh_1k
> > > > > > EHLHA@mail.gmail.com/
> > > >
> > > > But this one does show this warning in v5.12.17:
> > > >
> > > > WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
> > > >
> > > > This is in rcu_note_context_switch(), and could be caused by something
> > > > like a schedule() within an RCU read-side critical section. This would
> > > > of course be RCU-usage bugs, given that you are not permitted to block
> > > > within an RCU read-side critical section.
> > > >
> > > > I suggest checking the functions in the stack trace to see where the
> > > > rcu_read_lock() is hiding. CONFIG_PROVE_LOCKING might also be helpful.
> > >
> > > I'm not sure I see it in this stack trace.
> > >
> > > Is it possible that there's something taking the rcu read lock in an
> > > interrupt handler, then returning from the interrupt handler without
> > > releasing the rcu lock? Do we have debugging that would fire if
> > > somebody did this?
> >
> > Lockdep should complain, but in the absence of lockdep I don't know
> > that anything would gripe in this situation.
> I think Lockdep should complain.
> Meanwhile, I examined the 5.12.17 by naked eye, and found a suspicious place
I examined 5.13.2 the unpaired rcu_read_lock is still there
> that could possibly trigger that problem:
>
> struct swap_info_struct *get_swap_device(swp_entry_t entry)
> {
> struct swap_info_struct *si;
> unsigned long offset;
>
> if (!entry.val)
> goto out;
> si = swp_swap_info(entry);
> if (!si)
> goto bad_nofile;
>
> rcu_read_lock();
> if (data_race(!(si->flags & SWP_VALID)))
> goto unlock_out;
> offset = swp_offset(entry);
> if (offset >= si->max)
> goto unlock_out;
>
> return si;
> bad_nofile:
> pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
> out:
> return NULL;
> unlock_out:
> rcu_read_unlock();
> return NULL;
> }
> I guess the function "return si" without a rcu_read_unlock.
>
> However the get_swap_device has changed in the mainline tree,
> there is no rcu_read_lock anymore.
>
> >
> > Also, this is a preemptible kernel, so it is possible to trace
> > __rcu_read_lock(), if that helps.
> >
> > Thanx, Paul
> Thanx
> Zhouyi
next prev parent reply other threads:[~2021-07-19 2:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <c9fd1311-662c-f993-c8ef-54af036f2f78@googlemail.com>
2021-07-18 21:01 ` linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359 Oleksandr Natalenko
2021-07-18 21:03 ` Oleksandr Natalenko
2021-07-18 21:22 ` Matthew Wilcox
2021-07-18 21:36 ` Chris Clayton
2021-07-18 21:59 ` Paul E. McKenney
2021-07-18 22:51 ` Matthew Wilcox
2021-07-19 1:53 ` Paul E. McKenney
2021-07-19 2:24 ` Zhouyi Zhou
2021-07-19 2:27 ` Zhouyi Zhou [this message]
2021-07-19 2:43 ` Matthew Wilcox
2021-07-19 2:59 ` Zhouyi Zhou
2021-07-19 10:14 ` Boqun Feng
2021-07-19 11:12 ` Miaohe Lin
2021-07-19 11:17 ` Oleksandr Natalenko
2021-07-19 11:22 ` Matthew Wilcox
2021-07-19 11:50 ` Miaohe Lin
2021-07-19 11:59 ` Oleksandr Natalenko
2021-07-19 12:08 ` Miaohe Lin
2021-07-19 12:12 ` Oleksandr Natalenko
2021-07-19 12:16 ` Matthew Wilcox
2021-07-19 12:23 ` Oleksandr Natalenko
2021-07-19 16:47 ` Zhouyi Zhou
[not found] ` <CAABZP2yh3J8+P=3PLZVaC47ymKC7PcfQCBBxjXJ9Ybn+HREbdg@mail.gmail.com>
2021-07-22 7:30 ` Chris Clayton
2021-07-22 8:57 ` Zhouyi Zhou
2021-07-22 12:36 ` Matthew Wilcox
2021-07-22 13:26 ` Greg KH
2021-07-22 14:00 ` Greg KH
2021-07-23 1:51 ` Miaohe Lin
2021-07-23 7:02 ` Greg KH
2021-07-23 7:13 ` Miaohe Lin
2021-07-22 17:44 ` Zhouyi Zhou
2021-07-22 14:05 ` Paul E. McKenney
2021-07-19 12:17 ` Miaohe Lin
2021-07-19 7:32 ` Chris Clayton
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