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

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Date:   Mon, 19 Jul 2021 10:59:02 +0800
From:   Zhouyi Zhou <zhouzhouyi@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     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>
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359

On Mon, Jul 19, 2021 at 10:44 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Mon, Jul 19, 2021 at 10:24:18AM +0800, Zhouyi Zhou wrote:
> > Meanwhile, I examined the 5.12.17 by naked eye, and found a suspicious place
> > 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.
>
> Yes, but the caller is supposed to call put_swap_device() which
> calls rcu_read_unlock().  See commit eb085574a752.
I see, sorry for the mistake