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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YPVQfaamqwu1PRrK@boqun-archlinux>
Date:   Mon, 19 Jul 2021 18:14:21 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     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>, Miaohe Lin <linmiaohe@...wei.com>,
        "Huang, Ying" <ying.huang@...el.com>
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359

On Mon, Jul 19, 2021 at 03:43:00AM +0100, Matthew Wilcox 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.

Right, but we need to make sure there is no sleepable function called
before put_swap_device() called, and the call trace showed the following
happened:

	do_swap_page():
	  si = get_swap_device():
	    rcu_read_lock();
	  lock_page_or_retry():
	    might_sleep(); // call a sleepable function inside RCU read-side c.s.
	    __lock_page_or_retry():
	      wait_on_page_bit_common():
	        schedule():
		  rcu_note_context_switch();
		  // Warn here
	  put_swap_device();
	    rcu_read_unlock();

, which introduced by commit 2799e77529c2a

[Copy the author]

Regards,
Boqun