From: Stephen Hemminger <shemminger@vyatta.com>
To: ebiederm@xmission.com (Eric W. Biederman)
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
Patrick McHardy <kaber@trash.net>,
Linux Netdev List <netdev@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: IPv4/IPv6 sysctl unregistration deadlock
Date: Thu, 26 Feb 2009 08:49:24 -0800 [thread overview]
Message-ID: <20090226084924.16cb3e08@nehalam> (raw)
In-Reply-To: <m14oyhis31.fsf@fess.ebiederm.org>
On Wed, 25 Feb 2009 23:18:42 -0800
ebiederm@xmission.com (Eric W. Biederman) wrote:
> Herbert Xu <herbert@gondor.apana.org.au> writes:
>
> > On Wed, Feb 25, 2009 at 10:10:33PM -0800, Eric W. Biederman wrote:
> >>
> >> How does adding a rename operation to sysctl sound?
> >
> > Yes that would definitely help. Of course for the unregister case
> > we'd still need either an async removal or a no-op as Patrick
> > suggested.
>
> After having reread the thread and looking at the code I think
> I understand what is happening.
>
> sysctl, proc, and sysfs all need to wait until there are no
> more users before their unregister operation succeeds. So that
> we can guarantee that it is safe to remove a module that provides
> the callback function.
>
> Currently ndo_stop, NETDEV_DOWN, unlist_netdevice and I don't
> know how much other code is run from unregister_netdevice
> with the rtnl lock. If we do an asynchronous unregister
> we need to ensure that entire code path is safe without
> rtnl_lock. And we would need to run the unregister work
> from rtnl_lock.
>
> Ugh. netdev_store() and a few other functions in net-sysfs.c
> take rtnl_lock. The instance in netdev_store appears to date
> back to 21 May 2003 sometime during 2.5.
>
> So this is an old problem that we are just noticing now. Ugh.
>
> Currently rtnl_lock() protects the netdevice_notifier_chain.
> So it appears we need to hold rtnl_lock().
>
> Which leads me to conclude either we need to completely rewrite the
> locking rules for the networking stack, or we need to teach the sysfs,
> sysctl, and proc how to grab a subsystem lock around a callback.
>
> We already do this for netlink with netlink_create_kernel.
>
> So I guess we need a variants of:
> register_sysctl_table, proc_create, and class_create_file.
>
> What a pain, but at least it looks like it can work.
>
> Eric
What about something like this:
Subject: [PATCH] Avoid race between network down and sysfs
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
--- a/net/core/net-sysfs.c 2009-02-26 08:36:18.000000000 -0800
+++ b/net/core/net-sysfs.c 2009-02-26 08:37:51.000000000 -0800
@@ -77,7 +77,9 @@ static ssize_t netdev_store(struct devic
if (endp == buf)
goto err;
- rtnl_lock();
+ if (!rtnl_trylock())
+ return -ERESTARTSYS;
+
if (dev_isalive(net)) {
if ((ret = (*set)(net, new)) == 0)
ret = len;
next prev parent reply other threads:[~2009-02-26 16:49 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-25 5:23 IPv4/IPv6 sysctl unregistration deadlock Patrick McHardy
2009-02-25 6:19 ` Herbert Xu
2009-02-25 6:23 ` Patrick McHardy
2009-02-25 7:18 ` Patrick McHardy
2009-02-25 8:43 ` Herbert Xu
2009-02-26 6:06 ` Eric W. Biederman
2009-02-26 6:10 ` Eric W. Biederman
2009-02-26 6:22 ` Herbert Xu
2009-02-26 7:18 ` Eric W. Biederman
2009-02-26 16:49 ` Stephen Hemminger [this message]
2009-02-26 19:01 ` Eric W. Biederman
2009-02-26 20:24 ` Stephen Hemminger
2009-02-27 0:59 ` Herbert Xu
2009-02-27 1:25 ` Stephen Hemminger
2009-02-27 18:26 ` Ben Greear
2009-02-27 18:38 ` Stephen Hemminger
2009-03-02 11:07 ` Patrick McHardy
2009-03-02 11:21 ` Patrick McHardy
2009-03-02 22:11 ` Ben Greear
2009-03-02 22:20 ` Patrick McHardy
2009-03-02 22:47 ` David Miller
2009-03-02 23:03 ` Patrick McHardy
2009-03-03 8:48 ` David Miller
2009-03-08 3:36 ` Eric W. Biederman
2009-02-26 16:55 ` Stephen Hemminger
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