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Date: Fri, 28 Dec 2007 22:48:57 +0100
From: Jarek Poplawski <jarkao2@...il.com>
To: David Miller <davem@...emloft.net>
Cc: Pidoux <f6bvp@...e.fr>, Ralf Baechle DL5RB <ralf@...ux-mips.org>,
Alexey Dobriyan <adobriyan@...il.com>,
Linux Netdev List <netdev@...r.kernel.org>
Subject: [PATCH][ROSE][AX25] af_ax25: possible circular locking
On Fri, Dec 28, 2007 at 09:43:07PM +0100, Pidoux wrote:
...
> After a few days of observation and a number of reboot for test purpose, I
> confirm that your patch is doing very well.
> I have no more problems rebooting and the AX25 applications are running
> fine.
>
> I hope this patch, with or without warning, could be applied in next kernel
> release.
>
> Thanks again Jarek.
>
> Regards from Bernard P.
> f6bvp
Thanks again Bernard.
Jarek P. too
---------------->
Subject: [ROSE][AX25] af_ax25: possible circular locking
Bernard Pidoux F6BVP reported:
> When I killall kissattach I can see the following message.
>
> This happens on kernel 2.6.24-rc5 already patched with the 6 previously
> patches I sent recently.
>
>
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.23.9 #1
> -------------------------------------------------------
> kissattach/2906 is trying to acquire lock:
> (linkfail_lock){-+..}, at: [<d8bd4603>] ax25_link_failed+0x11/0x39 [ax25]
>
> but task is already holding lock:
> (ax25_list_lock){-+..}, at: [<d8bd7c7c>] ax25_device_event+0x38/0x84
> [ax25]
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
...
lockdep is worried about the different order here:
#1 (rose_neigh_list_lock){-+..}:
#3 (ax25_list_lock){-+..}:
#0 (linkfail_lock){-+..}:
#1 (rose_neigh_list_lock){-+..}:
#3 (ax25_list_lock){-+..}:
#0 (linkfail_lock){-+..}:
So, ax25_list_lock could be taken before and after linkfail_lock.
I don't know if this three-thread clutch is very probable (or
possible at all), but it seems another bug reported by Bernard
("[...] system impossible to reboot with linux-2.6.24-rc5")
could have similar source - namely ax25_list_lock held by
ax25_kill_by_device() during ax25_disconnect(). It looks like the
only place which calls ax25_disconnect() this way, so I guess, it
isn't necessary.
This patch is breaking the lock for ax25_disconnect(), with some
failsafe and debugging added to detect unforeseen problems.
Reported-and-tested-by: Bernard Pidoux <f6bvp@...e.fr>
Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
---
diff -Nurp linux-2.6.24-rc5-/net/ax25/af_ax25.c linux-2.6.24-rc5+/net/ax25/af_ax25.c
--- linux-2.6.24-rc5-/net/ax25/af_ax25.c 2007-12-17 13:29:19.000000000 +0100
+++ linux-2.6.24-rc5+/net/ax25/af_ax25.c 2007-12-18 13:36:05.000000000 +0100
@@ -87,10 +87,19 @@ static void ax25_kill_by_device(struct n
return;
spin_lock_bh(&ax25_list_lock);
+again:
ax25_for_each(s, node, &ax25_list) {
if (s->ax25_dev == ax25_dev) {
+ struct hlist_node *nn = node->next;
+
s->ax25_dev = NULL;
+ spin_unlock_bh(&ax25_list_lock);
ax25_disconnect(s, ENETUNREACH);
+ spin_lock_bh(&ax25_list_lock);
+ if (nn != node->next) {
+ WARN_ON_ONCE(1);
+ goto again;
+ }
}
}
spin_unlock_bh(&ax25_list_lock);
--
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