From: Pidoux <f6bvp@free•fr>
To: Jarek Poplawski <jarkao2@gmail•com>
Cc: Alexey Dobriyan <adobriyan@gmail•com>,
Ralf Baechle DL5RB <ralf@linux-mips•org>,
Linux Netdev List <netdev@vger•kernel.org>
Subject: Re: [ROSE] [AX25] possible circular locking
Date: Fri, 28 Dec 2007 22:30:23 +0100 [thread overview]
Message-ID: <47756AEF.8040206@free.fr> (raw)
In-Reply-To: <20071218135202.GA2023@ff.dom.local>
Jarek Poplawski wrote :
> On Mon, Dec 17, 2007 at 11:06:04AM +0100, Bernard Pidoux F6BVP wrote:
>
>> Hi,
>>
>>
>> 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:
>>
> ...
>
> It seems, lockdep is warried 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 this other bug nearby 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. But, since I don't know AX25 & ROSE at all, this
> should be necessarily verified by somebody who knows these things.
>
> I attach here my very experimental proposal with breaking the lock
> for ax25_disconnect(), with some failsafe and debugging because of
> this, but, if in this special case the lock is required for some
> other reasons, then this patch should be dumped, of course.
>
> Regards,
> Jarek P.
>
> WARNING:
> not tested, not even compiled, needs some ack before testing!
>
> ---
>
> 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);
>
>
>
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
next prev parent reply other threads:[~2007-12-28 21:30 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-17 10:06 [ROSE] [AX25] possible circular locking Bernard Pidoux F6BVP
2007-12-18 13:52 ` Jarek Poplawski
[not found] ` <476837BF.3070207@free.fr>
2007-12-18 22:04 ` Jarek Poplawski
2007-12-28 21:30 ` Pidoux [this message]
[not found] ` <47755FDB.2070501@free.fr>
2007-12-28 21:48 ` [PATCH][ROSE][AX25] af_ax25: " Jarek Poplawski
2007-12-30 3:14 ` David Miller
2007-12-30 14:13 ` Jarek Poplawski
2007-12-31 5:00 ` David Miller
2008-01-11 5:22 ` David Miller
2008-01-11 9:40 ` Jarek Poplawski
2008-01-12 19:48 ` Bernard Pidoux F6BVP
2008-01-11 21:40 ` [PATCH] [ROSE] two extra tab characters removed Bernard Pidoux F6BVP
2008-02-09 18:44 ` [PATCH][AX25] ax25_ds_timer: use mod_timer instead of add_timer Bernard Pidoux F6BVP
2008-02-09 19:39 ` Jarek Poplawski
2008-02-10 18:07 ` Bernard Pidoux F6BVP
2008-02-09 23:50 ` [PATCH][AX25] af_ax25: remove sock lock in ax25_info_show() Jarek Poplawski
2008-02-10 13:10 ` [PATCH v2][AX25] " Jarek Poplawski
2008-02-12 5:25 ` David Miller
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