From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
To: "Bjørn Mork" <bjorn@mork.no>
Cc: Oliver Neukum <oneukum@suse.de>,
David Miller <davem@davemloft.net>,
netdev@vger.kernel.org, linux-usb@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] usbnet: Fix a race between usbnet_stop() and the BH
Date: Mon, 31 Aug 2015 11:50:31 +0300 [thread overview]
Message-ID: <55E41557.1060803@rosalab.ru> (raw)
In-Reply-To: <87io7vzzdl.fsf@nemi.mork.no>
31.08.2015 10:32, Bjørn Mork пишет:
> Eugene Shatokhin <eugene.shatokhin@rosalab.ru> writes:
>> 28.08.2015 11:55, Bjørn Mork пишет:
>>
>>> I guess you are right. At least I cannot prove that you are not :)
>>>
>>> There is a bit too much complexity involved here for me...
>>
>> :-)
>>
>> Yes, it is quite complex.
>>
>> I admit, it was easier for me to find the races in usbnet (the tools
>> like KernelStrider and RaceHound do the dirty work) than to analyze
>> their consequences. The latter often requires some time and effort,
>> and so it did this time.
>>
>> Well, any objections to this patch?
>
> No objections from me.
>
> But I would have liked it much better if the code became simpler instead
> of more complex.
Me too, but I can see no other way here. The code is simpler without
locking, indeed, but locking is needed to prevent the problems described
earlier.
One needs to make sure that checking if txq or rxq is empty in
usbnet_terminate_urbs() cannot get inbetween of processing of these
queues and dev->done in defer_bh(). So 'list' and 'dev->done' must be
updated under a common lock in defer_bh(). list->lock is an obvious
candidate for this.
For the same reason, skb_queue_empty(q) must be called under q->lock. So
the code takes it, calls skb_queue_empty(q) and then releases it to wait
a little. Rinse and repeat.
The last complex piece is that spin_lock_nested() in defer_bh. It is
safe to take both list->lock and dev->done.lock there (defer_bh can only
be called for list = dev->rxq or dev->txq but not for dev->done). For
lockdep, however, this is suspicious because '*list' and 'dev->done' are
of the same type so the lock class is the same. So it complained.
To tell lockdep it is OK to use such locking scheme in this particular
case, the recommended pattern was used: spin_lock_nested with
SINGLE_DEPTH_NESTING.
Regards,
Eugene
next prev parent reply other threads:[~2015-08-31 8:50 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-20 18:13 Several races in "usbnet" module (kernel 4.1.x) Eugene Shatokhin
2015-07-21 12:04 ` Oliver Neukum
2015-07-24 17:38 ` Eugene Shatokhin
2015-07-27 12:29 ` Oliver Neukum
2015-07-27 13:53 ` Eugene Shatokhin
2015-07-21 13:07 ` Oliver Neukum
2015-07-21 14:22 ` Oliver Neukum
2015-07-22 18:33 ` Eugene Shatokhin
2015-07-23 9:15 ` Oliver Neukum
2015-07-24 14:41 ` Eugene Shatokhin
2015-07-27 10:00 ` Oliver Neukum
2015-07-27 14:23 ` Eugene Shatokhin
2015-08-14 16:55 ` Eugene Shatokhin
2015-08-14 16:58 ` [PATCH] usbnet: Fix two races between usbnet_stop() and the BH Eugene Shatokhin
2015-08-19 1:54 ` David Miller
2015-08-19 7:57 ` Eugene Shatokhin
2015-08-19 10:54 ` Bjørn Mork
2015-08-19 11:59 ` Eugene Shatokhin
2015-08-19 12:31 ` Bjørn Mork
2015-08-24 12:20 ` Eugene Shatokhin
2015-08-24 13:29 ` Bjørn Mork
2015-08-24 17:00 ` Eugene Shatokhin
2015-08-25 12:31 ` Oliver Neukum
2015-08-24 17:43 ` David Miller
2015-08-24 18:06 ` Alan Stern
2015-08-24 18:21 ` Alan Stern
2015-08-25 12:36 ` Oliver Neukum
2015-08-24 18:35 ` David Miller
2015-08-24 18:12 ` Eugene Shatokhin
2015-07-23 9:43 ` Several races in "usbnet" module (kernel 4.1.x) Oliver Neukum
2015-07-23 11:39 ` Eugene Shatokhin
2015-08-24 20:13 ` [PATCH 0/2] usbnet: Fix 2 problems in usbnet_stop() Eugene Shatokhin
2015-08-24 20:13 ` [PATCH 1/2] usbnet: Get EVENT_NO_RUNTIME_PM bit before it is cleared Eugene Shatokhin
2015-08-25 13:01 ` Oliver Neukum
2015-08-25 14:16 ` Bjørn Mork
2015-08-25 14:22 ` Oliver Neukum
2015-08-26 2:44 ` David Miller
2015-08-24 20:13 ` [PATCH 2/2] usbnet: Fix a race between usbnet_stop() and the BH Eugene Shatokhin
2015-08-24 21:01 ` Bjørn Mork
2015-08-28 8:09 ` Eugene Shatokhin
2015-08-28 8:55 ` Bjørn Mork
2015-08-28 10:42 ` Eugene Shatokhin
2015-08-31 7:32 ` Bjørn Mork
2015-08-31 8:50 ` Eugene Shatokhin [this message]
2015-09-01 7:58 ` Oliver Neukum
2015-09-01 13:54 ` Eugene Shatokhin
2015-09-01 14:05 ` [PATCH] " Eugene Shatokhin
2015-09-08 7:24 ` Eugene Shatokhin
2015-09-08 7:37 ` Bjørn Mork
2015-09-08 7:48 ` Oliver Neukum
2015-09-08 20:18 ` David Miller
2015-09-01 7:57 ` [PATCH 2/2] " Oliver Neukum
2015-08-26 2:45 ` David Miller
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