From: "Bjørn Mork" <bjorn@mork.no>
To: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
Cc: David Miller <davem@davemloft.net>,
oneukum@suse.com, netdev@vger.kernel.org,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usbnet: Fix two races between usbnet_stop() and the BH
Date: Wed, 19 Aug 2015 14:31:12 +0200 [thread overview]
Message-ID: <877fore9yn.fsf@nemi.mork.no> (raw)
In-Reply-To: <55D46F85.50608@rosalab.ru> (Eugene Shatokhin's message of "Wed, 19 Aug 2015 14:59:01 +0300")
Eugene Shatokhin <eugene.shatokhin@rosalab.ru> writes:
> The problem is not in the reordering but rather in the fact that
> "dev->flags = 0" is not necessarily atomic
> w.r.t. "clear_bit(EVENT_RX_KILL, &dev->flags)", and vice versa.
>
> So the following might be possible, although unlikely:
>
> CPU0 CPU1
> clear_bit: read dev->flags
> clear_bit: clear EVENT_RX_KILL in the read value
>
> dev->flags=0;
>
> clear_bit: write updated dev->flags
>
> As a result, dev->flags may become non-zero again.
Ah, right. Thanks for explaining.
> I cannot prove yet that this is an impossible situation. If anyone
> can, please explain. If so, this part of the patch will not be needed.
I wonder if we could simply move the dev->flags = 0 down a few lines to
fix both issues? It doesn't seem to do anything useful except for
resetting the flags to a sane initial state after the device is down.
Stopping the tasklet rescheduling etc depends only on netif_running(),
which will be false when usbnet_stop is called. There is no need to
touch dev->flags for this to happen.
>> The EVENT_NO_RUNTIME_PM bug should definitely be fixed. Please split
>> that out as a separate fix. It's a separate issue, and should be
>> backported to all maintained stable releases it applies to (anything
>> from v3.8 and newer)
>
> Yes, that makes sense. However, this fix was originally provided by
> Oliver Neukum rather than me, so I would like to hear his opinion as
> well first.
If what I write above is correct (please help me verify...), then maybe
it does make sense to do these together anyway.
Bjørn
next prev parent reply other threads:[~2015-08-19 12:31 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
[not found] ` <1437480243.3823.5.camel-IBi9RG/b67k@public.gmane.org>
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
[not found] ` <55AD3A41.2040100-irhHPgl+04UvJsYlp49lxw@public.gmane.org>
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
[not found] ` <20150818.185407.1667358232705414236.davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
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 [this message]
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
[not found] ` <20150824.104328.554582952440857559.davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
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
[not found] ` <1440507709.13824.6.camel-IBi9RG/b67k@public.gmane.org>
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
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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