From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
To: David Miller <davem@davemloft.net>
Cc: bjorn@mork.no, 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: Mon, 24 Aug 2015 21:12:26 +0300 [thread overview]
Message-ID: <55DB5E8A.9040108@rosalab.ru> (raw)
In-Reply-To: <20150824.104328.554582952440857559.davem@davemloft.net>
24.08.2015 20:43, David Miller пишет:
> From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
> Date: Wed, 19 Aug 2015 14:59:01 +0300
>
>> 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.
>
> Is this really possible?
On x86, it is not possible, so this is not a problem. Perhaps, for ARM
too. As for the other architectures supported by the kernel - not sure,
no common guarantees, it seems. Anyway, this is not a critical issue, I
agree.
OK, let us leave things as they are for this one and fix the rest.
>
> Stores really are "atomic" in the sense that the do their update
> in one indivisible operation.
>
> Atomic operations like clear_bit also will behave that way.
>
> If a clear_bit is in progress, the "dev->flags=0" store will not be
> able to grab the cache line exclusively until the clear_bit is done.
>
> So I think the above sequent of events is completely impossible. Once
> a clear_bit starts, a write by another foreign agent on the bus is
> absolutely impossible to legally occur until the clear_bit completes.
>
> I think this is a non-issue.
>
Regards,
Eugene
next prev parent reply other threads:[~2015-08-24 18:12 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
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 [this message]
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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