From: David Miller <davem@davemloft.net>
To: eugene.shatokhin@rosalab.ru
Cc: 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: Tue, 18 Aug 2015 18:54:07 -0700 (PDT) [thread overview]
Message-ID: <20150818.185407.1667358232705414236.davem@davemloft.net> (raw)
In-Reply-To: <1439571516-11862-1-git-send-email-eugene.shatokhin@rosalab.ru>
From: Eugene Shatokhin <eugene.shatokhin@rosalab.ru>
Date: Fri, 14 Aug 2015 19:58:36 +0300
> 2. The second race is on dev->flags.
>
> dev->flags is set to 0 here:
> *0 usbnet_stop (usbnet.c:816)
> /* deferred work (task, timer, softirq) must also stop.
> * can't flush_scheduled_work() until we drop rtnl (later),
> * else workers could deadlock; so make workers a NOP.
> */
> dev->flags = 0;
> del_timer_sync (&dev->delay);
> tasklet_kill (&dev->bh);
>
> And here, the code clears EVENT_RX_KILL bit in dev->flags, which may
> execute concurrently with the above operation:
> *0 clear_bit (bitops.h:113, inlined)
> *1 usbnet_bh (usbnet.c:1475)
> /* restart RX again after disabling due to high error rate */
> clear_bit(EVENT_RX_KILL, &dev->flags);
>
> It seems, setting dev->flags to 0 is not necessarily atomic w.r.t.
> clear_bit() and other bit operations with dev->flags. It is safer to
> make it atomic and this way, make the race harmless.
>
> While at it, the checking of EVENT_NO_RUNTIME_PM bit of dev->flags in
> usbnet_stop() was fixed too: the bit should be checked before dev->flags
> is cleared.
The fix for this is excessive.
Instead of all of this madness, looping over expensive clear_bit()
atomics, just do whatever it takes to make sure that usbnet_bh() is
quiesced and cannot execute any more. Then you can safely clear
dev->flags normally.
next prev parent reply other threads:[~2015-08-19 1:54 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 [this message]
[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
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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