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From: "Jan Klötzke" <jan@kloetzke.net>
To: David Miller <davem@davemloft.net>
Cc: Jan.Kloetzke@preh.de, oneukum@suse.com, netdev@vger.kernel.org,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH] usbnet: fix kernel crash after disconnect
Date: Fri, 19 Apr 2019 09:17:52 +0200	[thread overview]
Message-ID: <20190419071752.GG1084@tuxedo> (raw)
In-Reply-To: <20190418.163544.2153438649838575906.davem@davemloft.net>

Hi David,

On Thu, Apr 18, 2019 at 04:35:44PM -0700, David Miller wrote:
> From: Kloetzke Jan <Jan.Kloetzke@preh.de>
> Date: Thu, 18 Apr 2019 08:02:59 +0000
> 
> > I think this assumption is not correct. As far as I understand the
> > networking code it is still possible that the ndo_start_xmit callback
> > is called while ndo_stop is running and even after ndo_stop has
> > returned. You can only be sure after unregister_netdev() has returned.
> > Maybe some networking folks can comment on that.
> 
> The kernel loops over the devices being unregistered, and first it clears
> the __LINK_STATE_START on all of them, then it invokes ->ndo_stop() on
> all of them.
> 
> __LINK_STATE_START controls what netif_running() returns.
> 
> All calls to ->ndo_start_xmit() are guarded by netif_running() checks.
> 
> So when ndo_stop is invoked you should get no more ndo_start_xmit
> invocations on that device.  Otherwise how could you shut down DMA
> resources and turn off the TX engine properly?

But you could still race with another CPU that is past the
netif_running() check, can you? So the driver has to make sure that it
gracefully handles concurrent ->ndo_start_xmit() and ->ndo_stop() calls.

Or are there any locks/barriers involved that make sure all
->ndo_start_xmit() calls have returned before invoking ->ndo_stop()?

Regards,
Jan

  reply	other threads:[~2019-04-19 20:13 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-17  9:19 [PATCH] usbnet: fix kernel crash after disconnect Kloetzke Jan
2019-04-18  6:37 ` Oliver Neukum
2019-04-18  8:02   ` Kloetzke Jan
2019-04-18 23:35     ` David Miller
2019-04-19  7:17       ` Jan Klötzke [this message]
2019-04-29 18:48         ` Oliver Neukum
2019-04-30 14:08           ` Kloetzke Jan
2019-04-30 14:15           ` [PATCH v2] " Kloetzke Jan
2019-05-05  7:45             ` David Miller
2019-05-06  8:17               ` Oliver Neukum
2019-05-16  7:10                 ` Kloetzke Jan
2019-05-21  0:09                   ` David Miller
2019-05-21  9:48                   ` Oliver Neukum
2019-05-21 10:12                     ` Kloetzke Jan
2019-05-21 11:42                       ` Oliver Neukum
2019-05-21 13:18                         ` [PATCH v3] " Kloetzke Jan
2019-05-21 20:47                           ` David Miller

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