linux-kernel - Re: [PATCH] driver core: fix possible missing of device probe

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Message-ID: <20120928084652.GC7916@n2100.arm.linux.org.uk>
Date:	Fri, 28 Sep 2012 09:46:52 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] driver core: fix possible missing of device probe

On Fri, Sep 28, 2012 at 08:52:43AM +0800, Ming Lei wrote:
> Inside bus_add_driver(), one device might be added into
> the bus or probed which is triggered by deferred probe
> just after completing of driver_attach() and before
> 'klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers)',
> so the device won't be probed by this driver.
> 
> This patch moves the below line
> 
> 	'klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers)'
> 
> before driver_attach() inside bus_add_driver().
> 
> So fixes the problem since the below way can guarantee that
> no probe(dev) may be lost.
> 
> CPU0                            	CPU1
> driver_register
> 	...
> 	write(bus->driver_list)
> 	smp_mb()
> 	read(bus->device_list)
> 	...
> 					device_add
> 						/* bus_add_device */
> 						write(bus->device_list)
> 						smp_mb()
> 						/* bus_probe_device*/
> 						read(bus->driver_list)
> 
> And the smp_mb() has been implicit by UNLOCK+LOCK
> of 'klist' according to 'VARIETIES OF MEMORY BARRIER' part
> of Documentation/memory-barriers.txt.
> 
> Reported-and-Tested-by: Russell King <linux@....linux.org.uk>

Please use rmk+kernel@....linux.org.uk here, thanks.
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