[PATCH] driver core: fix possible missing of device probe

[Ming Lei]

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@xxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
---
 drivers/base/bus.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 181ed26..3b5bddb 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -714,12 +714,12 @@ int bus_add_driver(struct device_driver *drv)
 	if (error)
 		goto out_unregister;
 
+	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
 	if (drv->bus->p->drivers_autoprobe) {
 		error = driver_attach(drv);
 		if (error)
 			goto out_unregister;
 	}
-	klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
 	module_add_driver(drv->owner, drv);
 
 	error = driver_create_file(drv, &driver_attr_uevent);
-- 
1.7.9.5

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