[patch 01/18] Driver Core: fis bus rescan devices race

[Greg KH]

From: Daniel Ritz <daniel.ritz@xxxxxx>

bus_rescan_devices_helper() does not hold the dev->sem when it checks for
!dev->driver().  device_attach() holds the sem, but calls again
device_bind_driver() even when dev->driver is set.

What happens is that a first device_attach() call (module insertion time)
is on the way binding the device to a driver.  Another thread calls
bus_rescan_devices().  Now when bus_rescan_devices_helper() checks for
dev->driver it is still NULL 'cos the the prior device_attach() is not yet
finished.  But as soon as the first one releases the dev->sem the second
device_attach() tries to rebind the already bound device again. 
device_bind_driver() does this blindly which leads to a corrupt
driver->klist_devices list (the device links itself, the head points to the
device).  Later a call to device_release_driver() sets dev->driver to NULL
and breaks the link it has to itself on knode_driver.  Rmmoding the driver
later calls driver_detach() which leads to an endless loop 'cos the list
head in klist_devices still points to the device.  And since dev->driver is
NULL it's stuck with the same device forever.  Boom.  And rmmod hangs.

Very easy to reproduce with new-style pcmcia and a 16bit card.  Just loop
modprobe <pcmcia-modules> ;cardctl eject; rmmod <card driver, pcmcia
modules>.

Easiest fix is to check if the device is already bound to a driver in
device_bind_driver().  This avoids the double binding.

Signed-off-by: Daniel Ritz <daniel.ritz@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>


---
drivers/base/dd.c |    3 +++
 1 file changed, 3 insertions(+)

--- scsi-2.6.orig/drivers/base/dd.c	2005-09-20 05:59:41.000000000 -0700
+++ scsi-2.6/drivers/base/dd.c	2005-09-21 17:29:03.000000000 -0700
@@ -40,6 +40,9 @@
  */
 void device_bind_driver(struct device * dev)
 {
+	if (klist_node_attached(&dev->knode_driver))
+		return;
+
 	pr_debug("bound device '%s' to driver '%s'\n",
 		 dev->bus_id, dev->driver->name);
 	klist_add_tail(&dev->knode_driver, &dev->driver->klist_devices);

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