On Mon, Jan 09, 2012 at 11:37:57AM -0500, Alan Stern wrote: > On Mon, 9 Jan 2012, Dmitry Torokhov wrote: > > > > I don't think any of those calls actually accomplish anything, but it's > > > hard to be certain. Some of them appear to be futile attempts to > > > prevent the driver from being unregistered or unloaded, others are > > > there simply to drop the reference taken by driver_find(). > > > > > > In a few of them it's obvious that the driver can't be unregistered > > > while the critical section runs, but in the others I can't tell. On > > > the other hand, if a critical section can race with unregistration > > > then the code is buggy now. > > > > > > What do you think? > > > > I think we need to audit them and decide on case-by-case basis. For > > example drivers/s390/cio/device.c is completely nonsensical: it takes a > > reference on a driver that is passed as argument before calling > > driver_find_device(). But if passed driver was valid before we called > > get_driver it won't become any more valid afterwards and it should not > > disappear either. > > > > drivers/s390/cio/ccwgroup.c - calls are useless; > > > > Authors of drivers/net/phy/phy_device.c had their reservations: > > > > /* Make sure the driver is held. > > * XXX -- Is this correct? */ > > drv = get_driver(phydev->dev.driver); > > > > However it is in phydev_probe() and I hope our device core takes care of > > not destroying drivers in the middle of binding to a device. > > Yes, it does. That one looks like a misunderstanding. It calls > get_driver during phy_probe and put_driver during phy_remove, which > accomplishes nothing. > > > drivers/ssb/main.c seems like needs some protection but does it > > incorrectly as we do not wait for drivers to drop all references before > > unloading modules. > > Possibly it needs to be replaced with try_module_get. I'll send out an > email to the maintainers of these drivers to see what they think. No, I am not that try_module_get() [alone] is quite what is needed, as strictly speaking driver lifetime does not need to be the same as module lifetime. But maybe I am just splitting hair as all drivers are statically initialized and are tied to their modules... -- Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
