Hi Arnd, On 10/22/2015 12:29 PM, Arnd Bergmann wrote: > On Thursday 22 October 2015 11:42:02 Eric Auger wrote: >> Currently reset lookup is done on probe. This introduces a >> race with new registration mechanism in the case where the >> vfio-platform driver is bound to the device before its module >> is loaded: on the load, the probe happens which triggers the >> reset module load which itself attempts to get the symbol for >> the registration function (vfio_platform_register_reset). The >> symbol is not yet available hence the lookup fails. In case we >> do the lookup in the first open we are sure the vfio-platform >> module is loaded and vfio_platform_register_reset is available. >> >> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx> > > I don't understand the explanation. I would expect the request_module() > call to block until the module is actually loaded. Is this not > what happens? Again many thanks for this new review. My understanding is the following 1) vfio-platform is attached to the device through the override mechanism 2) vfio-platform get loaded through modprobe: 2-1) the platform driver init function eventually calls the vfio-platform probe function. 2-2) request_module of vfio-platform-calxedaxgmac gets called. 3) The init of vfio-platform-calxedaxgmac looks for vfio_platform_register_reset. Unfortunately at that stage the init of vfio-platform is not completed so the symbol is not available 3-1) in case symbol_get is used in vfio_platform_calxedaxgmac init, as of today, this latter simply returns -EINVAL. Reset registration failed but no stall. 3-2) in case symbol_get is *not* used, I think the module loader attempts to load vfio-platform, which is already under load and this causes a stall. Let me know if you think this understanding is not correct. Best Regards Eric > >> mutex_unlock(&driver_lock); >> @@ -181,6 +182,8 @@ static int vfio_platform_open(void *device_data) >> if (ret) >> goto err_irq; >> >> + vfio_platform_get_reset(vdev); >> + >> if (vdev->reset) >> vdev->reset(vdev); >> > > This needs some error handling to ensure that the open() fails > if there is no reset handler. > > Arnd > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
