On Wed, Oct 10, 2012 at 6:08 PM, Oliver Neukum <oneukum@xxxxxxx> wrote: > > A reset always applies to the whole device. Resets are used in error > handling of block devices (storage and uas). If you reset a device, > pre_reset() and post_reset() of all interfaces need to be called. So they > are part of the SCSI error handler. SCSI error handlers can allocate memory > only with GFP_NOIO (or GFP_ATOMIC) because any IO for paging > can cause the SCSI layer to wait for the error handling to finish. The error > handling can only finish when pre/post_reset() have finished. Catch-22 IMO, it is not practical to obey the rule for drivers, because driver may call many other kernel component API which may allocate memory via GFP_KERNEL in the path easily. Same with runtime PM case. > > So any control messages in block error handling need to use GFP_NOIO. > If you look at the control message helpers in usbcore you will find a lot > of GFP_NOIO. That is the reason. If one driver has no .pre_reset or .post_reset, usb_reset_device() will try to unbind&bind the interface, so you mean these usb drivers have to use GFP_NOIO to allocate memory in its probe() and disconnect()? Unfortunately, that is not true, and no way to make sure all memory allocations in the path via GFP_NOIO, IMO. Also, only very few drivers have implemented .pre_reset and .post_reset. Thanks, -- Ming Lei -- 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
