On Mon, 11 Mar 2013, Ming Lei wrote: > On Mon, Mar 11, 2013 at 11:32 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > Of course you have to lock the device before changing its driver. What > > would happen if two different threads tried to change a device's driver > > at the same time? > > Yes, claim/release interface need device lock, but the patch doesn't > touch claim/release command handling. Then why did you ask? You wrote: "Looks device lock isn't required for USB transfer of kernel driver." > > usbdev_do_ioctl() needs to acquire the device lock in order to prevent > > races with driver_disconnect() and usbdev_remove(). > > Looks the patch basically converts the allocation inside URB submit path, > and actually I mean why we need to hold device lock in submitting > URB path? Device lock isn't required before submitting URBs > in kernel driver. In general it isn't, no. But usbfs uses the lock to prevent races with driver_disconnect() -- it is invalid to submit URBs after the disconnect routine has returned. Alan Stern -- 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
