Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753756Ab3CKQIs (ORCPT ); Mon, 11 Mar 2013 12:08:48 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:50257 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751526Ab3CKQIr (ORCPT ); Mon, 11 Mar 2013 12:08:47 -0400 Date: Mon, 11 Mar 2013 12:08:46 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Ming Lei cc: Alexey Khoroshilov , Greg Kroah-Hartman , Hans de Goede , , , Subject: Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1308 Lines: 34 On Mon, 11 Mar 2013, Ming Lei wrote: > On Mon, Mar 11, 2013 at 11:32 PM, Alan Stern 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-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/