From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C918AC04E87 for ; Tue, 21 May 2019 13:24:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 988E92173C for ; Tue, 21 May 2019 13:24:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728294AbfEUNYc (ORCPT ); Tue, 21 May 2019 09:24:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:39896 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727044AbfEUNYb (ORCPT ); Tue, 21 May 2019 09:24:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3EA72ADCB; Tue, 21 May 2019 13:24:30 +0000 (UTC) Message-ID: <1558444291.12672.23.camel@suse.com> Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation From: Oliver Neukum To: Alan Stern , Christoph Hellwig Cc: Jaewon Kim , linux-mm@kvack.org, gregkh@linuxfoundation.org, Jaewon Kim , m.szyprowski@samsung.com, ytk.lee@samsung.com, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Tue, 21 May 2019 15:11:31 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mo, 2019-05-20 at 10:16 -0400, Alan Stern wrote: > On Mon, 20 May 2019, Christoph Hellwig wrote: > > > GFP_KERNEL if you can block, GFP_ATOMIC if you can't for a good reason, > > that is the allocation is from irq context or under a spinlock. If you > > think you have a case where you think you don't want to block, but it > > is not because of the above reasons we need to have a chat about the > > details. > > What if the allocation requires the kernel to swap some old pages out > to the backing store, but the backing store is on the device that the > driver is managing? The swap can't take place until the current I/O > operation is complete (assuming the driver can handle only one I/O > operation at a time), and the current operation can't complete until > the old pages are swapped out. Result: deadlock. > > Isn't that the whole reason for using GFP_NOIO in the first place? Hi, lookig at this it seems to me that we are in danger of a deadlock - during reset - devices cannot do IO while being reset covered by the USB layer in usb_reset_device - resume & restore - devices cannot do IO while suspended covered by driver core in rpm_callback - disconnect - a disconnected device cannot do IO is this a theoretical case or should I do something to the driver core? How about changing configurations on USB? Regards Oliver