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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67FF3CCA473 for ; Tue, 21 Jun 2022 15:03:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352151AbiFUPDp (ORCPT ); Tue, 21 Jun 2022 11:03:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241043AbiFUPDo (ORCPT ); Tue, 21 Jun 2022 11:03:44 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 787A3EE0C; Tue, 21 Jun 2022 08:03:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 88027B81986; Tue, 21 Jun 2022 15:03:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF796C341C0; Tue, 21 Jun 2022 15:03:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655823818; bh=TeKpBgZ5AtJxmhayOWO6WbaRDT2YEhFN+BeyLDwSZmA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=e+Tq+QQux5tZDaPO9erymJdHZjUs+rYiDDKRz3FYLsASggUPzkJ1Vhx4L09Q7WV2m x1FtPAnOqwdSqwOuQuDFtTTCPS36lyZ/zF9qwaCfmiHyZqai5jbTfummAbHYDRaao7 XC4lBtlHiBy/mAyUtb++9TnNbeaqHqd6khSboR+0= Date: Tue, 21 Jun 2022 17:03:35 +0200 From: Greg Kroah-Hartman To: Vincent MAILHOL Cc: Marc Kleine-Budde , Rhett Aultman , linux-usb@vger.kernel.org, linux-can , Oliver Neukum , Alan Stern Subject: Re: [PATCH v3 1/2] drivers: usb/core/urb: Add URB_FREE_COHERENT Message-ID: References: <20220610213335.3077375-1-rhett.aultman@samsara.com> <20220610213335.3077375-2-rhett.aultman@samsara.com> <20220611153104.sksoxn4dmo5rgnk3@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Tue, Jun 21, 2022 at 11:59:16PM +0900, Vincent MAILHOL wrote: > On Tue. 21 Jun 2022 at 22:56, Greg Kroah-Hartman > wrote: > > On Sun, Jun 12, 2022 at 01:06:37AM +0900, Vincent MAILHOL wrote: > > > On Sun. 12 juin 2022 at 00:31, Marc Kleine-Budde wrote: > > > > On 10.06.2022 17:33:35, Rhett Aultman wrote: > > > > > From: Vincent Mailhol > > > > > > > > > > When allocating URB memory with kmalloc(), drivers can simply set the > > > > > URB_FREE_BUFFER flag in urb::transfer_flags and that way, the memory > > > > > will be freed in the background when killing the URB (for example with > > > > > usb_kill_anchored_urbs()). > > > > > > > > > > However, there are no equivalent mechanism when allocating DMA memory > > > > > (with usb_alloc_coherent()). > > > > > > > > > > This patch adds a new flag: URB_FREE_COHERENT. Setting this flag will > > > > > cause the kernel to automatically call usb_free_coherent() on the > > > > > transfer buffer when the URB is killed, similarly to how > > > > > URB_FREE_BUFFER triggers a call to kfree(). > > > > > > > > > > In order to have all the flags in numerical order, URB_DIR_IN is > > > > > renumbered from 0x0200 to 0x0400 so that URB_FREE_COHERENT can reuse > > > > > value 0x0200. > > > > > > > > > > Co-developed-by: Vincent Mailhol > > > > > Signed-off-by: Vincent Mailhol > > > > > Co-developed-by: Rhett Aultman > > > > > Signed-off-by: Rhett Aultman > > > > > Reviewed-by: Vincent Mailhol > > > > > > > > FWIW: > > > > Acked-by: Marc Kleine-Budde > > > > > > > > This patch probably goes upstream via USB. Once this is in net I'll take > > > > the 2nd patch. > > > > > > Question to Greg: can this first patch also be applied to the stable > > > branches? Technically, this is a new feature but it will be used to > > > solve several memory leaks on existing drivers (the gs_usb is only one > > > example). > > > > We take in dependent patches into the stable trees all the time when > > needed, that's not an issue here. > > > > What is an issue here is that this feels odd as other USB developers > > said previously. > > > > My big objection here is what validates that the size of the transfer > > buffer here is really the size of the buffer to be freed? Is that > > always set properly to be the length that was allocated? That might > > just be the size of the last transfer using this buffer, but there is no > > guarantee that I can see of that says this really is the length of the > > allocated buffer, which is why usb_free_coherent() requires a size > > parameter. > > Thanks for the comment. > > I (probably wrongly) assumed that urb::transfer_buffer_length was the > allocated length and urb::actual_length was what was actually being > transferred. Right now, I am just confused. Seems that I need to study > a bit more and understand the real purpose of > urb::transfer_buffer_length because I still fail to understand in > which situation this can be different from the allocated length. > > > If that guarantee is always right, then we should be able to drop the > > size option in usb_free_coherent(), and I don't think that's really > > possible. > > I do not follow you on this comment. usb_free_coherent() does not have > a reference to the URB, right? How would it be supposed to retrieve > urb::transfer_buffer_length? Ah, good point. Along those lines, how do you know what the `dma` parameter should be set to as well? thanks, greg k-h