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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D277EC433EF for ; Mon, 4 Oct 2021 09:58:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA5D1613A8 for ; Mon, 4 Oct 2021 09:58:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232592AbhJDKAP (ORCPT ); Mon, 4 Oct 2021 06:00:15 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:51750 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232577AbhJDKAL (ORCPT ); Mon, 4 Oct 2021 06:00:11 -0400 Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: bbrezillon) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id D5C2E1F42EC7; Mon, 4 Oct 2021 10:58:20 +0100 (BST) Date: Mon, 4 Oct 2021 11:58:17 +0200 From: Boris Brezillon To: Sean Nyekjaer Cc: Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Boris Brezillon , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mtd: rawnand: use mutex to protect access while in suspend Message-ID: <20211004115817.18739936@collabora.com> In-Reply-To: <20211004085509.iikxtdvxpt6bri5c@skn-laptop> References: <20211004065608.3190348-1-sean@geanix.com> <20211004104147.579f3b01@collabora.com> <20211004085509.iikxtdvxpt6bri5c@skn-laptop> Organization: Collabora X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 4 Oct 2021 10:55:09 +0200 Sean Nyekjaer wrote: > On Mon, Oct 04, 2021 at 10:41:47AM +0200, Boris Brezillon wrote: > > On Mon, 4 Oct 2021 08:56:09 +0200 > > Sean Nyekjaer wrote: > > > > > This will prevent nand_get_device() from returning -EBUSY. > > > It will force mtd_write()/mtd_read() to wait for the nand_resume() to unlock > > > access to the mtd device. > > > > > > Then we avoid -EBUSY is returned to ubifsi via mtd_write()/mtd_read(), > > > that will in turn hard error on every error returened. > > > We have seen during ubifs tries to call mtd_write before the mtd device > > > is resumed. > > > > I think the problem is here. Why would UBIFS/UBI try to write something > > to a device that's not resumed yet (or has been suspended already, if > > you hit this in the suspend path). > > > > > > > > Exec_op[0] speed things up, so we see this race when the device is > > > resuming. But it's actually "mtd: rawnand: Simplify the locking" that > > > allows it to return -EBUSY, before that commit it would have waited for > > > the mtd device to resume. > > > > Uh, wait. If nand_resume() was called before any writes/reads this > > wouldn't happen. IMHO, the problem is not that we return -EBUSY without > > blocking, the problem is that someone issues a write/read before calling > > mtd_resume(). > > > > The commit msg from "mtd: rawnand: Simplify the locking" states this clearly. > > """ > Last important change to mention: we now return -EBUSY when someone > tries to access a device that as been suspended, and propagate this > error to the upper layer. > """ > > IMHO "mtd: rawnand: Simplify the locking" should never had been merged > before the upper layers was fixed to handle -EBUSY. ;) > Which they still not are... That's not really the problem here. Upper layers should never get -EBUSY in the first place if the MTD device was resumed before the UBI device. Looks like we have a missing UBI -> MTD parenting link, which would explain why things don't get resumed in the right order. Can you try with the following diff applied? --- diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c index f399edc82191..1981ce8f3a26 100644 --- a/drivers/mtd/ubi/build.c +++ b/drivers/mtd/ubi/build.c @@ -905,6 +905,7 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, ubi->dev.release = dev_release; ubi->dev.class = &ubi_class; ubi->dev.groups = ubi_dev_groups; + ubi->dev.parent = &mtd->dev; ubi->mtd = mtd; ubi->ubi_num = ubi_num;