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 8E26CC43217 for ; Tue, 5 Oct 2021 08:58:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A77D61269 for ; Tue, 5 Oct 2021 08:58:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233658AbhJEJAd (ORCPT ); Tue, 5 Oct 2021 05:00:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233633AbhJEJAc (ORCPT ); Tue, 5 Oct 2021 05:00:32 -0400 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e3e3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B00EC061745 for ; Tue, 5 Oct 2021 01:58:41 -0700 (PDT) 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 3410D1F4385F; Tue, 5 Oct 2021 09:58:39 +0100 (BST) Date: Tue, 5 Oct 2021 10:58:36 +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: <20211005105836.6c300f25@collabora.com> In-Reply-To: <20211005084938.jcbw24umhehoiirs@skn-laptop> References: <20211004065608.3190348-1-sean@geanix.com> <20211004104147.579f3b01@collabora.com> <20211004085509.iikxtdvxpt6bri5c@skn-laptop> <20211004115817.18739936@collabora.com> <20211004101246.kagtezizympxupat@skn-laptop> <20211004134700.26327f6f@collabora.com> <20211005070930.epgxb5qzumk4awxq@skn-laptop> <20211005102300.5da6d480@collabora.com> <20211005084938.jcbw24umhehoiirs@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 Tue, 5 Oct 2021 10:49:38 +0200 Sean Nyekjaer wrote: > On Tue, Oct 05, 2021 at 10:23:00AM +0200, Boris Brezillon wrote: > > On Tue, 5 Oct 2021 09:09:30 +0200 > > Sean Nyekjaer wrote: > > [ ... ] > > > > > > > Have you seen the reproducer script? > > > > How would I know about this script or your previous attempt (mentioned > > at the end of this email) given I was not Cc-ed on the previous > > discussion, and nothing mentions it in this RFC... > > > > That's why I shared it here ;) > Initially I thought this was a bug introduced by exec_op. > > > > --- > > > root@iwg26-v1:/data/root# cat /data/crash.sh > > > #!/bin/sh -x > > > > > > echo enabled > /sys/devices/platform/soc/2100000.bus/21f4000.serial/tty/ttymxc4/power/wakeup > > > > > > rm /data/test50M > > > dd if=/dev/urandom of=/tmp/test50M bs=1M count=50 > > > cp /tmp/test50M /data/ & > > > sleep 1 > > > echo mem > /sys/power/state > > > --- > > > > > > As seen in the log above disk is synced before suspend. > > > cp is continuing to copy data to ubifs. > > > And then user space processes are frozen. > > > At this point the kernel thread would have unwritten data. > > > > > > We tried to solve this with: > > > https://lkml.org/lkml/2021/9/1/280 > > > > I see. It's still unclear to me when the write happens. Is it in the > > suspend path (before the system is actually suspended), or in the > > resume path (when the system is being resumed). > > > > Anyway, let's admit writing to a storage device while it's suspended is > > a valid use case and requires the storage layer to put this request on > > old. This wait should not, IMHO, be handled at the NAND level, but at > > the MTD level (using a waitqueue, and an atomic to make > > suspended/resumed transitions safe). And abusing a mutex to implement > > that is certainly not a good idea. > > I did't say this was the right solution ;) I actually asked in the RFC: > "Should we introduce a new mutex? Or maybe a spin_lock?" > > What are you proposing, a waitqueue in mtd_info? That gets checked in > mtd_write()/mtd_read()? Yes, and replacing the suspended state by an atomic, and providing a helper to wait on the device readiness. Helper you will call in every path involving a communication with the HW, not just mtd_read/write() (you're missing erase at least, and I fear there are other hooks that might lead to commands being issued to the device). But before we get there, I think it's important to understand what the kernel expects. IOW, if and when threads can do a request on a suspended device, and when it's acceptable to wait (vs returning -EBUSY), otherwise I fear we'll end up with deadlocks in the suspend/resume path.