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 2F9E8C433EF for ; Thu, 7 Oct 2021 13:14:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 08B49611C3 for ; Thu, 7 Oct 2021 13:14:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240954AbhJGNQ0 (ORCPT ); Thu, 7 Oct 2021 09:16:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232881AbhJGNQZ (ORCPT ); Thu, 7 Oct 2021 09:16:25 -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 6E527C061570 for ; Thu, 7 Oct 2021 06:14:31 -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 468A31F451F3; Thu, 7 Oct 2021 14:14:29 +0100 (BST) Date: Thu, 7 Oct 2021 15:14:26 +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: <20211007151426.54db0764@collabora.com> In-Reply-To: <20211007123916.w4oaooxfbawe6yw3@skn-laptop> References: <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> <20211005105836.6c300f25@collabora.com> <20211007114351.3nafhtpefezxhanc@skn-laptop> <20211007141858.314533f2@collabora.com> <20211007123916.w4oaooxfbawe6yw3@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 Thu, 7 Oct 2021 14:39:16 +0200 Sean Nyekjaer wrote: > > > return 0; > > > > > > free_detect_allocation: > > > @@ -6264,6 +6272,8 @@ static int nand_scan_tail(struct nand_chip *chip) > > > if (chip->options & NAND_SKIP_BBTSCAN) > > > return 0; > > > > > > + atomic_set(&chip->suspended, 0); > > > + > > > /* Build bad block table */ > > > ret = nand_create_bbt(chip); > > > if (ret) > > > diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h > > > index 88227044fc86..f7dcbc336170 100644 > > > --- a/include/linux/mtd/mtd.h > > > +++ b/include/linux/mtd/mtd.h > > > @@ -360,6 +360,8 @@ struct mtd_info { > > > int (*_get_device) (struct mtd_info *mtd); > > > void (*_put_device) (struct mtd_info *mtd); > > > > > > + wait_queue_head_t wait_queue; > > > + > > > > wait_queue doesn't really describe what this waitqueue is used for > > (maybe resume_wq), and the suspended state should be here as well > > (actually, there's one already). > > I'll rename to something meaningful. > > > > Actually, what we need is a way to prevent the device from being > > suspended while accesses are still in progress, and new accesses from > > being queued if a suspend is pending. So, I think you need a readwrite > > lock here: > > > > * take the lock in read mode for all IO accesses, check the > > mtd->suspended value > > - if true, release the lock, and wait (retry on wakeup) > > - if false, just do the IO > > > > * take the lock in write mode when you want to suspend/resume the > > device and update the suspended field. Call wake_up_all() in the > > resume path > > Could we use the chip->lock mutex for this? It's does kinda what you > described above? No you can't. Remember I suggested to move all of that logic to mtdcore.c, which doesn't know about the nand_chip struct. > If we introduce a new lock, do we really need to have the suspended as > an atomic? Nope, I thought we could do without a lock, but we actually need to track active IO requests, not just the suspended state. > > I will test with some wait and retry added to nand_get_device(). Again, I think there's a misunderstanding here: if you move it to the mtd layer, it can't be done in nand_get_device(). But once you've implemented it in mtdcore.c, you should be able to get rid of the nand_chip->suspended field.