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 248E7C433F5 for ; Mon, 4 Oct 2021 08:42:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF70B6101B for ; Mon, 4 Oct 2021 08:41:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230479AbhJDInq (ORCPT ); Mon, 4 Oct 2021 04:43:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229836AbhJDInm (ORCPT ); Mon, 4 Oct 2021 04:43:42 -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 49BE6C061745 for ; Mon, 4 Oct 2021 01:41:54 -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 2C20F1F422CA; Mon, 4 Oct 2021 09:41:52 +0100 (BST) Date: Mon, 4 Oct 2021 10:41:47 +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: <20211004104147.579f3b01@collabora.com> In-Reply-To: <20211004065608.3190348-1-sean@geanix.com> References: <20211004065608.3190348-1-sean@geanix.com> 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 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(). > > Tested on a iMX6ULL. > > [0]: > ef347c0cfd61 ("mtd: rawnand: gpmi: Implement exec_op") > > Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking") > Signed-off-by: Sean Nyekjaer > --- > > I did this a RFC as we probably will need to remove the suspended > variable as it's kinda made obsolute by this change. > Should we introduce a new mutex? Or maybe a spin_lock? > > drivers/mtd/nand/raw/nand_base.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 3d6c6e880520..0ea343404cac 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c > @@ -4567,7 +4567,6 @@ static int nand_suspend(struct mtd_info *mtd) > ret = chip->ops.suspend(chip); > if (!ret) > chip->suspended = 1; > - mutex_unlock(&chip->lock); Hm, I'm not sure keeping the lock when you're in a suspended state is a good idea. It just papers over another bug IMO (see above). > > return ret; > } > @@ -4580,7 +4579,6 @@ static void nand_resume(struct mtd_info *mtd) > { > struct nand_chip *chip = mtd_to_nand(mtd); > > - mutex_lock(&chip->lock); > if (chip->suspended) { > if (chip->ops.resume) > chip->ops.resume(chip); 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 912BCC433F5 for ; Mon, 4 Oct 2021 08:42:47 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3EB9F6113D for ; Mon, 4 Oct 2021 08:42:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 3EB9F6113D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=collabora.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=xk9bYm0q1I+JwIgSLekuN690CFiOFxOab+xYqlVkckQ=; b=Y9eMh+0g/LArr1 dt5pKLNCWBZe645OCGdfh6ssfM/jGuNQPh5GztMnFaqgGHXAFDsIWJHQm5xE97EIGTCoIqB+Ss082 Ky29ebDtrr60xKwty09OaPyumgqvHeIU7IQ/7HGUy9wOh4MaYI8Y8+rVm4l+c7G2UOkz91ZTuOnfB 8MFBoW1cmxBiEhHd6v4CGqsfwZwmoi5sBXmSgVFVtUEwWk626JA1x2tjswYtf5Xdbs7pCgROvYRiZ 8iCjTJqRZCDMLRM6Nwq1q69QGZg7ySStnI84YLjbdM5ExSa2XjsrMiUXUPCeK6vnsEoC+2ZeXpgY1 zzIT3woPba+vfu04NA9A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mXJXr-005eAn-4o; Mon, 04 Oct 2021 08:41:59 +0000 Received: from bhuna.collabora.co.uk ([2a00:1098:0:82:1000:25:2eeb:e3e3]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mXJXo-005eA6-5H for linux-mtd@lists.infradead.org; Mon, 04 Oct 2021 08:41:57 +0000 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 2C20F1F422CA; Mon, 4 Oct 2021 09:41:52 +0100 (BST) Date: Mon, 4 Oct 2021 10:41:47 +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: <20211004104147.579f3b01@collabora.com> In-Reply-To: <20211004065608.3190348-1-sean@geanix.com> References: <20211004065608.3190348-1-sean@geanix.com> Organization: Collabora X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211004_014156_391985_E43BC5C4 X-CRM114-Status: GOOD ( 28.79 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org 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(). > > Tested on a iMX6ULL. > > [0]: > ef347c0cfd61 ("mtd: rawnand: gpmi: Implement exec_op") > > Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking") > Signed-off-by: Sean Nyekjaer > --- > > I did this a RFC as we probably will need to remove the suspended > variable as it's kinda made obsolute by this change. > Should we introduce a new mutex? Or maybe a spin_lock? > > drivers/mtd/nand/raw/nand_base.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > index 3d6c6e880520..0ea343404cac 100644 > --- a/drivers/mtd/nand/raw/nand_base.c > +++ b/drivers/mtd/nand/raw/nand_base.c > @@ -4567,7 +4567,6 @@ static int nand_suspend(struct mtd_info *mtd) > ret = chip->ops.suspend(chip); > if (!ret) > chip->suspended = 1; > - mutex_unlock(&chip->lock); Hm, I'm not sure keeping the lock when you're in a suspended state is a good idea. It just papers over another bug IMO (see above). > > return ret; > } > @@ -4580,7 +4579,6 @@ static void nand_resume(struct mtd_info *mtd) > { > struct nand_chip *chip = mtd_to_nand(mtd); > > - mutex_lock(&chip->lock); > if (chip->suspended) { > if (chip->ops.resume) > chip->ops.resume(chip); ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/