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[23.128.96.18]) by mx.google.com with ESMTP id i8si30044843pgv.406.2021.10.07.05.42.34; Thu, 07 Oct 2021 05:42:48 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@geanix.com header.s=first header.b=ZtSPiNml; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=geanix.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241343AbhJGMlP (ORCPT + 99 others); Thu, 7 Oct 2021 08:41:15 -0400 Received: from first.geanix.com ([116.203.34.67]:37344 "EHLO first.geanix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233145AbhJGMlN (ORCPT ); Thu, 7 Oct 2021 08:41:13 -0400 Received: from skn-laptop (unknown [185.17.218.86]) by first.geanix.com (Postfix) with ESMTPSA id 6747FC38AD; Thu, 7 Oct 2021 12:39:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=geanix.com; s=first; t=1633610357; bh=gap7Kd40aiSOak1xNMAurxLqrfVo/s5iZGzZdq6IBm8=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ZtSPiNmlrjmHUMzlTsujBrrcz+58ly2fhLzSb/Vf82OTurAWrbWVfvXDJ3ID7TvCD 1RWTYm0nUTAgXjThvBXSQ/zqdiYy3VtX10k5F15hfrB5GWEFSzW3G5BjPhooxPWm1k JIfVDMSdcawkbZ94mkauxPkw8ret/TPyRpKs6T4ai1SH8Gksw4XWiYOF6wnTQsaXGv Hau/mUiH5dlWnAEqmC0BsqfXnRTjdzPljXjK+Gp09KEgJJNocjKdoa7Fdf1FbsRd/l iUhj3DhTGkxCrABQEbQ2IOsVSVVugTffuEPB0bO5V1W+TkP8lRJyFW6x1CJ0D6KZ6E B+ezAs1wIDjYg== Date: Thu, 7 Oct 2021 14:39:16 +0200 From: Sean Nyekjaer To: Boris Brezillon 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: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20211007141858.314533f2@collabora.com> X-Spam-Status: No, score=-3.1 required=4.0 tests=ALL_TRUSTED,BAYES_00, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,URIBL_BLOCKED autolearn=disabled version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on 13e2a5895688 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 07, 2021 at 02:18:58PM +0200, Boris Brezillon wrote: > On Thu, 7 Oct 2021 13:43:51 +0200 > Sean Nyekjaer wrote: > [ ... ] > > > > I have a proposal [0] and yes I have ended up in many deadlocks during > > testing. The hardest part is the locking when going into suspend. > > I'm not sure the wait_queue is initialized the right place :) > > And I'm kinda abusing the nand_get_device() for this... > > > > Who do you think we should add to the discussion? > > > > /Sean > > > > [0]: > > diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c > > index 3d6c6e880520..735dfff18143 100644 > > --- a/drivers/mtd/nand/raw/nand_base.c > > +++ b/drivers/mtd/nand/raw/nand_base.c > > As I said previously, I think this should be handled MTD level > (drivers/mtd/mtdcore.c) not in the raw NAND framework. > > > @@ -337,11 +337,10 @@ static int nand_isbad_bbm(struct nand_chip *chip, loff_t ofs) > > */ > > static int nand_get_device(struct nand_chip *chip) > > { > > + struct mtd_info *mtd = nand_to_mtd(chip); > > + > > + wait_event(mtd->wait_queue, atomic_read(&chip->suspended) == 0); > > mutex_lock(&chip->lock); > > - if (chip->suspended) { > > - mutex_unlock(&chip->lock); > > - return -EBUSY; > > - } > > There's a race here: the device might enter suspend again before you're > able to acquire the lock. > Thought so :) > > mutex_lock(&chip->controller->lock); > > > > return 0; > > @@ -4562,11 +4561,15 @@ static int nand_suspend(struct mtd_info *mtd) > > struct nand_chip *chip = mtd_to_nand(mtd); > > int ret = 0; > > > > + atomic_inc(&chip->suspended); > > mutex_lock(&chip->lock); > > And it's racy here as well: you mark the device as suspended before you > even acquired the lock. > > > if (chip->ops.suspend) > > ret = chip->ops.suspend(chip); > > - if (!ret) > > - chip->suspended = 1; > > + if (ret) { > > + /* Wake things up again if suspend fails */ > > + atomic_dec(&chip->suspended); > > + wake_up(&mtd->wait_queue); > > + } > > mutex_unlock(&chip->lock); > > > > return ret; > > @@ -4581,10 +4584,12 @@ static void nand_resume(struct mtd_info *mtd) > > struct nand_chip *chip = mtd_to_nand(mtd); > > > > mutex_lock(&chip->lock); > > - if (chip->suspended) { > > + if (atomic_read(&chip->suspended)) { > > if (chip->ops.resume) > > chip->ops.resume(chip); > > - chip->suspended = 0; > > + > > + atomic_dec(&chip->suspended); > > + wake_up(&mtd->wait_queue); > > } else { > > pr_err("%s called for a chip which is not in suspended state\n", > > __func__); > > @@ -5099,6 +5104,9 @@ static int nand_detect(struct nand_chip *chip, struct nand_flash_dev *type) > > pr_info("%d MiB, %s, erase size: %d KiB, page size: %d, OOB size: %d\n", > > (int)(targetsize >> 20), nand_is_slc(chip) ? "SLC" : "MLC", > > mtd->erasesize >> 10, mtd->writesize, mtd->oobsize); > > + > > + init_waitqueue_head(&mtd->wait_queue); > > + > > It's an MTD field. It should be initialized somewhere in mtdcore.c. > > > 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? If we introduce a new lock, do we really need to have the suspended as an atomic? I will test with some wait and retry added to nand_get_device().