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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4819C2D0A3 for ; Fri, 6 Nov 2020 13:55:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BCA120735 for ; Fri, 6 Nov 2020 13:55:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="k16552k0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727317AbgKFNzf (ORCPT ); Fri, 6 Nov 2020 08:55:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727093AbgKFNzf (ORCPT ); Fri, 6 Nov 2020 08:55:35 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 197F1C0613CF for ; Fri, 6 Nov 2020 05:55:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=YLDzNESoEgKE1MzhkwepgEKB6SaZ/weGVd8fm6priQM=; b=k16552k0mzEOJReuMq3lkLtqUE 16j/0qAT1BZvTmRGnYCX6LxOKmE3ehUYDFNdjjXMGAL/F4P17U/sy8OS/mDEscvzxT7Jg8pQnWQ7G 32utRcIveVGJF+Svo7jE2VABBVDc2j+aInfUF6ljO/W5iVc87pXYhyML4nhmv3ktNpptdmQpFMMi+ pm6+FG+Av8pcqekHEScUhLZn6tG238C1JTUAIX3S9NPqOcRjKghJvFoLGRKJB/1RHgb/e9TKl0q06 D0dkLdPX5d/+L3w/LmN/9o+YvrhFBDt0pUZ36+qnYTLXZU02p+IQ8SzSvNPlB81PewLjY8F/YA25f ykzYzEhg==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kb2DE-0004cf-4b; Fri, 06 Nov 2020 13:55:32 +0000 Date: Fri, 6 Nov 2020 13:55:32 +0000 From: Christoph Hellwig To: Damien Le Moal Cc: linux-block@vger.kernel.org, Jens Axboe Subject: Re: [PATCH] null_blk: Fix scheduling in atomic with zoned mode Message-ID: <20201106135532.GA16634@infradead.org> References: <20201106110141.5887-1-damien.lemoal@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201106110141.5887-1-damien.lemoal@wdc.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Nov 06, 2020 at 08:01:41PM +0900, Damien Le Moal wrote: > Commit aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") changed > zone locking to using the potentially sleeping wait_on_bit_io() > function. This is acceptable when memory backing is enabled as the > device queue is in that case marked as blocking, but this triggers a > scheduling while in atomic context with memory backing disabled. > > Fix this by relying solely on the device zone spinlock for zone > information protection without temporarily releasing this lock around > null_process_cmd() execution in null_zone_write(). This is OK to do > since when memory backing is disabled, command processing does not > block and the memory backing lock nullb->lock is unused. This solution > avoids the overhead of having to mark a zoned null_blk device queue as > blocking when memory backing is unused. > > This patch also adds comments to the zone locking code to explain the > unusual locking scheme. > > Reported-by: kernel test robot > Fixes: aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") > Cc: stable@vger.kernel.org > Signed-off-by: Damien Le Moal > --- > drivers/block/null_blk.h | 2 +- > drivers/block/null_blk_zoned.c | 47 ++++++++++++++++++++++------------ > 2 files changed, 32 insertions(+), 17 deletions(-) > > diff --git a/drivers/block/null_blk.h b/drivers/block/null_blk.h > index cfd00ad40355..c24d9b5ad81a 100644 > --- a/drivers/block/null_blk.h > +++ b/drivers/block/null_blk.h > @@ -47,7 +47,7 @@ struct nullb_device { > unsigned int nr_zones_closed; > struct blk_zone *zones; > sector_t zone_size_sects; > - spinlock_t zone_dev_lock; > + spinlock_t zone_lock; > unsigned long *zone_locks; > > unsigned long size; /* device size in MB */ > diff --git a/drivers/block/null_blk_zoned.c b/drivers/block/null_blk_zoned.c > index 8775acbb4f8f..beb34b4f76b0 100644 > --- a/drivers/block/null_blk_zoned.c > +++ b/drivers/block/null_blk_zoned.c > @@ -46,11 +46,20 @@ int null_init_zoned_dev(struct nullb_device *dev, struct request_queue *q) > if (!dev->zones) > return -ENOMEM; > > - spin_lock_init(&dev->zone_dev_lock); > - dev->zone_locks = bitmap_zalloc(dev->nr_zones, GFP_KERNEL); > - if (!dev->zone_locks) { > - kvfree(dev->zones); > - return -ENOMEM; > + /* > + * With memory backing, the zone_lock spinlock needs to be temporarily > + * released to avoid scheduling in atomic context. To guarantee zone > + * information protection, use a bitmap to lock zones with > + * wait_on_bit_lock_io(). Sleeping on the lock is OK as memory backing > + * implies that the queue is marked with BLK_MQ_F_BLOCKING. > + */ > + spin_lock_init(&dev->zone_lock); > + if (dev->memory_backed) { > + dev->zone_locks = bitmap_zalloc(dev->nr_zones, GFP_KERNEL); > + if (!dev->zone_locks) { > + kvfree(dev->zones); > + return -ENOMEM; > + } > } > > if (dev->zone_nr_conv >= dev->nr_zones) { > @@ -137,12 +146,17 @@ void null_free_zoned_dev(struct nullb_device *dev) > > static inline void null_lock_zone(struct nullb_device *dev, unsigned int zno) > { > - wait_on_bit_lock_io(dev->zone_locks, zno, TASK_UNINTERRUPTIBLE); > + if (dev->memory_backed) > + wait_on_bit_lock_io(dev->zone_locks, zno, TASK_UNINTERRUPTIBLE); > + spin_lock_irq(&dev->zone_lock); > } > > static inline void null_unlock_zone(struct nullb_device *dev, unsigned int zno) > { > - clear_and_wake_up_bit(zno, dev->zone_locks); > + spin_unlock_irq(&dev->zone_lock); > + > + if (dev->memory_backed) > + clear_and_wake_up_bit(zno, dev->zone_locks); > } > > int null_report_zones(struct gendisk *disk, sector_t sector, > @@ -322,7 +336,6 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector, > return null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors); > > null_lock_zone(dev, zno); > - spin_lock(&dev->zone_dev_lock); > > switch (zone->cond) { > case BLK_ZONE_COND_FULL: > @@ -375,9 +388,17 @@ static blk_status_t null_zone_write(struct nullb_cmd *cmd, sector_t sector, > if (zone->cond != BLK_ZONE_COND_EXP_OPEN) > zone->cond = BLK_ZONE_COND_IMP_OPEN; > > - spin_unlock(&dev->zone_dev_lock); > + /* > + * Memory backing allocation may sleep: release the zone_lock spinlock > + * to avoid scheduling in atomic context. Zone operation atomicity is > + * still guaranteed through the zone_locks bitmap. > + */ > + if (dev->memory_backed) > + spin_unlock_irq(&dev->zone_lock); > ret = null_process_cmd(cmd, REQ_OP_WRITE, sector, nr_sectors); > - spin_lock(&dev->zone_dev_lock); > + if (dev->memory_backed) > + spin_lock_irq(&dev->zone_lock); Do we actually need to take zone_lock at all for the memory_backed case? Should the !memory_backed just use a per-zone spinlock?