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Wed, 25 Nov 2020 11:45:28 -0500 Received: by smtp.corp.redhat.com (Postfix) id 21689AB40E; Wed, 25 Nov 2020 16:45:28 +0000 (UTC) Received: from mimecast-mx02.redhat.com (mimecast03.extmail.prod.ext.rdu2.redhat.com [10.11.55.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1C174AB40A for ; Wed, 25 Nov 2020 16:45:26 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-2.mimecast.com [207.211.31.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 038ED811E76 for ; Wed, 25 Nov 2020 16:45:26 +0000 (UTC) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-587-5JyHE8CzMIukVk0S95TDWw-1; Wed, 25 Nov 2020 11:45:20 -0500 X-MC-Unique: 5JyHE8CzMIukVk0S95TDWw-1 Received: by verein.lst.de (Postfix, from userid 2407) id 05B8968B02; Wed, 25 Nov 2020 17:45:16 +0100 (CET) Date: Wed, 25 Nov 2020 17:45:15 +0100 From: Christoph Hellwig To: Tejun Heo Message-ID: <20201125164515.GB1975@lst.de> References: <20201124132751.3747337-1-hch@lst.de> <20201124132751.3747337-26-hch@lst.de> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-loop: dm-devel@redhat.com Cc: Jens Axboe , Jan Kara , Mike Snitzer , Konrad Rzeszutek Wilk , Greg Kroah-Hartman , Jan Kara , Josef Bacik , Coly Li , linux-block@vger.kernel.org, Richard Weinberger , dm-devel@redhat.com, linux-mtd@lists.infradead.org, linux-mm@kvack.org, Johannes Thumshirn , linux-fsdevel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org, Christoph Hellwig Subject: Re: [dm-devel] [PATCH 25/45] block: reference struct block_device from struct hd_struct X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, Nov 24, 2020 at 04:18:49PM -0500, Tejun Heo wrote: > Hello, > > Please see lkml.kernel.org/r/X708BTJ5njtbC2z1@mtj.duckdns.org for a few nits > on the previous version. Thanks, I've addressed the mapping_set_gfp mask nit and updated the commit log. As Jan pointed also pointed out I think we do need the remove_inode_hash. > I might be confused but am wondering whether RCU is needed. It's currently > used to ensure that gendisk is accessible in the blkdev_get path but > wouldn't it be possible to simply pin gendisk from block_devices? The > gendisk and hd_structs hold the base refs of the block_devices and in turn > the block_devices pin the gendisk. When the gendisk gets deleted, it puts > the base refs of the block devices but stays around while the block devices > are being accessed. Yes, that sounds sensible. I'll take a look. > Also, would it make sense to separate out lookup_sem removal? I *think* it's > there to ensure that the same bdev doesn't get associated with old and new > gendisks at the same time but can't wrap my head around how it works > exactly. I can see that this may not be needed once the lifetimes of gendisk > and block_devices are tied together but that may warrant a bit more > explanation. Jan added lookup_sem in commit 56c0908c855afbb to prevent a three way race between del_gendisk and blkdev_open due to the weird bdev vs gendisk lifetime rules. None of that can happen with the new lookup scheme. -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel