From: Christoph Hellwig Subject: Re: [PATCH 1/3] Implement generic freeze feature Date: Mon, 8 Sep 2008 13:10:26 -0400 Message-ID: <20080908171020.GA22521@infradead.org> References: <20080908205245t-sato@mail.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Christoph Hellwig , Oleg Nesterov , "linux-fsdevel@vger.kernel.org" , "dm-devel@redhat.com" , "viro@ZenIV.linux.org.uk" , "linux-ext4@vger.kernel.org" , "xfs@oss.sgi.com" , "axboe@kernel.dk" , "mtk.manpages@googlemail.com" , "linux-kernel@vger.kernel.org" To: Takashi Sato Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:52360 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751767AbYIHRKf (ORCPT ); Mon, 8 Sep 2008 13:10:35 -0400 Content-Disposition: inline In-Reply-To: <20080908205245t-sato@mail.jp.nec.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Sep 08, 2008 at 08:52:45PM +0900, Takashi Sato wrote: > diff -uprN -X linux-2.6.27-rc5.org/Documentation/dontdiff linux-2.6.27-rc5.org/fs/block_dev.c linux-2.6.27-rc5-freeze/fs > /block_dev.c > --- linux-2.6.27-rc5.org/fs/block_dev.c 2008-08-29 07:52:02.000000000 +0900 > +++ linux-2.6.27-rc5-freeze/fs/block_dev.c 2008-09-05 20:00:29.000000000 +0900 > @@ -285,6 +285,8 @@ static void init_once(void *foo) > INIT_LIST_HEAD(&bdev->bd_holder_list); > #endif > inode_init_once(&ei->vfs_inode); > + /* Initialize mutex for freeze. */ > + mutex_init(&bdev->bd_fsfreeze_mutex); Why not just freeze_mutex? > struct super_block *freeze_bdev(struct block_device *bdev) > { > struct super_block *sb; > > + mutex_lock(&bdev->bd_fsfreeze_mutex); > + if (bdev->bd_fsfreeze_count > 0) { > + bdev->bd_fsfreeze_count++; > + sb = get_super(bdev); > + mutex_unlock(&bdev->bd_fsfreeze_mutex); > + return sb; > + } > + bdev->bd_fsfreeze_count++; > + > down(&bdev->bd_mount_sem); Note that we still have duplication with the bd_mount_sem. I think you should look into getting rid of it and instead do a check of the freeze_count under proper freeze_mutex protection. > +int thaw_bdev(struct block_device *bdev, struct super_block *sb) > { > + mutex_lock(&bdev->bd_fsfreeze_mutex); > + if (!bdev->bd_fsfreeze_count) { > + mutex_unlock(&bdev->bd_fsfreeze_mutex); > + return 0; > + } > + > + bdev->bd_fsfreeze_count--; > + if (bdev->bd_fsfreeze_count > 0) { > + if (sb) > + drop_super(sb); > + mutex_unlock(&bdev->bd_fsfreeze_mutex); > + return 0; > + } > + > if (sb) { > BUG_ON(sb->s_bdev != bdev); > > @@ -244,6 +274,8 @@ void thaw_bdev(struct block_device *bdev > } > > up(&bdev->bd_mount_sem); > + mutex_unlock(&bdev->bd_fsfreeze_mutex); > + return 0; Why do you add a return value here if we always return 0 anyway?