From: Christoph Hellwig Subject: Re: [RFC PATCH 1/3] Implement generic freeze feature Date: Mon, 28 Apr 2008 06:37:19 -0400 Message-ID: <20080428103719.GA16030@infradead.org> References: <20080428193123t-sato@mail.jp.nec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "linux-ext4@vger.kernel.org" , "xfs@oss.sgi.com" , "dm-devel@redhat.com" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Takashi Sato Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:43806 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755301AbYD1KhU (ORCPT ); Mon, 28 Apr 2008 06:37:20 -0400 Content-Disposition: inline In-Reply-To: <20080428193123t-sato@mail.jp.nec.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Apr 28, 2008 at 07:31:23PM +0900, Takashi Sato wrote: > + /* Initialize semaphore for freeze. */ > + sema_init(&bdev->bd_freeze_sem, 1); The freezing process is already protected by bd_mount_sem, so I don't think there's need for another one. > --- linux-2.6.25.org/fs/buffer.c 2008-04-17 11:49:44.000000000 +0900 > +++ linux-2.6.25-freeze/fs/buffer.c 2008-04-24 20:43:28.000000000 +0900 > @@ -201,6 +201,19 @@ struct super_block *freeze_bdev(struct b > { > struct super_block *sb; > > + down(&bdev->bd_freeze_sem); > + sb = get_super_without_lock(bdev); > + > + /* If super_block has been already frozen, return. */ > + if (sb && sb->s_frozen != SB_UNFROZEN) { > + put_super(sb); > + up(&bdev->bd_freeze_sem); > + return sb; > + } > + > + if (sb) > + put_super(sb); > + > down(&bdev->bd_mount_sem); > sb = get_super(bdev); I think the protection against double freezes would be better done by using a trylock on bd_mount_sem. In fact after that it could be changed from a semaphore to a simple test_and_set_bit. > error = -ENOTTY; > break; > + > + case FIFREEZE: { This would be better to split intot a small helper ala ioctl_fibmap() > + case FITHAW: { Same here.