From: Christoph Hellwig Subject: Re: [RFC PATCH 1/3] Implement generic freeze feature Date: Sun, 25 May 2008 15:32:11 -0400 Message-ID: <20080525193211.GA24328@infradead.org> References: <20080522175020t-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: Content-Disposition: inline In-Reply-To: <20080522175020t-sato@mail.jp.nec.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org > + if (test_and_set_bit(BD_FREEZE_OP, &bdev->bd_state)) > + return ERR_PTR(-EBUSY); > + > + sb = get_super_without_lock(bdev); > + > + /* If super_block has been already frozen, return. */ > + if (sb && sb->s_frozen != SB_UNFROZEN) { > + put_super(sb); > + clear_bit(BD_FREEZE_OP, &bdev->bd_state); > + return sb; > + } The BD_FREEZE_OP flag in the block_device already prevents multiple freezes for a singe block device, so there is no need for this additional check and the get_super_without_lock helper. > down(&bdev->bd_mount_sem); And with that flag bd_mount_sem is also obsolete for preventing the multiple freeze operations. We still need investigate what synchronization we need vs unmount which also takes bd_mount_sem without every having document what it exactly protects.