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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86252C433EF for ; Mon, 20 Jun 2022 06:35:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238562AbiFTGfk (ORCPT ); Mon, 20 Jun 2022 02:35:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56688 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230121AbiFTGfi (ORCPT ); Mon, 20 Jun 2022 02:35:38 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6882F64DA; Sun, 19 Jun 2022 23:35:33 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LRKc13zVtzkWP5; Mon, 20 Jun 2022 14:33:53 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 20 Jun 2022 14:35:31 +0800 Subject: Re: [PATCH] filemap: obey mapping->invalidate_lock lock/unlock order To: Matthew Wilcox CC: , , , References: <20220618083820.35626-1-linmiaohe@huawei.com> <364c8981-95c4-4bf8-cfbf-688c621db5b5@huawei.com> From: Miaohe Lin Message-ID: <72315fc0-eee9-13c8-2d94-43c8c7045a91@huawei.com> Date: Mon, 20 Jun 2022 14:35:30 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/20 12:47, Matthew Wilcox wrote: > On Mon, Jun 20, 2022 at 09:56:06AM +0800, Miaohe Lin wrote: >> On 2022/6/18 18:34, Matthew Wilcox wrote: >>> On Sat, Jun 18, 2022 at 04:38:20PM +0800, Miaohe Lin wrote: >>>> The invalidate_locks of two mappings should be unlocked in reverse order >>>> relative to the locking order in filemap_invalidate_lock_two(). Modifying >>> >>> Why? It's perfectly valid to lock(A) lock(B) unlock(A) unlock(B). >>> If it weren't we'd have lockdep check it and complain. It seems I misunderstand your word. I thought you said it must be at lock(A) lock(B) unlock(A) unlock(B) order... Sorry. >> >> For spin_lock, they are lock(A) lock(B) unlock(B) unlock(A) e.g. in copy_huge_pud, > > I think you need to spend some time thinking about the semantics of > locks and try to figure out why it would make any difference at all > which order locks (of any type) are _unlocked_ in, IIUC, the lock orders are important to prevent possible deadlock. But unlock orders should be relaxed because they won't result in problem indeed. And what I advocate here is that making it at lock(A) lock(B) unlock(B) unlock(A) order should be a better program practice. Or unlock order shouldn't be obligatory at practice? Thanks. > >> copy_huge_pmd, move_huge_pmd and so on: >> dst_ptl = pmd_lock(dst_mm, dst_pmd); >> src_ptl = pmd_lockptr(src_mm, src_pmd); >> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); >> ... >> spin_unlock(src_ptl); >> spin_unlock(dst_ptl); >> >> For rw_semaphore, they are also lock(A) lock(B) unlock(B) unlock(A) e.g. in dup_mmap(): >> mmap_write_lock_killable(oldmm) >> mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING); >> ... >> mmap_write_unlock(mm); >> mmap_write_unlock(oldmm); >> >> and ntfs_extend_mft(): >> down_write(&ni->file.run_lock); >> down_write_nested(&sbi->used.bitmap.rw_lock, BITMAP_MUTEX_CLUSTERS); >> ... >> up_write(&sbi->used.bitmap.rw_lock); >> up_write(&ni->file.run_lock); >> >> But I see some lock(A) lock(B) unlock(A) unlock(B) examples in some fs codes. Could you >> please tell me the right lock/unlock order? I'm somewhat confused now... >> >> BTW: If lock(A) lock(B) unlock(A) unlock(B) is requested, filemap_invalidate_lock_two might >> still need to be changed to respect that order? >> >> Thanks! >> >>> >>> . >>> >> > > . >