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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3952DC43334 for ; Mon, 20 Jun 2022 12:14:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A38E76B0071; Mon, 20 Jun 2022 08:14:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9E98E8E0002; Mon, 20 Jun 2022 08:14:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8B1268E0001; Mon, 20 Jun 2022 08:14:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 7861B6B0071 for ; Mon, 20 Jun 2022 08:14:30 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 34B4320F2F for ; Mon, 20 Jun 2022 12:14:30 +0000 (UTC) X-FDA: 79598507100.22.F34DE72 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf24.hostedemail.com (Postfix) with ESMTP id EFCD0180017 for ; Mon, 20 Jun 2022 12:14:20 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4LRT7N6YBKzkWZ0; Mon, 20 Jun 2022 20:13:04 +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 20:14:15 +0800 Subject: Re: [PATCH] filemap: obey mapping->invalidate_lock lock/unlock order To: Muchun Song CC: Matthew Wilcox , , , , References: <20220618083820.35626-1-linmiaohe@huawei.com> <364c8981-95c4-4bf8-cfbf-688c621db5b5@huawei.com> <72315fc0-eee9-13c8-2d94-43c8c7045a91@huawei.com> From: Miaohe Lin Message-ID: <385dcf89-da4c-d3ac-333a-7ab40ecbdf9f@huawei.com> Date: Mon, 20 Jun 2022 20:14:14 +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: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655727269; a=rsa-sha256; cv=none; b=XjBukNrMLle1Pnsn9hXBLv16cU076dxBdwFGLZUBVHxLqOW8+jt4LFJswa16x8wAPZY+eY wdw94w5evpFHm6GgNUmTnBLs7XfWTtW4ueCJp5z8knSPyYM73CxZ4epWbBxE+N8k63SwD/ TTLhleLnhpliYeP5kVfEAsJ2xyQ8hmY= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf24.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655727269; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=84JNfelCkdxLToTDsvreDCjZT6RVwreOH7JGiyTrztY=; b=WCQYhllZ0/ZpxjViQLGTHLHKmypXjQiPOaLeWgYOEV0mEoG35FqEb52xS6cPbUyW5KDa6W jJ5hx3g5Aokz9dC1tjUcj03zbtbI5G+cHoeyR92AIo6LHF926UXPBht5ehP3kH5YVEFLFs +wK9EHRPRmvmVx95G+H8Fa+bbYiFGJg= Authentication-Results: imf24.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf24.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: pqghjigyqzihrzknpe5u9kax577uixd7 X-Rspamd-Queue-Id: EFCD0180017 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1655727260-433492 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/6/20 17:47, Muchun Song wrote: > On Mon, Jun 20, 2022 at 02:35:30PM +0800, Miaohe Lin wrote: >> 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? >> > > lock(A) lock(B) unlock(A) unlock(B) is fine. So it is better not to complicate the code. Yes, it seems the gain is not worth complicating the code. So I will drop the patch. Thanks. > >> 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! >>>> >>>>> >>>>> . >>>>> >>>> >>> >>> . >>> >> >> > . >