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 75DFEC433EF for ; Mon, 20 Jun 2022 04:47:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237899AbiFTErq (ORCPT ); Mon, 20 Jun 2022 00:47:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229908AbiFTEro (ORCPT ); Mon, 20 Jun 2022 00:47:44 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 68F1DDE8B; Sun, 19 Jun 2022 21:47:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fCr5yst88e9lOqfCL8d20AyDjixx1Tg4bKOmHaG5Jow=; b=CB7fZ7AWdEHyso1o/f+KTAvtct LpAuZ/vJN2PAKslW7c3JjUGbQZ0LDPxG4H/stpmRgfBfT5Jcf4B+pauHkDfLKtEoJB8zfxGyl3YlT WTW5R0VFufpOc8LsIN/XeVRUbzS2ThaEd6C1eZJvqjvZwk8X5sCORVr9UPyykDWItfvmRPQUluwzO gPMT+VPfarZYzTMA7AYFoGif0o9iV8ohWa6cYmtrxKRHmtblzYaIojoRc2FZ1ip98xax7GxHU9GyU wzyA5m2106PS6Ey5nYh8h5MJMRIIX49Xev2nT2tDv+tKn5EAU4+8ESZtOMq6O5YB5g+48y8xcn+Me oygBbQmg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1o39K4-004s1L-KZ; Mon, 20 Jun 2022 04:47:36 +0000 Date: Mon, 20 Jun 2022 05:47:36 +0100 From: Matthew Wilcox To: Miaohe Lin Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] filemap: obey mapping->invalidate_lock lock/unlock order Message-ID: References: <20220618083820.35626-1-linmiaohe@huawei.com> <364c8981-95c4-4bf8-cfbf-688c621db5b5@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <364c8981-95c4-4bf8-cfbf-688c621db5b5@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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, > 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! > > > > > . > > >