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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38452C43462 for ; Thu, 8 Apr 2021 14:51:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F1A6261108 for ; Thu, 8 Apr 2021 14:51:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231963AbhDHOvh (ORCPT ); Thu, 8 Apr 2021 10:51:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57030 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231370AbhDHOvf (ORCPT ); Thu, 8 Apr 2021 10:51:35 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 30640C061760; Thu, 8 Apr 2021 07:51:23 -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=+cewsqIjy3KyilGPYnpep4bhBTgpsrNatr9SSgJPp+A=; b=Xq6rS14iEtk33sZT1twqc2gQB0 jTafc881dELFdZxc453Afl84KSiCv9BlDNWFMmnJqrJ7+pawRB2ciuCtRFt6kKI+67dnyH1Vd/aA7 7recD+wKVjyEya+hf36HVxPE0dSKP9CBNHdVCkNzZWKcJpH/ZJ2zX25TtfW/6NVV1IjRtxvZ+Y3Kf /g0OXDI4v3N1ArJHE3LwyaVlOjJjpbQQ8+YtWS2daRZRHbFa6TRRt+0A3Y+zpZh/i8glAZMVgyLPP PhwAcASqyaMDlSOzGFxhq/JZ5fYkxv2Mq+XkfA5VgxX/Xx+g4UBo2NUNNibb8nZFuAboaixfLddhj uGQILrJg==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lUVzl-00GNO2-Ap; Thu, 08 Apr 2021 14:51:03 +0000 Date: Thu, 8 Apr 2021 15:50:57 +0100 From: Matthew Wilcox To: David Howells Cc: linux-fsdevel@vger.kernel.org, Linus Torvalds , Alexander Viro , Christoph Hellwig , linux-mm@kvack.org, linux-cachefs@redhat.com, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Jeff Layton , David Wysochanski , linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private_2 Message-ID: <20210408145057.GN2531743@casper.infradead.org> References: <161789062190.6155.12711584466338493050.stgit@warthog.procyon.org.uk> <161789066013.6155.9816857201817288382.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <161789066013.6155.9816857201817288382.stgit@warthog.procyon.org.uk> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 08, 2021 at 03:04:20PM +0100, David Howells wrote: > +static inline void set_page_private_2(struct page *page) > +{ > + get_page(page); > + SetPagePrivate2(page); PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY) So we can set Private2 on any tail page ... > +void end_page_private_2(struct page *page) > +{ > + page = compound_head(page); > + VM_BUG_ON_PAGE(!PagePrivate2(page), page); > + clear_bit_unlock(PG_private_2, &page->flags); > + wake_up_page_bit(page, PG_private_2); ... but when we try to end on a tail, we actually wake up the head ... > +void wait_on_page_private_2(struct page *page) > +{ > + while (PagePrivate2(page)) > + wait_on_page_bit(page, PG_private_2); ... although if we were waiting on a tail, the wake up won't find us ... if only we had a way to ensure this kind of bug can't happen *cough, lend your support to the page folio patches*.