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 0AF6DC43334 for ; Tue, 5 Jul 2022 23:39:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3F5DC8E0002; Tue, 5 Jul 2022 19:39:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3A2978E0001; Tue, 5 Jul 2022 19:39:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 26B478E0002; Tue, 5 Jul 2022 19:39:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 134058E0001 for ; Tue, 5 Jul 2022 19:39:04 -0400 (EDT) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id D7A1860CAA for ; Tue, 5 Jul 2022 23:39:03 +0000 (UTC) X-FDA: 79654664166.19.CBA675D Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf16.hostedemail.com (Postfix) with ESMTP id 9D6BC180025 for ; Tue, 5 Jul 2022 23:39:02 +0000 (UTC) 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=7dOROrO9ycYqqFp5LnucNCHf+IZBjlMW0xOCXAdstaI=; b=SH/FIVKv4ze5KjxElB8DD+inAv WdgdA14/H/bwLYy5QM/Kru16CyPUMnpZ+eg35afyOs5VvA4c7xWgYmI8Nx9YO12eNeJqwzH45+qTr dHJcvlOSkhByWy8WIj0WctzuLSc+wZfi2mhShSWc/U6kDWohGRVQfpjj0irNXCCBFxSkoeTtuNfAR sMnsK0WTTuTqdIEOCmlQbyxp8vlUEbcQIjFBTj2Dlz0/ivW7eHjSry8gjEQOw2nKpAPqTRuJ2oJd5 +2a1PjbuHoa08mVoKksM3iFz7LHK/1/kCuK7wIkfMK0Pw7DRhpA/Z/ik0lh87lWBSpoCu6HGi1i0a RJmKoX8g==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1o8s7t-0010o7-IO; Tue, 05 Jul 2022 23:38:41 +0000 Date: Wed, 6 Jul 2022 00:38:41 +0100 From: Matthew Wilcox To: Andrew Morton Cc: Muchun Song , jgg@ziepe.ca, jhubbard@nvidia.com, william.kucharski@oracle.com, dan.j.williams@intel.com, jack@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v2] mm: fix missing wake-up event for FSDAX pages Message-ID: References: <20220705123532.283-1-songmuchun@bytedance.com> <20220705141819.804eb972d43be3434dc70192@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220705141819.804eb972d43be3434dc70192@linux-foundation.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657064343; a=rsa-sha256; cv=none; b=Cj66HCiSB4QPoxraqIuG2/TwuR9nxHUdkIa+TUJxwICLaCEZUDvLA5RLJdlh0I9X94aqBt eDT3ena6zfML2+x90mIfjm3nNbk4eqiBHNL7iF0IWTXuzL4s02OwKg1SbRpIgutnngvLMw PrezykQK6B409PHSwaZkhAODryaCQb8= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="SH/FIVKv"; dmarc=none; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657064343; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=7dOROrO9ycYqqFp5LnucNCHf+IZBjlMW0xOCXAdstaI=; b=IFMf5943Uw+1uWnRA2j3UtH/C34a/RDGtuk1IJXmUU86i9DpGbfF770Rhu6IGXDjZESXq2 QB/Vr6uCJSobb2n0WdIA1ugrMzp+Fh4YSS1mXOEnS4DZDwaTxZDc8DF35mHA1ZpUHwFTso JMbv6/rkGzcRFn18oOTtxGyg0WngeoI= Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="SH/FIVKv"; dmarc=none; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Stat-Signature: ezjuj1pe6ep4dqr7irrsuw4q1adaphzk X-Rspamd-Queue-Id: 9D6BC180025 X-Rspamd-Server: rspam05 X-Rspam-User: X-HE-Tag: 1657064342-256953 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 Tue, Jul 05, 2022 at 02:18:19PM -0700, Andrew Morton wrote: > On Tue, 5 Jul 2022 20:35:32 +0800 Muchun Song wrote: > > > FSDAX page refcounts are 1-based, rather than 0-based: if refcount is > > 1, then the page is freed. The FSDAX pages can be pinned through GUP, > > then they will be unpinned via unpin_user_page() using a folio variant > > to put the page, however, folio variants did not consider this special > > case, the result will be to miss a wakeup event (like the user of > > __fuse_dax_break_layouts()). Since FSDAX pages are only possible get > > by GUP users, so fix GUP instead of folio_put() to lower overhead. > > > > What are the user visible runtime effects of this bug? "missing wake up event" seems pretty obvious to me? Something goes to sleep waiting for a page to become unused, and is never woken.