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=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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 5D0CFC4363A for ; Fri, 30 Oct 2020 12:08:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBF8C221E2 for ; Fri, 30 Oct 2020 12:08:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Wmzq52Ka" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726527AbgJ3MI0 (ORCPT ); Fri, 30 Oct 2020 08:08:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:53376 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726413AbgJ3MIY (ORCPT ); Fri, 30 Oct 2020 08:08:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604059702; h=from:from: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=KxlJ8Mwn0Tke0WPb8nHZ6w8mEJXEo5j2Z00nnV/ApfQ=; b=Wmzq52KaSQ1+YGSIS2RnmLNb3RBhkISIVRfYUkZD3drb5hVPL6ZHSLaIkwEkzC6f4AtRzv u8PSSLINt2sRK0NDCAf1TwxjGErLbPeBJoIzfgqiDrq1xDxXkNzyNmZId1gffnhcKflG/a cOlYaXdcNwOyNPQV1iNDqQFVsqN0Gjo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-50-AzIfXLJtNRSF2-f3T9HVoQ-1; Fri, 30 Oct 2020 08:08:18 -0400 X-MC-Unique: AzIfXLJtNRSF2-f3T9HVoQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1A88A101F000; Fri, 30 Oct 2020 12:08:17 +0000 (UTC) Received: from ovpn-66-212.rdu2.redhat.com (ovpn-66-212.rdu2.redhat.com [10.10.66.212]) by smtp.corp.redhat.com (Postfix) with ESMTP id F238219C71; Fri, 30 Oct 2020 12:08:15 +0000 (UTC) Message-ID: Subject: Re: kernel BUG at mm/page-writeback.c:2241 [ BUG_ON(PageWriteback(page); ] From: Qian Cai To: Matthew Wilcox Cc: Christoph Hellwig , "Darrick J. Wong" , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , linux-mm@kvack.org Date: Fri, 30 Oct 2020 08:08:15 -0400 In-Reply-To: <20201022171243.GX20115@casper.infradead.org> References: <645a3f332f37e09057c10bc32f4f298ce56049bb.camel@lca.pw> <20201022004906.GQ20115@casper.infradead.org> <7ec15e2710db02be81a6c47afc57abed4bf8016c.camel@lca.pw> <20201022171243.GX20115@casper.infradead.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, 2020-10-22 at 18:12 +0100, Matthew Wilcox wrote: > On Thu, Oct 22, 2020 at 11:35:26AM -0400, Qian Cai wrote: > > On Thu, 2020-10-22 at 01:49 +0100, Matthew Wilcox wrote: > > > On Wed, Oct 21, 2020 at 08:30:18PM -0400, Qian Cai wrote: > > > > Today's linux-next starts to trigger this wondering if anyone has any > > > > clue. > > > > > > I've seen that occasionally too. I changed that BUG_ON to VM_BUG_ON_PAGE > > > to try to get a clue about it. Good to know it's not the THP patches > > > since they aren't in linux-next. > > > > > > I don't understand how it can happen. We have the page locked, and then > > > we > > > do: > > > > > > if (PageWriteback(page)) { > > > if (wbc->sync_mode != WB_SYNC_NONE) > > > wait_on_page_writeback(page); > > > else > > > goto continue_unlock; > > > } > > > > > > VM_BUG_ON_PAGE(PageWriteback(page), page); > > > > > > Nobody should be able to put this page under writeback while we have it > > > locked ... right? The page can be redirtied by the code that's supposed > > > to be writing it back, but I don't see how anyone can make PageWriteback > > > true while we're holding the page lock. > > > > It happened again on today's linux-next: > > > > [ 7613.579890][T55770] page:00000000a4b35e02 refcount:3 mapcount:0 > > mapping:00000000457ceb87 index:0x3e pfn:0x1cef4e > > [ 7613.590594][T55770] aops:xfs_address_space_operations ino:805d85a dentry > > name:"doio.f1.55762" > > [ 7613.599192][T55770] flags: > > 0xbfffc0000000bf(locked|waiters|referenced|uptodate|dirty|lru|active) > > [ 7613.608596][T55770] raw: 00bfffc0000000bf ffffea0005027d48 > > ffff88810eaec030 ffff888231f3a6a8 > > [ 7613.617101][T55770] raw: 000000000000003e 0000000000000000 > > 00000003ffffffff ffff888143724000 > > [ 7613.625590][T55770] page dumped because: > > VM_BUG_ON_PAGE(PageWriteback(page)) > > [ 7613.632695][T55770] page->mem_cgroup:ffff888143724000 > > Seems like it reproduces for you pretty quickly. I have no luck ;-( > > Can you add this? It turns out I had no luck for the last a few days. I'll keep running and report back if it triggers again. > > +++ b/mm/page-writeback.c > @@ -2774,6 +2774,7 @@ int __test_set_page_writeback(struct page *page, bool > keep_write) > struct address_space *mapping = page_mapping(page); > int ret, access_ret; > > + VM_BUG_ON_PAGE(!PageLocked(page), page); > lock_page_memcg(page); > if (mapping && mapping_use_writeback_tags(mapping)) { > XA_STATE(xas, &mapping->i_pages, page_index(page)); > > This is the only place (afaict) that sets PageWriteback, so that will > tell us whether someone is setting Writeback without holding the lock, > or whether we're suffering from a spurious wakeup. >