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 8F1C9C4332F for ; Sun, 13 Nov 2022 16:44:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0E2408E0003; Sun, 13 Nov 2022 11:44:58 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 090E38E0002; Sun, 13 Nov 2022 11:44:58 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9A248E0003; Sun, 13 Nov 2022 11:44:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id DA4598E0002 for ; Sun, 13 Nov 2022 11:44:57 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id A6A0A1A0932 for ; Sun, 13 Nov 2022 16:44:57 +0000 (UTC) X-FDA: 80128993434.27.5FF3D05 Received: from mail-oa1-f44.google.com (mail-oa1-f44.google.com [209.85.160.44]) by imf18.hostedemail.com (Postfix) with ESMTP id 4DBA61C0007 for ; Sun, 13 Nov 2022 16:44:57 +0000 (UTC) Received: by mail-oa1-f44.google.com with SMTP id 586e51a60fabf-13bef14ea06so10314738fac.3 for ; Sun, 13 Nov 2022 08:44:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=tOaqCckFi7nd+3f5dDf1x4jA/0HIMYHcjdK95GwU2xk=; b=PRigsovIiMk8XCfk1xXxHZBYX6WXhPxABJVn7oXt2VTJoNycu40ozSjTKizoZI4Fgi iPwylg/msPm1UtM3mZrywi24OUGAaIFGcNjXug+bs9m2ZD9x+2Z/cYuQ9/K6oNTSxAPv XbZPRdJG79TY4OBOnqdDEhaTK5MX0UqE7lgotcyzUQ5iQUJo2fheMDBDzPenT4HyulhY PA/l9XQa30ucn91BqVJz/IwCUr1YHA/o9ND5UvtjRNt6q6S3gJkoDGSZez9UDP1tC5tF aluTzLy0d4feyan3jx5ypeImoFaXed1CroXmwmk7MvaFf5w5O9kd0o8geFVhwTauq+4z 3oCg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=tOaqCckFi7nd+3f5dDf1x4jA/0HIMYHcjdK95GwU2xk=; b=iuBnEEc1YyUk9ePNa5rQxnpnhXLvfYH50vsbMKIPLPXa9SymAc4yRoXrfvjHGDlBOP 2YmS74pT92m6A9lHepRXMTWuJmO6Trj9lMasCbgFa14twh4FPH+YaRTHmRfdnxEVrdli Spl137Z2W73jq45T8Iet9NMUcDJ+COtkGIO6jXimg9JTgiRCKQwj2NeTW4xVii2A+uFy RpWQizLg/xQCV28od0mUSXWj5gTAreLGDzS//3QbPYIbfN0mmIP5wIehJEv7Cy+MCSko WT/3dWX4S18jk7CT7JvNfsnNipLJHttxMb53ctfbpyv63rBAuZUrt9F0pFKTulZCM2j0 Z+lw== X-Gm-Message-State: ANoB5pmjkqD+d1xkOhogDnWck/elQz87v8Gjy5OuJ39RBUHvIQgeqgV0 mkpYF4hoj2FmstIZhi4Znj8lhjIUQco23esd+c7EiQ== X-Google-Smtp-Source: AA0mqf7WYMuZJ+mQYr7+rjv7+rZUo6v6UfqkYnYLWEpS5+eo5laQupp3efgJWg7yXF/SNwvpAKdZ75jxQvZThHTd9Fg= X-Received: by 2002:a05:6870:1117:b0:13d:a22b:3503 with SMTP id 23-20020a056870111700b0013da22b3503mr5220927oaf.233.1668357896154; Sun, 13 Nov 2022 08:44:56 -0800 (PST) MIME-Version: 1.0 References: <000000000000aa2b2805ebea9137@google.com> <9a450a11-531d-8e1a-4c77-70102aa7f424@redhat.com> In-Reply-To: From: Dmitry Vyukov Date: Sun, 13 Nov 2022 17:44:45 +0100 Message-ID: Subject: Re: [syzbot] WARNING in __split_huge_page_tail To: Hugh Dickins Cc: David Hildenbrand , syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, Mel Gorman Content-Type: text/plain; charset="UTF-8" ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668357897; 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=tOaqCckFi7nd+3f5dDf1x4jA/0HIMYHcjdK95GwU2xk=; b=kVP7h3WuhLJJNFk70KKO4ze/Z9boXa98EDNVJR8QBe47UFa5EKq1/9J0wkkE152umTKfPW 9cHdODpx44FfjWi5kpWtiEno/MofvWjxEWYI9c5Yxbc+hPG4CXWaps9q+CLjDmjPExeZZ+ S0GTyXr824y3SlqV36CBB5mLn9g9euM= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=PRigsovI; spf=pass (imf18.hostedemail.com: domain of dvyukov@google.com designates 209.85.160.44 as permitted sender) smtp.mailfrom=dvyukov@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668357897; a=rsa-sha256; cv=none; b=Fr77/tm8U5mtTCTIVxjOgdms7uW5KG3Oe7iGeQ9qzIN/218g6vDVivT/CQsDuPqLr86e/I MzCSa2EP1U6hiUbPo45LEskfoN/uNfrjsErYYa/QuPVHpyJ+qb8OtJGbwp5Df947Hzsa9H LreIP4KpFUPxqJydagMh5En6GH4+hyg= X-Stat-Signature: 3pgfidkfi9rrahsynaztpz41w1e1y4t1 X-Rspamd-Queue-Id: 4DBA61C0007 Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=PRigsovI; spf=pass (imf18.hostedemail.com: domain of dvyukov@google.com designates 209.85.160.44 as permitted sender) smtp.mailfrom=dvyukov@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam07 X-Rspam-User: X-HE-Tag: 1668357897-607525 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 Wed, 26 Oct 2022 at 18:18, Hugh Dickins wrote: > > >> On 26.10.22 08:59, syzbot wrote: > > >>> Hello, > > >>> > > >>> syzbot found the following issue on: > > >>> > > >>> HEAD commit: 4da34b7d175d Merge tag 'thermal-6.1-rc2' of > > >>> git://git.kern.. > > >>> git tree: upstream > > >>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=113bd8bc880000 > > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=4789759e8a6d5f57 > > >>> dashboard link: > > >>> https://syzkaller.appspot.com/bug?extid=273b547b15eb58ea35e8 > > >>> compiler: Debian clang version > > >>> 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU > > >>> Binutils for Debian) 2.35.2 > > >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=161e1f62880000 > > >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16dd4fe6880000 > > >>> > > >>> Downloadable assets: > > >>> disk image: > > >>> https://storage.googleapis.com/syzbot-assets/a61ddb36c296/disk-4da34b7d.raw.xz > > >>> vmlinux: > > >>> https://storage.googleapis.com/syzbot-assets/ceee41246252/vmlinux-4da34b7d.xz > > >>> > > >>> IMPORTANT: if you fix the issue, please add the following tag to the > > >>> commit: > > >>> Reported-by: syzbot+273b547b15eb58ea35e8@syzkaller.appspotmail.com > > >>> > > >>> tlb_finish_mmu+0xcb/0x200 mm/mmu_gather.c:363 > > >>> exit_mmap+0x2b1/0x670 mm/mmap.c:3098 > > >>> __mmput+0x114/0x3b0 kernel/fork.c:1185 > > >>> exit_mm+0x217/0x2f0 kernel/exit.c:516 > > >>> do_exit+0x5e7/0x2070 kernel/exit.c:807 > > >>> do_group_exit+0x1fd/0x2b0 kernel/exit.c:950 > > >>> __do_sys_exit_group kernel/exit.c:961 [inline] > > >>> __se_sys_exit_group kernel/exit.c:959 [inline] > > >>> __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:959 > > >>> do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > >>> do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80 > > >>> entry_SYSCALL_64_after_hwframe+0x63/0xcd > > >>> ------------[ cut here ]------------ > > >>> WARNING: CPU: 0 PID: 3908 at mm/huge_memory.c:2465 > > >>> __split_huge_page_tail+0x81c/0x1080 mm/huge_memory.c:2465 > > >> > > >> Is this the > > >> > > >> VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail); > > >> > > >> assertion? > > > > > > Hi David, > > > > > > You can check the sources for that revision, but on the dashboard > > > there are clickable links for all source references: > > > https://syzkaller.appspot.com/bug?extid=273b547b15eb58ea35e8 > > > > > > In this case it points to: > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/huge_memory.c?id=4da34b7d175dc99b8befebd69e96546c960d526c#n2465 > > > > > > > Ah, thanks! > > > > ... so > > > > if (!folio_test_swapcache(page_folio(head))) { > > VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, head); > > page_tail->private = 0; > > } > > > > I recall that there was a patch either from Hugh or Mel floating around that > > might be related. > > Yes, it's in akpm's mm-hotfixes-unstable branch, currently at > 826367c8c422 ("mm: prep_compound_tail() clear page->private") Let's tell syzbot about the fix so that it reports similar bugs in future: #syz fix: mm: prep_compound_tail() clear page->private > [PATCH] mm: prep_compound_tail() clear page->private > > Although page allocation always clears page->private in the first page > or head page of an allocation, it has never made a point of clearing > page->private in the tails (though 0 is often what is already there). > > But now commit 71e2d666ef85 ("mm/huge_memory: do not clobber swp_entry_t > during THP split") issues a warning when page_tail->private is found to > be non-0 (unless it's swapcache). > > Change that warning to dump page_tail (which also dumps head), instead > of just the head: so far we have seen dead000000000122, dead000000000003, > dead000000000001 or 0000000000000002 in the raw output for tail private. > > We could just delete the warning, but today's consensus appears to want > page->private to be 0, unless there's a good reason for it to be set: > so now clear it in prep_compound_tail() (more general than just for THP; > but not for high order allocation, which makes no pass down the tails). > > Fixes: 71e2d666ef85 ("mm/huge_memory: do not clobber swp_entry_t during THP split") > Signed-off-by: Hugh Dickins > Cc: Mel Gorman > Cc: Matthew Wilcox (Oracle) > Cc: > --- > mm/huge_memory.c | 2 +- > mm/page_alloc.c | 1 + > 2 files changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 03fc7e5edf07..561a42567477 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2462,7 +2462,7 @@ static void __split_huge_page_tail(struct page *head, int tail, > * Fix up and warn once if private is unexpectedly set. > */ > if (!folio_test_swapcache(page_folio(head))) { > - VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, head); > + VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail); > page_tail->private = 0; > } > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index b5a6c815ae28..218b28ee49ed 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -807,6 +807,7 @@ static void prep_compound_tail(struct page *head, int tail_idx) > > p->mapping = TAIL_MAPPING; > set_compound_head(p, head); > + set_page_private(p, 0); > } > > void prep_compound_page(struct page *page, unsigned int order) > -- > 2.35.3