From nobody Mon May 11 04:11:51 2026 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 104B3C433EF for ; Fri, 15 Apr 2022 00:01:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347795AbiDOADV (ORCPT ); Thu, 14 Apr 2022 20:03:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240890AbiDOADS (ORCPT ); Thu, 14 Apr 2022 20:03:18 -0400 Received: from out1.migadu.com (out1.migadu.com [IPv6:2001:41d0:2:863f::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2221254FB2 for ; Thu, 14 Apr 2022 17:00:51 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1649980849; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=SAPfxf3f9RbNYZ744rn1YiJP6Q/ipIgNaszXOZfmBmM=; b=sIzXJ4P4SnwfNi9HuU0cj4oUqn/hycVugErFuVEc3JNrdjWXEbeBASykM7+T/Pmt9gjVD+ RgwH1/S6WnZRVQm77Ucu4IpVW+79MHuzW25qVuekoK8ROGtazQMKb5ziUWL1zaIgGF733G OfNgyef6346bbYvFKDWz8ixC2mRyhnI= From: Naoya Horiguchi To: Matthew Wilcox , linux-mm@kvack.org Cc: Christoph Hellwig , Andrew Morton , John Hubbard , Jason Gunthorpe , William Kucharski , Naoya Horiguchi , linux-kernel@vger.kernel.org Subject: [PATCH v1] mm: recheck PageCompound() before printing out info of head page Date: Fri, 15 Apr 2022 08:59:50 +0900 Message-Id: <20220414235950.840409-1-naoya.horiguchi@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Naoya Horiguchi The following VM_BUG_ON_FOLIO() is triggered when memory error event happens on the (thp/folio) pages which are about to be freed: [ 1160.232771] page:00000000b36a8a0f refcount:1 mapcount:0 mapping:000000= 0000000000 index:0x1 pfn:0x16a000 [ 1160.236916] page:00000000b36a8a0f refcount:0 mapcount:0 mapping:000000= 0000000000 index:0x1 pfn:0x16a000 [ 1160.240684] flags: 0x57ffffc0800000(hwpoison|node=3D1|zone=3D2|lastcpu= pid=3D0x1fffff) [ 1160.243458] raw: 0057ffffc0800000 dead000000000100 dead000000000122 00= 00000000000000 [ 1160.246268] raw: 0000000000000001 0000000000000000 00000000ffffffff 00= 00000000000000 [ 1160.249197] page dumped because: VM_BUG_ON_FOLIO(!folio_test_large(fol= io)) [ 1160.251815] ------------[ cut here ]------------ [ 1160.253438] kernel BUG at include/linux/mm.h:788! [ 1160.256162] invalid opcode: 0000 [#1] PREEMPT SMP PTI [ 1160.258172] CPU: 2 PID: 115368 Comm: mceinj.sh Tainted: G E= 5.18.0-rc1-v5.18-rc1-220404-2353-005-g83111+ #3 [ 1160.262049] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO= S 1.15.0-1.fc35 04/01/2014 [ 1160.265103] RIP: 0010:dump_page.cold+0x27e/0x2bd [ 1160.266757] Code: fe ff ff 48 c7 c6 81 f1 5a 98 e9 4c fe ff ff 48 c7 c= 6 a1 95 59 98 e9 40 fe ff ff 48 c7 c6 50 bf 5a 98 48 89 ef e8 9d 04 6d ff <= 0f> 0b 41 f7 c4 ff 0f 00 00 0f 85 9f fd ff ff 49 8b 04 24 a9 00 00 [ 1160.273180] RSP: 0018:ffffaa2c4d59fd18 EFLAGS: 00010292 [ 1160.274969] RAX: 000000000000003e RBX: 0000000000000001 RCX: 000000000= 0000000 [ 1160.277263] RDX: 0000000000000001 RSI: ffffffff985995a1 RDI: 00000000f= fffffff [ 1160.279571] RBP: ffffdc9c45a80000 R08: 0000000000000000 R09: 00000000f= fffdfff [ 1160.281794] R10: ffffaa2c4d59fb08 R11: ffffffff98940d08 R12: ffffdc9c4= 5a80000 [ 1160.283920] R13: ffffffff985b6f94 R14: 0000000000000000 R15: ffffdc9c4= 5a80000 [ 1160.286641] FS: 00007eff54ce1740(0000) GS:ffff99c67bd00000(0000) knlG= S:0000000000000000 [ 1160.289498] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1160.291106] CR2: 00005628381a5f68 CR3: 0000000104712003 CR4: 000000000= 0170ee0 [ 1160.293031] Call Trace: [ 1160.293724] [ 1160.294334] get_hwpoison_page+0x47d/0x570 [ 1160.295474] memory_failure+0x106/0xaa0 [ 1160.296474] ? security_capable+0x36/0x50 [ 1160.297524] hard_offline_page_store+0x43/0x80 [ 1160.298684] kernfs_fop_write_iter+0x11c/0x1b0 [ 1160.299829] new_sync_write+0xf9/0x160 [ 1160.300810] vfs_write+0x209/0x290 [ 1160.301835] ksys_write+0x4f/0xc0 [ 1160.302718] do_syscall_64+0x3b/0x90 [ 1160.303664] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 1160.304981] RIP: 0033:0x7eff54b018b7 As shown in the RIP address, this VM_BUG_ON in folio_entire_mapcount() is called from dump_page("hwpoison: unhandlable page") in get_any_page(). The below explains the mechanism of the race: CPU 0 CPU 1 memory_failure get_hwpoison_page get_any_page dump_page compound =3D PageCompound free_pages_prepare page->flags &=3D ~PAGE_FL= AGS_CHECK_AT_PREP folio_entire_mapcount VM_BUG_ON_FOLIO(!folio_test_large(folio)) So in order to avoid the BUG_ON, recheck PageCompound() before __dump_page() prints out information about the head page. Precisely saying, this does not close up the race, but mitigates the impact to just inaccurate info, which should be acceptable. Fixes: 74e8ee4708a8 ("mm: Turn head_compound_mapcount() into folio_entire_m= apcount()") Signed-off-by: Naoya Horiguchi --- I'm actually not sure how widely the race condition could affect. If we can consider this as a bug specific to memory_failure(), simply replacing the dump_page() with simple printk() might be a proper fix (I confirmed that that fix also works). But if any other dump_page()'s caller could race with freeing thp/folio, the more generic fix (I'm suggesting in this patch) would be desirable. --- mm/debug.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/debug.c b/mm/debug.c index bef329bf28f0..fce63b200bea 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -93,7 +93,7 @@ static void __dump_page(struct page *page) pr_warn("page:%p refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n= ", page, page_ref_count(head), mapcount, mapping, page_to_pgoff(page), page_to_pfn(page)); - if (compound) { + if (compound && PageCompound(page)) { pr_warn("head:%p order:%u compound_mapcount:%d compound_pincount:%d\n", head, compound_order(head), folio_entire_mapcount(folio), --=20 2.25.1