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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 BC559C43387 for ; Wed, 16 Jan 2019 09:43:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8960420859 for ; Wed, 16 Jan 2019 09:43:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391814AbfAPJnr convert rfc822-to-8bit (ORCPT ); Wed, 16 Jan 2019 04:43:47 -0500 Received: from tyo161.gate.nec.co.jp ([114.179.232.161]:52939 "EHLO tyo161.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731808AbfAPJnr (ORCPT ); Wed, 16 Jan 2019 04:43:47 -0500 X-Greylist: delayed 623 seconds by postgrey-1.27 at vger.kernel.org; Wed, 16 Jan 2019 04:43:45 EST Received: from mailgate01.nec.co.jp ([114.179.233.122]) by tyo161.gate.nec.co.jp (8.15.1/8.15.1) with ESMTPS id x0G9X4BV021404 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 16 Jan 2019 18:33:04 +0900 Received: from mailsv01.nec.co.jp (mailgate-v.nec.co.jp [10.204.236.94]) by mailgate01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x0G9X45g021398; Wed, 16 Jan 2019 18:33:04 +0900 Received: from mail01b.kamome.nec.co.jp (mail01b.kamome.nec.co.jp [10.25.43.2]) by mailsv01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x0G9WWcY000507; Wed, 16 Jan 2019 18:33:04 +0900 Received: from bpxc99gp.gisp.nec.co.jp ([10.38.151.152] [10.38.151.152]) by mail01b.kamome.nec.co.jp with ESMTP id BT-MMP-1507344; Wed, 16 Jan 2019 18:30:47 +0900 Received: from BPXM23GP.gisp.nec.co.jp ([10.38.151.215]) by BPXC24GP.gisp.nec.co.jp ([10.38.151.152]) with mapi id 14.03.0319.002; Wed, 16 Jan 2019 18:30:47 +0900 From: Naoya Horiguchi To: Dan Williams , Andrew Morton , "linux-mm@kvack.org" CC: Jane Chu , linux-nvdimm , Linux Kernel Mailing List Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig() (Re: PMEM error-handling forces SIGKILL causes kernel panic) Thread-Topic: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig() (Re: PMEM error-handling forces SIGKILL causes kernel panic) Thread-Index: AQHUrX4o7Slk8dv5sk2r4phfic2oGA== Date: Wed, 16 Jan 2019 09:30:46 +0000 Message-ID: <20190116093046.GA29835@hori1.linux.bs1.fc.nec.co.jp> References: <20190111081401.GA5080@hori1.linux.bs1.fc.nec.co.jp> In-Reply-To: <20190111081401.GA5080@hori1.linux.bs1.fc.nec.co.jp> Accept-Language: en-US, ja-JP Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.51.8.80] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ CCed Andrew and linux-mm ] On Fri, Jan 11, 2019 at 08:14:02AM +0000, Horiguchi Naoya(堀口 直也) wrote: > Hi Dan, Jane, > > Thanks for the report. > > On Wed, Jan 09, 2019 at 03:49:32PM -0800, Dan Williams wrote: > > [ switch to text mail, add lkml and Naoya ] > > > > On Wed, Jan 9, 2019 at 12:19 PM Jane Chu wrote: > ... > > > 3. The hardware consists the latest revision CPU and Intel NVDIMM, we suspected > > > the CPU faulty because it generated MCE over PMEM UE in a unlikely high > > > rate for any reasonable NVDIMM (like a few per 24hours). > > > > > > After swapping the CPU, the problem stopped reproducing. > > > > > > But one could argue that perhaps the faulty CPU exposed a small race window > > > from collect_procs() to unmap_mapping_range() and to kill_procs(), hence > > > caught the kernel PMEM error handler off guard. > > > > There's definitely a race, and the implementation is buggy as can be > > seen in __exit_signal: > > > > sighand = rcu_dereference_check(tsk->sighand, > > lockdep_tasklist_lock_is_held()); > > spin_lock(&sighand->siglock); > > > > ...the memory-failure path needs to hold the proper locks before it > > can assume that de-referencing tsk->sighand is valid. > > > > > Also note, the same workload on the same faulty CPU were run on Linux prior to > > > the 4.19 PMEM error handling and did not encounter kernel crash, probably because > > > the prior HWPOISON handler did not force SIGKILL? > > > > Before 4.19 this test should result in a machine-check reboot, not > > much better than a kernel crash. > > > > > Should we not to force the SIGKILL, or find a way to close the race window? > > > > The race should be closed by holding the proper tasklist and rcu read lock(s). > > This reasoning and proposal sound right to me. I'm trying to reproduce > this race (for non-pmem case,) but no luck for now. I'll investigate more. I wrote/tested a patch for this issue. I think that switching signal API effectively does proper locking. Thanks, Naoya Horiguchi --- >From 16dbf6105ff4831f73276d79d5df238ab467de76 Mon Sep 17 00:00:00 2001 From: Naoya Horiguchi Date: Wed, 16 Jan 2019 16:59:27 +0900 Subject: [PATCH] mm: hwpoison: use do_send_sig_info() instead of force_sig() Currently memory_failure() is racy against process's exiting, which results in kernel crash by null pointer dereference. The root cause is that memory_failure() uses force_sig() to forcibly kill asynchronous (meaning not in the current context) processes. As discussed in thread https://lkml.org/lkml/2010/6/8/236 years ago for OOM fixes, this is not a right thing to do. OOM solves this issue by using do_send_sig_info() as done in commit d2d393099de2 ("signal: oom_kill_task: use SEND_SIG_FORCED instead of force_sig()"), so this patch is suggesting to do the same for hwpoison. do_send_sig_info() properly accesses to siglock with lock_task_sighand(), so is free from the reported race. I confirmed that the reported bug reproduces with inserting some delay in kill_procs(), and it never reproduces with this patch. Note that memory_failure() can send another type of signal using force_sig_mceerr(), and the reported race shouldn't happen on it because force_sig_mceerr() is called only for synchronous processes (i.e. BUS_MCEERR_AR happens only when some process accesses to the corrupted memory.) Reported-by: Jane Chu Cc: Dan Williams Cc: stable@vger.kernel.org Signed-off-by: Naoya Horiguchi --- mm/memory-failure.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 7c72f2a95785..831be5ff5f4d 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -372,7 +372,8 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail, if (fail || tk->addr_valid == 0) { pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n", pfn, tk->tsk->comm, tk->tsk->pid); - force_sig(SIGKILL, tk->tsk); + do_send_sig_info(SIGKILL, SEND_SIG_PRIV, + tk->tsk, PIDTYPE_PID); } /* -- 2.7.5