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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 445FAC43219 for ; Sat, 27 Apr 2019 15:26:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A301206A3 for ; Sat, 27 Apr 2019 15:26:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728109AbfD0P0C (ORCPT ); Sat, 27 Apr 2019 11:26:02 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:34822 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727408AbfD0PZ6 (ORCPT ); Sat, 27 Apr 2019 11:25:58 -0400 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1hKP3B-0000z8-1b; Sat, 27 Apr 2019 16:15:37 +0100 Received: from ben by deadeye with local (Exim 4.92) (envelope-from ) id 1hKP2i-0004Rf-IR; Sat, 27 Apr 2019 16:15:08 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Vineet Gupta" Date: Sat, 27 Apr 2019 16:13:09 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 051/202] ARC: mm: do_page_fault fixes #1: relinquish mmap_sem if signal arrives while handle_mm_fault In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.66-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Vineet Gupta commit 4d447455e73b47c43dd35fcc38ed823d3182a474 upstream. do_page_fault() forgot to relinquish mmap_sem if a signal came while handling handle_mm_fault() - due to say a ctl+c or oom etc. This would later cause a deadlock by acquiring it twice. This came to light when running libc testsuite tst-tls3-malloc test but is likely also the cause for prior seen LTP failures. Using lockdep clearly showed what the issue was. | # while true; do ./tst-tls3-malloc ; done | Didn't expect signal from child: got `Segmentation fault' | ^C | ============================================ | WARNING: possible recursive locking detected | 4.17.0+ #25 Not tainted | -------------------------------------------- | tst-tls3-malloc/510 is trying to acquire lock: | 606c7728 (&mm->mmap_sem){++++}, at: __might_fault+0x28/0x5c | |but task is already holding lock: |606c7728 (&mm->mmap_sem){++++}, at: do_page_fault+0x9c/0x2a0 | | other info that might help us debug this: | Possible unsafe locking scenario: | | CPU0 | ---- | lock(&mm->mmap_sem); | lock(&mm->mmap_sem); | | *** DEADLOCK *** | ------------------------------------------------------------ What the change does is not obvious (note to myself) prior code was | do_page_fault | | down_read() <-- lock taken | handle_mm_fault <-- signal pending as this runs | if fatal_signal_pending | if VM_FAULT_ERROR | up_read | if user_mode | return <-- lock still held, this was the BUG New code | do_page_fault | | down_read() <-- lock taken | handle_mm_fault <-- signal pending as this runs | if fatal_signal_pending | if VM_FAULT_RETRY | return <-- not same case as above, but still OK since | core mm already relinq lock for FAULT_RETRY | ... | | < Now falls through for bug case above > | | up_read() <-- lock relinquished Signed-off-by: Vineet Gupta [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- arch/arc/mm/fault.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) --- a/arch/arc/mm/fault.c +++ b/arch/arc/mm/fault.c @@ -131,12 +131,17 @@ good_area: */ fault = handle_mm_fault(mm, vma, address, flags); - /* If Pagefault was interrupted by SIGKILL, exit page fault "early" */ if (unlikely(fatal_signal_pending(current))) { - if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY)) - up_read(&mm->mmap_sem); - if (user_mode(regs)) + + /* + * if fault retry, mmap_sem already relinquished by core mm + * so OK to return to user mode (with signal handled first) + */ + if (fault & VM_FAULT_RETRY) { + if (!user_mode(regs)) + goto no_context; return; + } } if (likely(!(fault & VM_FAULT_ERROR))) {