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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6029C25B07 for ; Fri, 5 Aug 2022 17:31:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241407AbiHERa6 (ORCPT ); Fri, 5 Aug 2022 13:30:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241307AbiHERag (ORCPT ); Fri, 5 Aug 2022 13:30:36 -0400 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB3471CFCC for ; Fri, 5 Aug 2022 10:30:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1659720627; x=1691256627; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=2dM1WuVb6OYAaV0IBScAMcULpTf1F1saRBlYGODMl4Y=; b=O5NQFTmWrIh3RahCydOgJk4XM95UBTpl1FJzoA2lIfaeXtzKEqJZim0Y R99n+uoeLEnIBj9hLQCqjjBrCiyYPzwAoYiyvpHt5sN3PTPh/M1I7M5lJ dnH+am/nvT1wVZ7OecFSNyuyQBCDoSn8T0Mz97uM4l8Kk/vLVhQm8Hk0j ANFbj9PRCZnjGFKc62+ZZSZ25H09b9FceMULrN4w6YaMPozUw/He6zj/K KLThPCnZlVxievzZ8T/NTuCZHW492AWBHA6E9X+VtshR2+D+EFAjMdzNz D9lAc/3nAn8WQgYDzjSbl6MTHL8MX1DP9JI3Z7585aLoMgzVlpFkRUseX Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10430"; a="270634129" X-IronPort-AV: E=Sophos;i="5.93,216,1654585200"; d="scan'208";a="270634129" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2022 10:30:27 -0700 X-IronPort-AV: E=Sophos;i="5.93,216,1654585200"; d="scan'208";a="706678695" Received: from amecham-mobl.amr.corp.intel.com (HELO localhost) ([10.255.0.242]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Aug 2022 10:30:26 -0700 From: ira.weiny@intel.com To: Rik van Riel , Borislav Petkov , Dave Hansen Cc: Dave Jones , x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [RFC PATCH 4/5] x86,mm: print likely CPU at segfault time Date: Fri, 5 Aug 2022 10:30:08 -0700 Message-Id: <20220805173009.3128098-5-ira.weiny@intel.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20220805173009.3128098-1-ira.weiny@intel.com> References: <20220805173009.3128098-1-ira.weiny@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel In a large enough fleet of computers, it is common to have a few bad CPUs. Those can often be identified by seeing that some commonly run kernel code, which runs fine everywhere else, keeps crashing on the same CPU core on one particular bad system. However, the failure modes in CPUs that have gone bad over the years are often oddly specific, and the only bad behavior seen might be segfaults in programs like bash, python, or various system daemons that run fine everywhere else. Add a printk() to show_signal_msg() to print the CPU, core, and socket at segfault time. This is not perfect, since the task might get rescheduled on another CPU between when the fault hit, and when the message is printed, but in practice this has been good enough to help us identify several bad CPU cores. segfault[1349]: segfault at 0 ip 000000000040113a sp 00007ffc6d32e360 error 4 in segfault[401000+1000] on CPU 0 (core 0, socket 0) This printk can be controlled through /proc/sys/debug/exception-trace Signed-off-by: Rik van Riel CC: Dave Jones --- arch/x86/mm/fault.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 971977c438fc..82cf23975aa1 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -769,6 +769,8 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code, unsigned long address, struct task_struct *tsk) { const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; + /* This is a racy snapshot, but it's better than nothing. */ + int cpu = raw_smp_processor_id(); if (!unhandled_signal(tsk, SIGSEGV)) return; @@ -782,6 +784,14 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code, print_vma_addr(KERN_CONT " in ", regs->ip); + /* + * Dump the likely CPU where the fatal segfault happened. + * This can help identify faulty hardware. + */ + printk(KERN_CONT " on CPU %d (core %d, socket %d)", cpu, + topology_core_id(cpu), topology_physical_package_id(cpu)); + + printk(KERN_CONT "\n"); show_opcodes(regs, loglvl); -- 2.35.3