From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3399165-1526625507-2-1511392024916420440 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, FREEMAIL_FORGED_FROMDOMAIN 0.248, FREEMAIL_FROM 0.001, HEADER_FROM_DIFFERENT_DOMAINS 0.248, MAILING_LIST_MULTI -1, RCVD_IN_DNSWL_HI -5, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='com', MailFrom='org' X-Spam-charsets: plain='us-ascii' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=fm2; t= 1526625507; b=IC1/LFwEPVtCCwFiPaTlNmtZ4TYo9+thzAZoIxSXnrNmNNAA65 IOnT0g/3VVmftSqBdv2hMxL+yqR7U0XeEWbEKfFJWLrx50EG0EkL1ZZvDrr9V+3h +B0U3iNQzehTjdiy6jz990eB/+l++35Q4mrFYNp1CSt6I1o+jgvyOif2iSVnrCfU 5muJF2AaIjUEKXphT/edPCxOFCxEGMC/QbwwbmlZre8dYnC85rEip7WLnLjgPzFB H1G0CWxZrO0NguinNN1+cOSpb3bLNmWmZ7WcHH4Mwnr4BKl1sSFpugVZz0E1hvuT 5txuh6xbVzHguOaovk8ar8l6o4gW2Frgd8Qw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=date:from:to:cc:subject:message-id :references:mime-version:content-type:in-reply-to:sender :list-id; s=fm2; t=1526625507; bh=sPxk8ad+7/Fd8NSt9iGruJ/y24LJwE qxgZogkRg93Mg=; b=eVig8JXZo570DPkHrPjF5twDRCcbhfldgvNSFI1/4KjYs7 3PJsSwhPrK8RadCAABZYMm0QzU/7/e+cAb19CqgiOR3xTsJrgMUA0DcuMfcBOGym H5RMgS78ZjNUfqQsTPBquHHcwHs82WZDzPNujlfY+iWaLFe5T65z68bi7DpT2jO1 WZI8g+/eOZ25ovheMuSmOPeaJiBrrFuLMx+EKjSur3UeKONMVSu5toVnn5vusCCp 8ifv7baqPV1LqSICu8wuvQt16J2T5hueqeR0d1yUY226CFVPym0lzaz5lLyED1uI 10NT3Ba/fY9/F90SOkX63vynBguLfyIYxXIeZ5Lg== ARC-Authentication-Results: i=1; mx5.messagingengine.com; arc=none (no signatures found); dkim=pass (2048-bit rsa key sha256) header.d=gmail.com header.i=@gmail.com header.b=S1pUB2xu x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=20161025; dmarc=pass (p=none,has-list-id=yes,d=none) header.from=gmail.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-google-dkim=pass (2048-bit rsa key) header.d=1e100.net header.i=@1e100.net header.b=CvgmkrsH; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=gmail.com header.result=pass header_is_org_domain=yes; x-vs=clean score=-85 state=0 Authentication-Results: mx5.messagingengine.com; arc=none (no signatures found); dkim=pass (2048-bit rsa key sha256) header.d=gmail.com header.i=@gmail.com header.b=S1pUB2xu x-bits=2048 x-keytype=rsa x-algorithm=sha256 x-selector=20161025; dmarc=pass (p=none,has-list-id=yes,d=none) header.from=gmail.com; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-google-dkim=pass (2048-bit rsa key) header.d=1e100.net header.i=@1e100.net header.b=CvgmkrsH; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=gmail.com header.result=pass header_is_org_domain=yes; x-vs=clean score=-85 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfKNja07b+mov8Qkdy73MBN5GsS+rmVB7ptp78SaSxZSzp6zt5R25PBXkoHTOPy1JbAaN5B++5r14KYOrmJ/mz8gGRcnE/yXTWyMqsdCZPVA7oNPyEU6k ZXJf0iQMpodzvOtvJTiViTBdkz9oKcl5uCV6vfwpxmMCgyP3r4+qd8PSdqNb3zxhIRIn3cKN4pSxRdVr0H7Q57yS4vpH2HSft8AJTRxL8iLPbpAYg0fhChal X-CM-Analysis: v=2.3 cv=NPP7BXyg c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=kj9zAlcOel0A:10 a=x7bEGLp0ZPQA:10 a=_cTQiL8xM1sA:10 a=VUJBJC2UJ8kA:10 a=JMeKj0A-FjpNQDL__pwA:9 a=DcSgj6W29Kz2PKby:21 a=Nh-2Odm_7ph4n8_t:21 a=CjuIK1q_8ugA:10 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751452AbeERGiZ (ORCPT ); Fri, 18 May 2018 02:38:25 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:44940 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751221AbeERGiZ (ORCPT ); Fri, 18 May 2018 02:38:25 -0400 X-Google-Smtp-Source: AB8JxZo3/KON+VqW9lg3jAQOyyeVBH5XudSQwd3TiKUF+pq6tNo5KzqgoQCtXKc7F68JYCyvWQ39mQ== Date: Fri, 18 May 2018 15:38:20 +0900 From: Sergey Senozhatsky To: Sergey Senozhatsky Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Peter Zijlstra , Tetsuo Handa , linux-kernel@vger.kernel.org, "4 . 13+" Subject: Re: [PATCH] printk/nmi: Prevent deadlock when serializing NMI backtraces Message-ID: <20180518063820.GA1504@jagdpanzerIV> References: <20180517143903.19339-1-pmladek@suse.com> <20180518020705.GB1160@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180518020705.GB1160@jagdpanzerIV> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On (05/18/18 11:07), Sergey Senozhatsky wrote: > > if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK) || > raw_spin_is_locked(&logbuf_lock) > > just to check per-CPU `printk_context' first and only afterwards > access the global `logbuf_lock'. printk_nmi_enter() happens on > every CPU, so maybe we can avoid some overhead by checking the > local per-CPU data first. Nah, may be it won't. This, probably, would have been the case if we had continue to call console drivers from printk_safe section [at least]. CPUs don't spend that much time in printk_safe sections. -ss