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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 20BD4C742A7 for ; Sat, 13 Jul 2019 06:09:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5D6D208E4 for ; Sat, 13 Jul 2019 06:09:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="HvNgtd9g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726649AbfGMGJt (ORCPT ); Sat, 13 Jul 2019 02:09:49 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:33135 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726301AbfGMGJt (ORCPT ); Sat, 13 Jul 2019 02:09:49 -0400 Received: by mail-pf1-f195.google.com with SMTP id g2so5245536pfq.0 for ; Fri, 12 Jul 2019 23:09:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=WqiGEOnvmZLw2GIPiVqeh/nsRYHRSwUYib+cvrcYRFQ=; b=HvNgtd9gFiHhIwb10R/md5MmTIj6pHpfdX82m4NLqmzWrHiLuIICBvz+hib1SqelGD b/Umj+pOgsrCjY0uzVLV9BxDmcHStDVxVXXAKUyB//IKo6gIvFeQPRoUEGLx61hzAQB2 aWtD47FH9vW/duP3nJ6NXplgA8w0KweGCyLImc0gp7BKndP/L5gfVNs+L0GPT8Ly/oHy 0fWUH3lnS1NY58uGYjaEYxUJEYstIA1VdiyLeRsMkCb17B6vFMSoaNecgi8XxI2Tx137 WJgOkJCumNOYwuU4qupgAb06o6zKs9JPmf/jr5iY2hhFVd93hnkLmoCUKv+74YTXsrFF kUgw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=WqiGEOnvmZLw2GIPiVqeh/nsRYHRSwUYib+cvrcYRFQ=; b=Y6vVXaeFfAhyvV/SzYuf+Ysc/vfVBqQkRNByeaomf4D0b6oYTGNINl+B+NV9miHpC7 4MVCBVTSvLri/TnETu9ld0sLfBvkCQONMS7dCZNjhpB7T+UTlBqq9/Glz3G/hTkKSz3T sDq/wnPE6sbKGd7XCumnaORvqsFkH937uievqXucjrBPt2sLIP5yBLRi+5c3+JL9zPEK MRMJ80NwKoXbd5A323abaNg3YrahwiJSz0hMfmB+LKX3OHYdTZuv8HbLLu6uGXoFC9MW Uoi7JZNWKr/CdIGjGfmysh9QeejqGg47f+zrKBVOdodvRhzhDbdHj4G3o4igPtAx5Ue2 URIQ== X-Gm-Message-State: APjAAAVFkY8ZehgJxlJw2DsjrE37fhT21irj/OBIKsBb27vQPFeEFuyp d5NvQDmn4blvRxdjSRodWIPePvK9 X-Google-Smtp-Source: APXvYqxkUQe/qy3Z0u0zS64PlAL9G0t7p/OQieqiMZ9Jaw4qJii+0Qyl5p89u0CaChhV/+8BEUqpBQ== X-Received: by 2002:a17:90a:3ac2:: with SMTP id b60mr16790954pjc.74.1562998188303; Fri, 12 Jul 2019 23:09:48 -0700 (PDT) Received: from localhost ([121.137.63.184]) by smtp.gmail.com with ESMTPSA id g6sm9397370pgh.64.2019.07.12.23.09.46 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 12 Jul 2019 23:09:47 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Sat, 13 Jul 2019 15:09:29 +0900 To: Konstantin Khlebnikov Cc: Petr Mladek , linux-kernel@vger.kernel.org, Steven Rostedt , Sergey Senozhatsky Subject: Re: [PATCH] kernel/printk: prevent deadlock at calling kmsg_dump from NMI context Message-ID: <20190713060929.GB1038@tigerII.localdomain> References: <156294329676.1745.2620297516210526183.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <156294329676.1745.2620297516210526183.stgit@buzz> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (07/12/19 17:54), Konstantin Khlebnikov wrote: > Function kmsg_dump could be invoked from NMI context intentionally or > accidentally because it is called at various oops/panic paths. > Kernel message dumpers are not ready to work in NMI context right now. > They could deadlock on lockbuf_lock or break internal structures. Hmm. printk()-s from NMI go through per-CPU printk_safe/nmi - a bunch of lockless buffers which is supposed to deal with printk() deadlocks, including NMI printk()-s. include/linux/hardirq.h #define nmi_enter() ... printk_nmi_enter(); ... #define nmi_exit() ... printk_nmi_exit(); ... So we are not really supposed to deadlock. -ss