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 8968FC742D7 for ; Sat, 13 Jul 2019 13:20:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5881B2083B for ; Sat, 13 Jul 2019 13:20:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="LhMmDJex" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727839AbfGMNUH (ORCPT ); Sat, 13 Jul 2019 09:20:07 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:32916 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726474AbfGMNUG (ORCPT ); Sat, 13 Jul 2019 09:20:06 -0400 Received: by mail-pf1-f194.google.com with SMTP id g2so5512984pfq.0 for ; Sat, 13 Jul 2019 06:20:06 -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=t3ZLqWcrgfhZARjYVG38FnXLowWxYFGSUF90TwdQKak=; b=LhMmDJexwpmDvlUUqG9AZ0eqr/cR9BbdJh9N8GK2wc3brzk6sE81mzT865WRFJC5ig 4XoBn7Hao9QwObCiDCbQy5q+VsiGlhPQxgj7SKIf2Co5fnsByjhAdHXUUZCrT1kSpIWO nSTX+ekBk/4KuYgTvPGeRkgtTBGreqHZtjGRY1tNQNvzzo5yFedlkzbtgNYT1hZicUVz CJdQCUVpsnPDNRSmNILCWnrC1XFydlpAdLN/6yn/bp80DkTg9Qrqkbs+ul3JLHKknp+Q 7bJf6JDHG6Vtf05dIXwK5a44rMDmI6sAoRMvuSrJ9KH9nGC+fpuOYG9E5bH27x/nxWnK DPBw== 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=t3ZLqWcrgfhZARjYVG38FnXLowWxYFGSUF90TwdQKak=; b=o7FIj9UP9z6Nfysc1K4q7rEnAMSbxN2ZoMWMHoGDGstoOft6l3tkB4CW/kv+JGrpL3 XTxERccd9iD2DFzZlvcKOPUSfCMf6xUOUuIJQLDCiejpiBl9qkFjmAzHzA8AmSk3TsVb 2sphm3MjMsNjFi9trMmq16Tj6VfRA152uILRaP/syoLXML4wFGLgkIaRi3SMJFL0Dr6w G/lKCwwbVMJFphAVeq4yg69JxN/XTyKCeBNV0K14pIloiNp30S9qwj3lViSR9ssXG56k jCP7JE0D2jksoUiGnxIa1ZW87Z9FuwUbk8VF7l3+C4Xylm9KUYcFlSWfWJuPLXjHKtrP T65A== X-Gm-Message-State: APjAAAX1cMTsBndk4l98/IS51oF7+3KMJTd9kiW/NqQbCOfPBcJPDduZ Pjwq7kzrkWxkt+VuO2V8Gyo= X-Google-Smtp-Source: APXvYqyOee2O8F1rFI8E7UGw7sE8Lvg3la871hAMyIz1mfS4821xEZYdOCJlIJbUsCl7TPstC3rhnw== X-Received: by 2002:a63:f118:: with SMTP id f24mr17344644pgi.322.1563024005191; Sat, 13 Jul 2019 06:20:05 -0700 (PDT) Received: from localhost ([121.137.63.184]) by smtp.gmail.com with ESMTPSA id t29sm14383786pfq.156.2019.07.13.06.20.03 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sat, 13 Jul 2019 06:20:03 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Sat, 13 Jul 2019 22:19:47 +0900 To: Konstantin Khlebnikov Cc: Sergey Senozhatsky , Konstantin Khlebnikov , Petr Mladek , Linux Kernel Mailing List , Steven Rostedt Subject: Re: [PATCH] kernel/printk: prevent deadlock at calling kmsg_dump from NMI context Message-ID: <20190713131947.GA4464@tigerII.localdomain> References: <156294329676.1745.2620297516210526183.stgit@buzz> <20190713060929.GB1038@tigerII.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 (07/13/19 09:46), Konstantin Khlebnikov wrote: > > On (07/12/19 17:54), Konstantin Khlebnikov wrote: > > Yep printk() can deal with NMI, but kmsg_dump() is a different beast. > It reads printk buffer and saves content into persistent storage like ACPI ERST. Ah, sorry! I misread your patch. Yeah, I see what you are doing. OK. So, I guess that for kmsg_dump(KMSG_DUMP_PANIC) we should be fine in general. We call kmsg_dump(KMSG_DUMP_PANIC) after smp_send_stop() and after printk_safe_flush_on_panic(). printk_safe_flush_on_panic() resets the state of logbuf_lock, so logbuf_lock, in general case, should be unlocked by the time we call kmsg_dump(KMSG_DUMP_PANIC). Even for nested contexts. CPU0 printk() logbuf_lock_irqsave(flags) -> NMI panic() smp_send_stop() printk_safe_flush_on_panic() raw_spin_lock_init(&logbuf_lock) << reinit >> kmsg_dump(KMSG_DUMP_PANIC) logbuf_lock_irqsave(flags) << expected to be OK >> So do we have strong reasons to disable NMI->panic->kmsg_dump(DUMP_PANIC)? Other kmsg_dump(), maybe, can experience some troubles sometimes, need to check that. -ss