From patchwork Thu Apr 21 11:48:43 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Petr Mladek X-Patchwork-Id: 613075 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3qrHB711Yjz9s5Q for ; Thu, 21 Apr 2016 21:50:23 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751591AbcDULtR (ORCPT ); Thu, 21 Apr 2016 07:49:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:42552 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752194AbcDULtP (ORCPT ); Thu, 21 Apr 2016 07:49:15 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 4BAF2AD91; Thu, 21 Apr 2016 11:49:10 +0000 (UTC) From: Petr Mladek To: Andrew Morton Cc: Peter Zijlstra , Steven Rostedt , Russell King , Daniel Thompson , Jiri Kosina , Ingo Molnar , Thomas Gleixner , Sergey Senozhatsky , Chris Metcalf , linux-kernel@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, adi-buildroot-devel@lists.sourceforge.net, linux-cris-kernel@axis.com, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Petr Mladek , Jan Kara , Ralf Baechle , Benjamin Herrenschmidt , Martin Schwidefsky , David Miller Subject: [PATCH v5 2/4] printk/nmi: warn when some message has been lost in NMI context Date: Thu, 21 Apr 2016 13:48:43 +0200 Message-Id: <1461239325-22779-3-git-send-email-pmladek@suse.com> X-Mailer: git-send-email 1.8.5.6 In-Reply-To: <1461239325-22779-1-git-send-email-pmladek@suse.com> References: <1461239325-22779-1-git-send-email-pmladek@suse.com> Sender: sparclinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: sparclinux@vger.kernel.org We could not resize the temporary buffer in NMI context. Let's warn if a message is lost. This is rather theoretical. printk() should not be used in NMI. The only sensible use is when we want to print backtrace from all CPUs. The current buffer should be enough for this purpose. [akpm@linux-foundation.org: whitespace fixlet] Signed-off-by: Petr Mladek Cc: Jan Kara Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Russell King Cc: Daniel Thompson Cc: Jiri Kosina Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Ralf Baechle Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: David Miller Cc: Daniel Thompson Signed-off-by: Andrew Morton --- kernel/printk/internal.h | 11 +++++++++++ kernel/printk/nmi.c | 5 ++++- kernel/printk/printk.c | 10 ++++++++++ 3 files changed, 25 insertions(+), 1 deletion(-) diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 2de99faedfc1..341bedccc065 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -34,6 +34,12 @@ static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) return this_cpu_read(printk_func)(fmt, args); } +extern atomic_t nmi_message_lost; +static inline int get_nmi_message_lost(void) +{ + return atomic_xchg(&nmi_message_lost, 0); +} + #else /* CONFIG_PRINTK_NMI */ static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) @@ -41,4 +47,9 @@ static inline __printf(1, 0) int vprintk_func(const char *fmt, va_list args) return vprintk_default(fmt, args); } +static inline int get_nmi_message_lost(void) +{ + return 0; +} + #endif /* CONFIG_PRINTK_NMI */ diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c index 303cf0d15e57..572f94922230 100644 --- a/kernel/printk/nmi.c +++ b/kernel/printk/nmi.c @@ -39,6 +39,7 @@ */ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; static int printk_nmi_irq_ready; +atomic_t nmi_message_lost; #define NMI_LOG_BUF_LEN (4096 - sizeof(atomic_t) - sizeof(struct irq_work)) @@ -64,8 +65,10 @@ static int vprintk_nmi(const char *fmt, va_list args) again: len = atomic_read(&s->len); - if (len >= sizeof(s->buffer)) + if (len >= sizeof(s->buffer)) { + atomic_inc(&nmi_message_lost); return 0; + } /* * Make sure that all old data have been read before the buffer was diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 71eba0607034..e38579d730f4 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1617,6 +1617,7 @@ asmlinkage int vprintk_emit(int facility, int level, unsigned long flags; int this_cpu; int printed_len = 0; + int nmi_message_lost; bool in_sched = false; /* cpu currently holding logbuf_lock in this function */ static unsigned int logbuf_cpu = UINT_MAX; @@ -1667,6 +1668,15 @@ asmlinkage int vprintk_emit(int facility, int level, strlen(recursion_msg)); } + nmi_message_lost = get_nmi_message_lost(); + if (unlikely(nmi_message_lost)) { + text_len = scnprintf(textbuf, sizeof(textbuf), + "BAD LUCK: lost %d message(s) from NMI context!", + nmi_message_lost); + printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0, + NULL, 0, textbuf, text_len); + } + /* * The printf needs to come first; we need the syslog * prefix which might be passed-in as a parameter.