From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752833AbbLKNWj (ORCPT ); Fri, 11 Dec 2015 08:22:39 -0500 Received: from mx2.suse.de ([195.135.220.15]:48201 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751094AbbLKNUy (ORCPT ); Fri, 11 Dec 2015 08:20:54 -0500 From: Petr Mladek To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, Geert Uytterhoeven , Arnd Bergmann , jkosina@suse.com, pmladek@suse.com Subject: [PATCH v4 3/4] printk/nmi: Warn when some message has been lost in NMI context Date: Fri, 11 Dec 2015 14:20:51 +0100 Message-Id: <1449840052-10491-4-git-send-email-pmladek@suse.com> X-Mailer: git-send-email 1.8.5.6 In-Reply-To: <1449840052-10491-1-git-send-email-pmladek@suse.com> References: <1449840052-10491-1-git-send-email-pmladek@suse.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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. 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 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 9a506bd18b9d..d86f55cccf31 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 480ad05ab299..71183a308b9e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1669,6 +1669,7 @@ 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; @@ -1719,6 +1720,15 @@ 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. -- 1.8.5.6