From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: + printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch added to -mm tree Date: Thu, 21 Apr 2016 15:04:02 -0700 Message-ID: <57194e52.Q6tu760hCJ7nOaWK%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:58801 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbcDUWEE (ORCPT ); Thu, 21 Apr 2016 18:04:04 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: pmladek@suse.com, benh@kernel.crashing.org, daniel.thompson@linaro.org, davem@davemloft.net, jack@suse.cz, jkosina@suse.com, mingo@redhat.com, peterz@infradead.org, ralf@linux-mips.org, rmk+kernel@arm.linux.org.uk, rostedt@goodmis.org, schwidefsky@de.ibm.com, tglx@linutronix.de, mm-commits@vger.kernel.org The patch titled Subject: printk/nmi: warn when some message has been lost in NMI context has been added to the -mm tree. Its filename is printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Petr Mladek Subject: printk/nmi: warn when some message has been lost in NMI context 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 -puN kernel/printk/internal.h~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context kernel/printk/internal.h --- a/kernel/printk/internal.h~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context +++ a/kernel/printk/internal.h @@ -34,6 +34,12 @@ static inline __printf(1, 0) int vprintk 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 return vprintk_default(fmt, args); } +static inline int get_nmi_message_lost(void) +{ + return 0; +} + #endif /* CONFIG_PRINTK_NMI */ diff -puN kernel/printk/nmi.c~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context kernel/printk/nmi.c --- a/kernel/printk/nmi.c~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context +++ a/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, 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 -puN kernel/printk/printk.c~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context kernel/printk/printk.c --- a/kernel/printk/printk.c~printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context +++ a/kernel/printk/printk.c @@ -1617,6 +1617,7 @@ asmlinkage int vprintk_emit(int facility 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 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. _ Patches currently in -mm which might be from pmladek@suse.com are printk-nmi-generic-solution-for-safe-printk-in-nmi.patch printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch printk-nmi-increase-the-size-of-nmi-buffer-and-make-it-configurable.patch printk-nmi-flush-nmi-messages-on-the-system-panic.patch