Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753860AbaG3MUR (ORCPT ); Wed, 30 Jul 2014 08:20:17 -0400 Received: from ip4-83-240-18-248.cust.nbox.cz ([83.240.18.248]:36792 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753032AbaG3MPe (ORCPT ); Wed, 30 Jul 2014 08:15:34 -0400 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Tony Luck , Steven Rostedt , Jiri Slaby Subject: [PATCH 3.12 84/94] tracing: Fix wraparound problems in "uptime" trace clock Date: Wed, 30 Jul 2014 14:15:13 +0200 Message-Id: <9d9959cba3c983232a6cd6edda05dc86d24c981a.1406722270.git.jslaby@suse.cz> X-Mailer: git-send-email 2.0.1 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tony Luck 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 58d4e21e50ff3cc57910a8abc20d7e14375d2f61 upstream. The "uptime" trace clock added in: commit 8aacf017b065a805d27467843490c976835eb4a5 tracing: Add "uptime" trace clock that uses jiffies has wraparound problems when the system has been up more than 1 hour 11 minutes and 34 seconds. It converts jiffies to nanoseconds using: (u64)jiffies_to_usecs(jiffy) * 1000ULL but since jiffies_to_usecs() only returns a 32-bit value, it truncates at 2^32 microseconds. An additional problem on 32-bit systems is that the argument is "unsigned long", so fixing the return value only helps until 2^32 jiffies (49.7 days on a HZ=1000 system). Avoid these problems by using jiffies_64 as our basis, and not converting to nanoseconds (we do convert to clock_t because user facing API must not be dependent on internal kernel HZ values). Link: http://lkml.kernel.org/p/99d63c5bfe9b320a3b428d773825a37095bf6a51.1405708254.git.tony.luck@intel.com Fixes: 8aacf017b065 "tracing: Add "uptime" trace clock that uses jiffies" Signed-off-by: Tony Luck Signed-off-by: Steven Rostedt Signed-off-by: Jiri Slaby --- kernel/trace/trace.c | 2 +- kernel/trace/trace_clock.c | 9 +++++---- 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b7566fe4d607..dcdf4e682dd4 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -764,7 +764,7 @@ static struct { { trace_clock_local, "local", 1 }, { trace_clock_global, "global", 1 }, { trace_clock_counter, "counter", 0 }, - { trace_clock_jiffies, "uptime", 1 }, + { trace_clock_jiffies, "uptime", 0 }, { trace_clock, "perf", 1 }, ARCH_TRACE_CLOCKS }; diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 26dc348332b7..57b67b1f24d1 100644 --- a/kernel/trace/trace_clock.c +++ b/kernel/trace/trace_clock.c @@ -59,13 +59,14 @@ u64 notrace trace_clock(void) /* * trace_jiffy_clock(): Simply use jiffies as a clock counter. + * Note that this use of jiffies_64 is not completely safe on + * 32-bit systems. But the window is tiny, and the effect if + * we are affected is that we will have an obviously bogus + * timestamp on a trace event - i.e. not life threatening. */ u64 notrace trace_clock_jiffies(void) { - u64 jiffy = jiffies - INITIAL_JIFFIES; - - /* Return nsecs */ - return (u64)jiffies_to_usecs(jiffy) * 1000ULL; + return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES); } /* -- 2.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/