Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422829AbaGRSn0 (ORCPT ); Fri, 18 Jul 2014 14:43:26 -0400 Received: from mga02.intel.com ([134.134.136.20]:62471 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030567AbaGRSnZ (ORCPT ); Fri, 18 Jul 2014 14:43:25 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,686,1400050800"; d="scan'208";a="575324214" Message-Id: <99d63c5bfe9b320a3b428d773825a37095bf6a51.1405708254.git.tony.luck@intel.com> In-Reply-To: <20140718133609.3125e72d@gandalf.local.home> From: Tony Luck Subject: [PATCH] tracing: Fix wraparound problems in "uptime" tracer To: Steven Rostedt Cc: Linux Kernel Mailing List , Ingo Molnar , , , "Xie XiuQi" Date: Fri, 18 Jul 2014 11:43:01 -0700 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The "uptime" tracer 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). Signed-off-by: Tony Luck --- 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 384ede311717..eb7d56480545 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -809,7 +809,7 @@ 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); } /* -- 1.8.4.1 -- 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/