linux-kernel - [tip:perf/urgent] perf/x86: Fix incorrect use of do

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Message-ID: <tip-baf64b85445546a38b44052d71782dfe7531e350@git.kernel.org>
Date:	Fri, 12 Jul 2013 06:30:00 -0700
From:	tip-bot for Dave Hansen <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	dave.hansen@...ux.intel.com, tglx@...utronix.de, dave@...1.net
Subject: [tip:perf/urgent] perf/x86: Fix incorrect use of do_div()
  in NMI warning

Commit-ID:  baf64b85445546a38b44052d71782dfe7531e350
Gitweb:     http://git.kernel.org/tip/baf64b85445546a38b44052d71782dfe7531e350
Author:     Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate: Mon, 8 Jul 2013 14:44:04 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 12 Jul 2013 14:13:04 +0200

perf/x86: Fix incorrect use of do_div() in NMI warning

I completely botched understanding the calling conventions of
do_div().  I assumed that do_div() returned the result instead
of realizing that it modifies its argument and returns a
remainder.  The side-effect from this would be bogus numbers
for the "msecs" value in the warning messages:

	INFO: NMI handler (perf_event_nmi_handler) took too long to run: 0.114 msecs

Note, there was a second fix posted by Stephane Eranian for
a separate patch which I also botched:

	http://lkml.kernel.org/r/20130704223010.GA30625@quad

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dave Hansen <dave@...1.net>
Link: http://lkml.kernel.org/r/20130708214404.B0B6EA66@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/nmi.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 0920212..ba77ebc 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -111,7 +111,7 @@ static int __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2
 	 */
 	list_for_each_entry_rcu(a, &desc->head, list) {
 		u64 before, delta, whole_msecs;
-		int decimal_msecs, thishandled;
+		int remainder_ns, decimal_msecs, thishandled;
 
 		before = local_clock();
 		thishandled = a->handler(type, regs);
@@ -123,8 +123,9 @@ static int __kprobes nmi_handle(unsigned int type, struct pt_regs *regs, bool b2
 			continue;
 
 		nmi_longest_ns = delta;
-		whole_msecs = do_div(delta, (1000 * 1000));
-		decimal_msecs = do_div(delta, 1000) % 1000;
+		whole_msecs = delta;
+		remainder_ns = do_div(whole_msecs, (1000 * 1000));
+		decimal_msecs = remainder_ns / 1000;
 		printk_ratelimited(KERN_INFO
 			"INFO: NMI handler (%ps) took too long to run: "
 			"%lld.%03d msecs\n", a->handler, whole_msecs,
--
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