From: Dave Hansen <dave.han...@linux.intel.com>
This fixes a bug present in 3.10 and introduced here:
commit 2ab00456ea8a0d79acb1390659b98416111880b2
Author: Dave Hansen <dave.han...@linux.intel.com>
Date: Fri Jun 21 08:51:35 2013 -0700
x86: Warn when NMI handlers take large amounts of time
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
Both of these fixes need to get pulled in to Linus's tree and
the 3.10 stable tree.
Signed-off-by: Dave Hansen <dave.han...@linux.intel.com>
Cc: sta...@vger.kernel.org
Cc: x...@kernel.org
---
linux.git-davehans/arch/x86/kernel/nmi.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff -puN arch/x86/kernel/nmi.c~dave-is-stupid-do_div arch/x86/kernel/nmi.c
--- linux.git/arch/x86/kernel/nmi.c~dave-is-stupid-do_div 2013-07-08
13:10:55.498656504 -0700
+++ linux.git-davehans/arch/x86/kernel/nmi.c 2013-07-08 13:10:55.501656637
-0700
@@ -111,7 +111,7 @@ static int __kprobes nmi_handle(unsigned
*/
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
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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