From: Dave Hansen Date: Mon, 8 Jul 2013 21:44:04 +0000 (-0700) Subject: perf/x86: Fix incorrect use of do_div() in NMI warning X-Git-Tag: v3.11-rc1~10^2 X-Git-Url: http://git.cascardo.info/?p=cascardo%2Flinux.git;a=commitdiff_plain;h=baf64b85445546a38b44052d71782dfe7531e350 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 Cc: Dave Hansen Link: http://lkml.kernel.org/r/20130708214404.B0B6EA66@viggo.jf.intel.com Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 0920212e6159..ba77ebc2c353 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,