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author | Salman Qazi <sqazi@google.com> | 2012-03-09 16:41:01 -0800 |
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committer | Ingo Molnar <mingo@elte.hu> | 2012-03-13 16:27:51 +0100 |
commit | 9993bc635d01a6ee7f6b833b4ee65ce7c06350b1 (patch) | |
tree | 9e40c69ef513fc0a57c03a05a68afc6711418ed8 /arch/x86/include/asm/timer.h | |
parent | 47258cf3c4aa5d56e678bafe0dd0d03ddd980b88 (diff) | |
download | linux-9993bc635d01a6ee7f6b833b4ee65ce7c06350b1.tar.gz linux-9993bc635d01a6ee7f6b833b4ee65ce7c06350b1.tar.bz2 linux-9993bc635d01a6ee7f6b833b4ee65ce7c06350b1.zip |
sched/x86: Fix overflow in cyc2ns_offset
When a machine boots up, the TSC generally gets reset. However,
when kexec is used to boot into a kernel, the TSC value would be
carried over from the previous kernel. The computation of
cycns_offset in set_cyc2ns_scale is prone to an overflow, if the
machine has been up more than 208 days prior to the kexec. The
overflow happens when we multiply *scale, even though there is
enough room to store the final answer.
We fix this issue by decomposing tsc_now into the quotient and
remainder of division by CYC2NS_SCALE_FACTOR and then performing
the multiplication separately on the two components.
Refactor code to share the calculation with the previous
fix in __cycles_2_ns().
Signed-off-by: Salman Qazi <sqazi@google.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Turner <pjt@google.com>
Cc: john stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20120310004027.19291.88460.stgit@dungbeetle.mtv.corp.google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/include/asm/timer.h')
-rw-r--r-- | arch/x86/include/asm/timer.h | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h index 431793e5d484..34baa0eb5d0c 100644 --- a/arch/x86/include/asm/timer.h +++ b/arch/x86/include/asm/timer.h @@ -57,14 +57,10 @@ DECLARE_PER_CPU(unsigned long long, cyc2ns_offset); static inline unsigned long long __cycles_2_ns(unsigned long long cyc) { - unsigned long long quot; - unsigned long long rem; int cpu = smp_processor_id(); unsigned long long ns = per_cpu(cyc2ns_offset, cpu); - quot = (cyc >> CYC2NS_SCALE_FACTOR); - rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1); - ns += quot * per_cpu(cyc2ns, cpu) + - ((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR); + ns += mult_frac(cyc, per_cpu(cyc2ns, cpu), + (1UL << CYC2NS_SCALE_FACTOR)); return ns; } |