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author | Salman Qazi <sqazi@google.com> | 2012-03-09 16:41:01 -0800 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-04-13 08:14:08 -0700 |
commit | ee9c2e08d37dae695a4f4cfb4dc003c5c2576f79 (patch) | |
tree | 82c0d322544c9a6ef56c1100a07a80e5d48b6f17 /arch/x86/include | |
parent | 1802657ecb10d7ca620c3cf642920009d1aa2ec3 (diff) | |
download | kernel_samsung_tuna-ee9c2e08d37dae695a4f4cfb4dc003c5c2576f79.zip kernel_samsung_tuna-ee9c2e08d37dae695a4f4cfb4dc003c5c2576f79.tar.gz kernel_samsung_tuna-ee9c2e08d37dae695a4f4cfb4dc003c5c2576f79.tar.bz2 |
sched/x86: Fix overflow in cyc2ns_offset
commit 9993bc635d01a6ee7f6b833b4ee65ce7c06350b1 upstream.
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>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86/include')
-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 431793e..34baa0e 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; } |