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| author |   Salman Qazi <sqazi@google.com> | 2012-03-09 16:41:01 -0800 |
|---|---|---|
| committer |   Ingo Molnar <mingo@elte.hu> | 2012-03-13 16:27:51 +0100 |
| commit | 9993bc635d01a6ee7f6b833b4ee65ce7c06350b1 (patch) | |
| tree | 9e40c69ef513fc0a57c03a05a68afc6711418ed8 /include | |
| parent | Merge tag 'v3.3-rc7' into sched/core (diff) | |
| download | linux-dev-9993bc635d01a6ee7f6b833b4ee65ce7c06350b1.tar.xz linux-dev-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 'include')
| -rw-r--r-- | include/linux/kernel.h | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index e8343422240a..d801acb5e680 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -85,6 +85,19 @@ } \ ) +/* + * Multiplies an integer by a fraction, while avoiding unnecessary + * overflow or loss of precision. + */ +#define mult_frac(x, numer, denom)( \ +{ \ + typeof(x) quot = (x) / (denom); \ + typeof(x) rem = (x) % (denom); \ + (quot * (numer)) + ((rem * (numer)) / (denom)); \ +} \ +) + + #define _RET_IP_ (unsigned long)__builtin_return_address(0) #define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; }) |