diff options
| author | Salman Qazi <sqazi@google.com> | 2012-03-09 16:41:01 -0800 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2012-10-07 23:37:38 +0200 |
| commit | ab81b6abd9a1cdac0d6e84515cc808f735fc78b7 (patch) | |
| tree | 694b87cdf2d0f88942a9eda5ad24c4b5866963a5 /include | |
| parent | 0d1e8b8281ae7b43be54ec3409d299c99d7c975d (diff) | |
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>
Signed-off-by: Willy Tarreau <w@1wt.eu>
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 9acb92d8fb06..3526cd4a0066 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -55,6 +55,19 @@ extern const char linux_proc_banner[]; } \ ) +/* + * 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; }) |