(crap crap crap... M.A.I.N.T.A.I.N.E.R.S _dummy_) clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns()
As per 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock", cycles * mult >> shift is overflow prone. so give it the same treatment. Cc: Salman Qazi <[email protected]> Cc: John Stultz <[email protected]>, Signed-off-by: Mike Galbraith <[email protected]> --- include/linux/clocksource.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -77,13 +77,18 @@ struct timecounter { * * XXX - This could use some mult_lxl_ll() asm optimization. Same code * as in cyc2ns, but with unsigned result. + * + * Because it is the same as x86 __cycles_2_ns, give it the same treatment as + * commit 4cecf6d401a "sched, x86: Avoid unnecessary overflow in sched_clock" + * to avoid a potential cycles * mult overflow. */ static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc, cycle_t cycles) { - u64 ret = (u64)cycles; - ret = (ret * cc->mult) >> cc->shift; - return ret; + u64 quot = (u64)cycles >> cc->shift; + u64 rem = (u64)cycles & ((1ULL << cc->shift) - 1); + + return quot * cc->mult + ((rem * cc->mult) >> cc->shift); } /** -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
