CC alpha, mips On Fri, Jun 22, 2018 at 9:54 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > For the common cases where 1000 is a multiple of HZ, or HZ is a multiple > of 1000, jiffies_to_msecs() never returns zero when passed a non-zero > time period. > > However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 1024 or > 1200, as used on alpha and DECstation), jiffies_to_msecs() may return > zero for small non-zero time periods. This may break code that relies > on receiving back a non-zero value. > > jiffies_to_usecs() does not need such a fix, as <linux/jiffies.h> does > not support values of HZ larger than 12287, thus rejecting any > problematic huge values of HZ. > > Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> > --- > v2: > - Add examples of affected systems, > - Use DIV_ROUND_UP(). > --- > kernel/time/time.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/time/time.c b/kernel/time/time.c > index 6fa99213fc720e4b..2b41e8e2d31db26f 100644 > --- a/kernel/time/time.c > +++ b/kernel/time/time.c > @@ -28,6 +28,7 @@ > */ > > #include <linux/export.h> > +#include <linux/kernel.h> > #include <linux/timex.h> > #include <linux/capability.h> > #include <linux/timekeeper_internal.h> > @@ -314,9 +315,10 @@ unsigned int jiffies_to_msecs(const unsigned long j) > return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC); > #else > # if BITS_PER_LONG == 32 > - return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32; > + return (HZ_TO_MSEC_MUL32 * j + (1ULL << HZ_TO_MSEC_SHR32) - 1) >> > + HZ_TO_MSEC_SHR32; > # else > - return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN; > + return DIV_ROUND_UP(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN); > # endif > #endif > } > -- > 2.17.1
