| From: Geert Uytterhoeven <geert@linux-m68k.org> |
| Date: Fri, 22 Jun 2018 16:33:57 +0200 |
| Subject: time: Make sure jiffies_to_msecs() preserves non-zero time periods |
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| |
| commit abcbcb80cd09cd40f2089d912764e315459b71f7 upstream. |
| |
| 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: one jiffy can only be less |
| than one ยตs if HZ > 1000000, and such large values of HZ are already |
| rejected at build time, twice: |
| |
| - include/linux/jiffies.h does #error if HZ >= 12288, |
| - kernel/time/time.c has BUILD_BUG_ON(HZ > USEC_PER_SEC). |
| |
| Broken since forever. |
| |
| Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Reviewed-by: Arnd Bergmann <arnd@arndb.de> |
| Cc: John Stultz <john.stultz@linaro.org> |
| Cc: Stephen Boyd <sboyd@kernel.org> |
| Cc: linux-alpha@vger.kernel.org |
| Cc: linux-mips@linux-mips.org |
| Link: https://lkml.kernel.org/r/20180622143357.7495-1-geert@linux-m68k.org |
| [bwh: Backported to 3.16: adjust filename] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| kernel/time.c | 6 ++++-- |
| 1 file changed, 4 insertions(+), 2 deletions(-) |
| |
| --- a/kernel/time.c |
| +++ b/kernel/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> |
| @@ -253,9 +254,10 @@ unsigned int jiffies_to_msecs(const unsi |
| 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 |
| } |
