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| author | Geert Uytterhoeven <geert@linux-m68k.org> | 2018-06-22 16:33:57 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-06-22 17:48:36 +0200 |
| commit | abcbcb80cd09cd40f2089d912764e315459b71f7 (patch) | |
| tree | 59af967e2f23d75658297fd701b39ea468c77a51 /kernel/time | |
| parent | 0fe2795516b9e1c59b58b02bdf8658698117ec4e (diff) | |
| download | linux-abcbcb80cd09cd40f2089d912764e315459b71f7.tar.bz2 | |
time: Make sure jiffies_to_msecs() preserves non-zero time periods
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 µs 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
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180622143357.7495-1-geert@linux-m68k.org
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/time.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/time/time.c b/kernel/time/time.c index 6fa99213fc72..2b41e8e2d31d 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 } |