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time: Make sure jiffies_to_msecs() preserves non-zero time periods

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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
This commit is contained in:
Geert Uytterhoeven 2018-06-22 16:33:57 +02:00 committed by Thomas Gleixner
parent 0fe2795516
commit abcbcb80cd
1 changed files with 4 additions and 2 deletions
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6
kernel/time/time.c
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@ -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
}