releases/4.14.53/time-make-sure-jiffies_to_msecs-preserves-non-zero-time-periods.patch

   1 From abcbcb80cd09cd40f2089d912764e315459b71f7 Mon Sep 17 00:00:00 2001
   2 From: Geert Uytterhoeven <geert@linux-m68k.org>
   3 Date: Fri, 22 Jun 2018 16:33:57 +0200
   4 Subject: time: Make sure jiffies_to_msecs() preserves non-zero time periods
   5 MIME-Version: 1.0
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   8
   9 From: Geert Uytterhoeven <geert@linux-m68k.org>
  10
  11 commit abcbcb80cd09cd40f2089d912764e315459b71f7 upstream.
  12
  13 For the common cases where 1000 is a multiple of HZ, or HZ is a multiple of
  14 1000, jiffies_to_msecs() never returns zero when passed a non-zero time
  15 period.
  16
  17 However, if HZ > 1000 and not an integer multiple of 1000 (e.g. 1024 or
  18 1200, as used on alpha and DECstation), jiffies_to_msecs() may return zero
  19 for small non-zero time periods.  This may break code that relies on
  20 receiving back a non-zero value.
  21
  22 jiffies_to_usecs() does not need such a fix: one jiffy can only be less
  23 than one µs if HZ > 1000000, and such large values of HZ are already
  24 rejected at build time, twice:
  25
  26   - include/linux/jiffies.h does #error if HZ >= 12288,
  27   - kernel/time/time.c has BUILD_BUG_ON(HZ > USEC_PER_SEC).
  28
  29 Broken since forever.
  30
  31 Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
  32 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  33 Reviewed-by: Arnd Bergmann <arnd@arndb.de>
  34 Cc: John Stultz <john.stultz@linaro.org>
  35 Cc: Stephen Boyd <sboyd@kernel.org>
  36 Cc: linux-alpha@vger.kernel.org
  37 Cc: linux-mips@linux-mips.org
  38 Cc: stable@vger.kernel.org
  39 Link: https://lkml.kernel.org/r/20180622143357.7495-1-geert@linux-m68k.org
  40 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  41
  42 ---
  43  kernel/time/time.c |    6 ++++--
  44  1 file changed, 4 insertions(+), 2 deletions(-)
  45
  46 --- a/kernel/time/time.c
  47 +++ b/kernel/time/time.c
  48 @@ -28,6 +28,7 @@
  49   */
  50
  51  #include <linux/export.h>
  52 +#include <linux/kernel.h>
  53  #include <linux/timex.h>
  54  #include <linux/capability.h>
  55  #include <linux/timekeeper_internal.h>
  56 @@ -348,9 +349,10 @@ unsigned int jiffies_to_msecs(const unsi
  57         return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
  58  #else
  59  # if BITS_PER_LONG == 32
  60 -       return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
  61 +       return (HZ_TO_MSEC_MUL32 * j + (1ULL << HZ_TO_MSEC_SHR32) - 1) >>
  62 +              HZ_TO_MSEC_SHR32;
  63  # else
  64 -       return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
  65 +       return DIV_ROUND_UP(j * HZ_TO_MSEC_NUM, HZ_TO_MSEC_DEN);
  66  # endif
  67  #endif
  68  }