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authorGeert Uytterhoeven <geert@linux-m68k.org>2018-06-22 16:33:57 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-07-03 11:21:30 +0200
commit64a7976b4f3e6c5d1f7ec069807575ce447198c0 (patch)
treeca332c716d4c4bd0e55a5879b39dedab00ee9deb /kernel
parent3f74d64b44befdf44807e8e762b8010b772f0501 (diff)
time: Make sure jiffies_to_msecs() preserves non-zero time periods
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 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/time.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 86751c68e08d..de70ac1f84d0 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>
@@ -258,9 +259,10 @@ 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
}