* [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
@ 2018-06-22 7:54 Geert Uytterhoeven
2018-06-22 8:11 ` Geert Uytterhoeven
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Geert Uytterhoeven @ 2018-06-22 7:54 UTC (permalink / raw)
To: John Stultz, Thomas Gleixner, Stephen Boyd, Arnd Bergmann
Cc: linux-kernel, Geert Uytterhoeven
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, as <linux/jiffies.h> does
not support values of HZ larger than 12287, thus rejecting any
problematic huge values of HZ.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
v2:
- Add examples of affected systems,
- Use DIV_ROUND_UP().
---
kernel/time/time.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 6fa99213fc720e4b..2b41e8e2d31db26f 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
}
--
2.17.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
2018-06-22 7:54 [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods Geert Uytterhoeven
@ 2018-06-22 8:11 ` Geert Uytterhoeven
2018-06-22 8:19 ` Arnd Bergmann
2018-06-22 12:49 ` Thomas Gleixner
2 siblings, 0 replies; 6+ messages in thread
From: Geert Uytterhoeven @ 2018-06-22 8:11 UTC (permalink / raw)
To: John Stultz, Thomas Gleixner, Stephen Boyd, Arnd Bergmann
Cc: Linux Kernel Mailing List, alpha, Linux MIPS Mailing List
CC alpha, mips
On Fri, Jun 22, 2018 at 9:54 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> 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, as <linux/jiffies.h> does
> not support values of HZ larger than 12287, thus rejecting any
> problematic huge values of HZ.
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> v2:
> - Add examples of affected systems,
> - Use DIV_ROUND_UP().
> ---
> kernel/time/time.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/time/time.c b/kernel/time/time.c
> index 6fa99213fc720e4b..2b41e8e2d31db26f 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
> }
> --
> 2.17.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
2018-06-22 7:54 [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods Geert Uytterhoeven
2018-06-22 8:11 ` Geert Uytterhoeven
@ 2018-06-22 8:19 ` Arnd Bergmann
2018-06-22 12:49 ` Thomas Gleixner
2 siblings, 0 replies; 6+ messages in thread
From: Arnd Bergmann @ 2018-06-22 8:19 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: John Stultz, Thomas Gleixner, Stephen Boyd, Linux Kernel Mailing List
On Fri, Jun 22, 2018 at 9:54 AM, Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
> 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, as <linux/jiffies.h> does
> not support values of HZ larger than 12287, thus rejecting any
> problematic huge values of HZ.
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
Looks good to me,
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
2018-06-22 7:54 [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods Geert Uytterhoeven
2018-06-22 8:11 ` Geert Uytterhoeven
2018-06-22 8:19 ` Arnd Bergmann
@ 2018-06-22 12:49 ` Thomas Gleixner
2018-06-22 13:09 ` Geert Uytterhoeven
2 siblings, 1 reply; 6+ messages in thread
From: Thomas Gleixner @ 2018-06-22 12:49 UTC (permalink / raw)
To: Geert Uytterhoeven; +Cc: John Stultz, Stephen Boyd, Arnd Bergmann, linux-kernel
On Fri, 22 Jun 2018, Geert Uytterhoeven wrote:
> 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, as <linux/jiffies.h> does
> not support values of HZ larger than 12287, thus rejecting any
> problematic huge values of HZ.
Sorry, I'm not understanding that sentence at all.
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
This lacks a stable tag, right?
> ---
> v2:
> - Add examples of affected systems,
> - Use DIV_ROUND_UP().
> ---
> kernel/time/time.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/time/time.c b/kernel/time/time.c
> index 6fa99213fc720e4b..2b41e8e2d31db26f 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
> }
> --
> 2.17.1
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
2018-06-22 12:49 ` Thomas Gleixner
@ 2018-06-22 13:09 ` Geert Uytterhoeven
2018-06-22 13:42 ` Thomas Gleixner
0 siblings, 1 reply; 6+ messages in thread
From: Geert Uytterhoeven @ 2018-06-22 13:09 UTC (permalink / raw)
To: Thomas Gleixner
Cc: John Stultz, Stephen Boyd, Arnd Bergmann,
Linux Kernel Mailing List, alpha, Linux MIPS Mailing List
Hi Thomas,
On Fri, Jun 22, 2018 at 2:49 PM Thomas Gleixner <tglx@linutronix.de> wrote:
> On Fri, 22 Jun 2018, Geert Uytterhoeven wrote:
> > 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, as <linux/jiffies.h> does
> > not support values of HZ larger than 12287, thus rejecting any
> > problematic huge values of HZ.
>
> Sorry, I'm not understanding that sentence at all.
Sorry for being unclear.
1 jiffy can only be less than 1µs if HZ > 1000000.
But include/linux/jiffies.h checks if HZ >= 12288, and does #error otherwise.
In addition, there's a "BUILD_BUG_ON(HZ > USEC_PER_SEC)" in time.c
> > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> This lacks a stable tag, right?
Up to the maintainer to add, isn't it?
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods
2018-06-22 13:09 ` Geert Uytterhoeven
@ 2018-06-22 13:42 ` Thomas Gleixner
0 siblings, 0 replies; 6+ messages in thread
From: Thomas Gleixner @ 2018-06-22 13:42 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: John Stultz, Stephen Boyd, Arnd Bergmann,
Linux Kernel Mailing List, alpha, Linux MIPS Mailing List
[-- Attachment #1: Type: text/plain, Size: 1418 bytes --]
On Fri, 22 Jun 2018, Geert Uytterhoeven wrote:
> On Fri, Jun 22, 2018 at 2:49 PM Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Fri, 22 Jun 2018, Geert Uytterhoeven wrote:
> > > 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, as <linux/jiffies.h> does
> > > not support values of HZ larger than 12287, thus rejecting any
> > > problematic huge values of HZ.
> >
> > Sorry, I'm not understanding that sentence at all.
>
> Sorry for being unclear.
>
> 1 jiffy can only be less than 1µs if HZ > 1000000.
> But include/linux/jiffies.h checks if HZ >= 12288, and does #error otherwise.
> In addition, there's a "BUILD_BUG_ON(HZ > USEC_PER_SEC)" in time.c
Hmm, ok. Care to reword?
> > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> >
> > This lacks a stable tag, right?
>
> Up to the maintainer to add, isn't it?
Yes and no. At least a hint that this has been broken by commit X or has
been broken forever would be appreciated.
Thanks,
tglx
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-06-22 13:42 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-06-22 7:54 [PATCH v2] time: Make sure jiffies_to_msecs() preserves non-zero time periods Geert Uytterhoeven
2018-06-22 8:11 ` Geert Uytterhoeven
2018-06-22 8:19 ` Arnd Bergmann
2018-06-22 12:49 ` Thomas Gleixner
2018-06-22 13:09 ` Geert Uytterhoeven
2018-06-22 13:42 ` Thomas Gleixner
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).