[PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

[PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

[Rolf Eike Beer]

The documentation of msecs_to_jiffies() says:

 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 *
 * - 'too large' values [that would result in larger than
 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.

But when you pass in e.g. MAX_JIFFY_OFFSET + 1000 for HZ = 1000 it will not
return MAX_JIFFY_OFFSET, but the bigger value. This makes sure that the value
returned from this function can never be bigger than MAX_JIFFY_OFFSET. Also
use DIV_ROUND_UP() in one place where that is open coded.

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
---
 kernel/time.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/time.c b/kernel/time.c
index 8e8dc6d..1ccec53 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -433,6 +433,7 @@ EXPORT_SYMBOL(ns_to_timeval);
  */
 unsigned long msecs_to_jiffies(const unsigned int m)
 {
+	unsigned long r;
 	/*
 	 * Negative value, means infinite timeout:
 	 */
@@ -445,7 +446,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
 	 * round multiple of HZ, divide with the factor between them,
 	 * but round upwards:
 	 */
-	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
+	r = DIV_ROUND_UP(m, MSEC_PER_SEC / HZ);
 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
 	/*
 	 * HZ is larger than 1000, and HZ is a nice round multiple of
@@ -457,7 +458,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
 	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 		return MAX_JIFFY_OFFSET;
 
-	return m * (HZ / MSEC_PER_SEC);
+	r = m * (HZ / MSEC_PER_SEC);
 #else
 	/*
 	 * Generic case - multiply, round and divide. But first
@@ -467,9 +468,10 @@ unsigned long msecs_to_jiffies(const unsigned int m)
 	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
 		return MAX_JIFFY_OFFSET;
 
-	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
+	r = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 		>> MSEC_TO_HZ_SHR32;
 #endif
+	return min_t(unsigned long, r, MAX_JIFFY_OFFSET);
 }
 EXPORT_SYMBOL(msecs_to_jiffies);
 
-- 
1.7.3.2

Re: [PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

[Thomas Gleixner]

On Tue, 29 Mar 2011, Rolf Eike Beer wrote:

> The documentation of msecs_to_jiffies() says:
> 
>  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
>  *
>  * - 'too large' values [that would result in larger than
>  *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
> 
> But when you pass in e.g. MAX_JIFFY_OFFSET + 1000 for HZ = 1000 it will not
> return MAX_JIFFY_OFFSET, but the bigger value. This makes sure that the value

That's only true for 32 bit.

> returned from this function can never be bigger than MAX_JIFFY_OFFSET. Also
> use DIV_ROUND_UP() in one place where that is open coded.

>  unsigned long msecs_to_jiffies(const unsigned int m)
>  {
> +	unsigned long r;
>  	/*
>  	 * Negative value, means infinite timeout:
>  	 */
> @@ -445,7 +446,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
>  	 * round multiple of HZ, divide with the factor between them,
>  	 * but round upwards:
>  	 */
> -	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> +	r = DIV_ROUND_UP(m, MSEC_PER_SEC / HZ);
>  #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
>  	/*
>  	 * HZ is larger than 1000, and HZ is a nice round multiple of
> @@ -457,7 +458,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
>  	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
>  		return MAX_JIFFY_OFFSET;
>  
> -	return m * (HZ / MSEC_PER_SEC);
> +	r = m * (HZ / MSEC_PER_SEC);

For this case the jiffies_to_msec() check should be sufficient.

>  #else
>  	/*
>  	 * Generic case - multiply, round and divide. But first
> @@ -467,9 +468,10 @@ unsigned long msecs_to_jiffies(const unsigned int m)
>  	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
>  		return MAX_JIFFY_OFFSET;

Hmm, this check is silly. MUL32 is chosen, so that we cannot overflow.

> -	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> +	r = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
  		>> MSEC_TO_HZ_SHR32;

>  #endif
> +	return min_t(unsigned long, r, MAX_JIFFY_OFFSET);
>  }
>  EXPORT_SYMBOL(msecs_to_jiffies);

I start to wonder whether we really need these three variants or
whether we just could go with that MUL/SHIFT based implementation and
a final check for MAX_JIFFY_OFFSET. That would boil down to:

unsigned long msecs_to_jiffies(const unsigned int m)
{
	u64 res = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32) >> MSEC_TO_HZ_SHR32;

	return min_t(unsigned long, (unsigned long)res, MAX_JIFFY_OFFSET);
}

That'd avoid the whole division and msecs_to_jiffies() is not really a
high precision function.

Thanks,

	tglx

Re: [PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

[Rolf Eike Beer]

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Am Dienstag, 29. März 2011, 21:42:59 schrieb Thomas Gleixner:
> On Tue, 29 Mar 2011, Rolf Eike Beer wrote:

> > @@ -467,9 +468,10 @@ unsigned long msecs_to_jiffies(const unsigned int m)
> > 
> >  	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> >  	
> >  		return MAX_JIFFY_OFFSET;
> 
> Hmm, this check is silly. MUL32 is chosen, so that we cannot overflow.

IMHO the second part of the check should be enough, no? If m is greater than 
j2m(MAX) then it's irrelevant what's up else, it's too big. Period.

Eike

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Re: [PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

[Rolf Eike Beer]

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Am Dienstag, 29. März 2011, 21:42:59 schrieb Thomas Gleixner:
> On Tue, 29 Mar 2011, Rolf Eike Beer wrote:
> > The documentation of msecs_to_jiffies() says:
> >  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
> >  *
> >  * - 'too large' values [that would result in larger than
> >  *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
> > 
> > But when you pass in e.g. MAX_JIFFY_OFFSET + 1000 for HZ = 1000 it will
> > not return MAX_JIFFY_OFFSET, but the bigger value. This makes sure that
> > the value
> 
> That's only true for 32 bit.
> 
> > returned from this function can never be bigger than MAX_JIFFY_OFFSET.
> > Also use DIV_ROUND_UP() in one place where that is open coded.
> > 
> >  unsigned long msecs_to_jiffies(const unsigned int m)
> >  {
> > 
> > +	unsigned long r;
> > 
> >  	/*
> >  	
> >  	 * Negative value, means infinite timeout:
> >  	 */
> > 
> > @@ -445,7 +446,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
> > 
> >  	 * round multiple of HZ, divide with the factor between them,
> >  	 * but round upwards:
> >  	 */
> > 
> > -	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> > +	r = DIV_ROUND_UP(m, MSEC_PER_SEC / HZ);
> > 
> >  #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
> >  
> >  	/*
> >  	
> >  	 * HZ is larger than 1000, and HZ is a nice round multiple of
> > 
> > @@ -457,7 +458,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
> > 
> >  	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> >  	
> >  		return MAX_JIFFY_OFFSET;
> > 
> > -	return m * (HZ / MSEC_PER_SEC);
> > +	r = m * (HZ / MSEC_PER_SEC);
> 
> For this case the jiffies_to_msec() check should be sufficient.
> 
> >  #else
> >  
> >  	/*
> >  	
> >  	 * Generic case - multiply, round and divide. But first
> > 
> > @@ -467,9 +468,10 @@ unsigned long msecs_to_jiffies(const unsigned int
> > m)
> > 
> >  	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> >  	
> >  		return MAX_JIFFY_OFFSET;
> 
> Hmm, this check is silly. MUL32 is chosen, so that we cannot overflow.
> 
> > -	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> > +	r = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> > 
>   		>> MSEC_TO_HZ_SHR32;
> >  
> >  #endif
> > 
> > +	return min_t(unsigned long, r, MAX_JIFFY_OFFSET);
> > 
> >  }
> >  EXPORT_SYMBOL(msecs_to_jiffies);
> 
> I start to wonder whether we really need these three variants or
> whether we just could go with that MUL/SHIFT based implementation and
> a final check for MAX_JIFFY_OFFSET. That would boil down to:
> 
> unsigned long msecs_to_jiffies(const unsigned int m)
> {
> 	u64 res = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32) >> MSEC_TO_HZ_SHR32;
> 
> 	return min_t(unsigned long, (unsigned long)res, MAX_JIFFY_OFFSET);
> }
> 
> That'd avoid the whole division and msecs_to_jiffies() is not really a
> high precision function.

Ping? Is anyone going to either take my patch or do it's own reworking of that 
function?

Eike

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