fix msecs_to_jiffies() to not return values greater than MAX_JIFFY_OFFSET

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.

unsigned long msecs_to_jiffies(const unsigned int m) {

kernel/time.c +2 -1

+	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

kernel/time.c unsigned long msecs_to_jiffies(const unsigned int m) · line 471

Quoted 6 lines

kernel/time.c +0 -0

@@ -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.

Quoted 9 lines

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.

Quoted 29 lines

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) {

kernel/time.c +2 -1

+	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)

kernel/time.c +0 -0

 	/*
 
 	 * HZ is larger than 1000, and HZ is a nice round multiple of

kernel/time.c unsigned long msecs_to_jiffies(const unsigned int m) · line 463

Quoted 7 lines

kernel/time.c +1 -1

@@ -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.

kernel/time.c unsigned long msecs_to_jiffies(const unsigned int · line 472

Quoted 12 lines

(quoted diff) +0 -0

 #else

kernel/time.c +0 -0

 	/*
 
 	 * 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.

kernel/time.c unsigned long msecs_to_jiffies(const unsigned int m) · line 477

Quoted 3 lines

kernel/time.c +1 -1

-	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
+	r = (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
 

>> MSEC_TO_HZ_SHR32;

Quoted 7 lines

kernel/time.c +1 -0

 #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.