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Commit 41cf5445 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
Browse files

[PATCH] Fix multiple conversion bugs in msecs_to_jiffies 



Fix multiple conversion bugs in msecs_to_jiffies().

The main problem is that this condition:

	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))

overflows if HZ is smaller than 1000!

This change is user-visible: for HZ=250 SUS-compliant poll()-timeout
value of -20 is mistakenly converted to 'immediate timeout'.

(The new dyntick code also triggered this, that's how we noticed.)

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8b9365d7

kernel/time.c

+42 −1
Original line number Diff line number Diff line
@@ -500,15 +500,56 @@ unsigned int jiffies_to_usecs(const unsigned long j) 
}

EXPORT_SYMBOL(jiffies_to_usecs);



/*

 * When we convert to jiffies then we interpret incoming values

 * the following way:

 *

 * - 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.

 *

 * - all other values are converted to jiffies by either multiplying

 *   the input value by a factor or dividing it with a factor

 *

 * We must also be careful about 32-bit overflows.

 */

unsigned long msecs_to_jiffies(const unsigned int m)

{

	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))

	/*

	 * Negative value, means infinite timeout:

	 */

	if ((int)m < 0)

		return MAX_JIFFY_OFFSET;



#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)

	/*

	 * HZ is equal to or smaller than 1000, and 1000 is a nice

	 * round multiple of HZ, divide with the factor between them,

	 * but round upwards:

	 */

	return (m + (MSEC_PER_SEC / HZ) - 1) / (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

	 * 1000 - simply multiply with the factor between them.

	 *

	 * But first make sure the multiplication result cannot

	 * overflow:

	 */

	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))

		return MAX_JIFFY_OFFSET;



	return m * (HZ / MSEC_PER_SEC);

#else

	/*

	 * Generic case - multiply, round and divide. But first

	 * check that if we are doing a net multiplication, that

	 * we wouldnt overflow:

	 */

	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))

		return MAX_JIFFY_OFFSET;



	return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;

#endif

}