linux-kernel - [PATCH] fix msecs_to_jiffies() to not return values greater than MAX_JIFFY

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Message-Id: <2120287.WTetKHanc4@donald.sf-tec.de>
Date:	Tue, 29 Mar 2011 18:38:46 +0200
From:	Rolf Eike Beer <eike-kernel@...tec.de>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] 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.

Signed-off-by: Rolf Eike Beer <eike-kernel@...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


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