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authorIngo Molnar <mingo@elte.hu>2007-02-16 01:27:28 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-02-16 08:13:56 -0800
commit41cf54455da5e5dc847a9733d49ca23b5e7dd59e (patch)
treeea7aa5fe473f4716e4190f7a90a7663535fee312 /kernel/time.c
parent8b9365d753d9870bb6451504c13570b81923228f (diff)
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[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: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: john stultz <johnstul@us.ibm.com> Cc: Roman Zippel <zippel@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/time.c')
-rw-r--r--kernel/time.c43
1 files changed, 42 insertions, 1 deletions
diff --git a/kernel/time.c b/kernel/time.c
index 4a8657171584..c6c80ea5d0ea 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -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
}