Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=41cf54455da5e5dc847a9733d49ca23b5e7dd59e
Commit:     41cf54455da5e5dc847a9733d49ca23b5e7dd59e
Parent:     8b9365d753d9870bb6451504c13570b81923228f
Author:     Ingo Molnar <[EMAIL PROTECTED]>
AuthorDate: Fri Feb 16 01:27:28 2007 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Feb 16 08:13:56 2007 -0800

    [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 <[EMAIL PROTECTED]>
    Signed-off-by: Thomas Gleixner <[EMAIL PROTECTED]>
    Cc: john stultz <[EMAIL PROTECTED]>
    Cc: Roman Zippel <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 kernel/time.c |   43 ++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 42 insertions(+), 1 deletions(-)

diff --git a/kernel/time.c b/kernel/time.c
index 4a86571..c6c80ea 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
 }
-
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