lkml.org 
[lkml]   [2012]   [Mar]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectWrong use of MAX_JIFFY_OFFSET?
Date
Hi guys,

I saw a couple of places in current kernel have this kind of code:

> static inline unsigned int elapsed_jiffies_msecs(unsigned long start)
> {
> unsigned long end = jiffies;
>
> if (end >= start)
> return jiffies_to_msecs(end - start);
>
> return jiffies_to_msecs(end + (MAX_JIFFY_OFFSET - start) + 1);
> }

As you know, jiffies has a type of unsigned long, so if we know which is the
end and
which is the start, then (end - start) can simply figure out how much
jiffies flies,
without worry about the overflow.

Look at the code above, assume that there is just an overflow happening on
jiffies: end=0 and start=~0UL.
Since end < start, then the return value of the function is
jiffies_to_msecs(MAX_JIFFY_OFFSET+2).
But shouldn't the correct value be jiffies_to_msecs(1)?

could someone tell me that am I missing anything?

Thanks,
Yu



\
 
 \ /
  Last update: 2012-03-28 09:15    [W:0.098 / U:0.752 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site