From owner-freebsd-bugs  Wed May  9  6:31:47 2001
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Date: Wed, 9 May 2001 23:30:09 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: dwmalone@FreeBSD.ORG
Cc: freebsd-bugs@FreeBSD.ORG, des@FreeBSD.ORG
Subject: Re: kern/27215: when cat'ing /compat/linux/proc/stat, we have negative
 numbers
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On Wed, 9 May 2001 dwmalone@FreeBSD.ORG wrote:

> Synopsis: when cat'ing /compat/linux/proc/stat, we have negative numbers
> 
> Responsible-Changed-From-To: freebsd-bugs->des
> Responsible-Changed-By: dwmalone
> Responsible-Changed-When: Wed May 9 03:16:06 PDT 2001
> Responsible-Changed-Why: 
> Linprocfs is DES's. The patch looks straightforward though.

It mainly obscures the bug, by moving obvious overflow after LONG_MAX/100
statclock ticks to unobvious overflow after ULONG_MAX/100 statclock ticks.
Overflow thresholds for some cases:

i386, stathz = 128: before: 1.94 days; after : 3.88 days
alpha, stathz = 1024: before: 2.85 million years; after: 5.71 million years

BTW, cp_time[x] has a stupid type.  We use uint64_t to count ticks
for individual processes (p_[uis]ticks in struct proc) but we still
use "long" for cp_time[x].  Thus the tick counters for system times
may overflow after 194 days on i386's with the default stathz, but
the tick counters for individual processes don't overflow for 571
million years on the same system.  However, calcru() doesn't actually
work for 64-bit tick counters, so getrusage(2) breaks down for processes
that have run for more than about 388 days.  This overflow has actually
been reported.  See PR17482.

Bruce


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