linux-kernel - [60/90] [S390] fix cputime overflow in uptime_proc

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Date:	Mon, 23 Jan 2012 15:39:46 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	Michael Abbott <michael.abbott@...mond.ac.uk>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: [60/90] [S390] fix cputime overflow in uptime_proc_show

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@...ibm.com>

commit c3e0ef9a298e028a82ada28101ccd5cf64d209ee upstream.

For 32-bit architectures using standard jiffies the idletime calculation
in uptime_proc_show will quickly overflow. It takes (2^32 / HZ) seconds
of idle-time, or e.g. 12.45 days with no load on a quad-core with HZ=1000.
Switch to 64-bit calculations.

Cc: Michael Abbott <michael.abbott@...mond.ac.uk>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/proc/uptime.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/fs/proc/uptime.c
+++ b/fs/proc/uptime.c
@@ -11,15 +11,20 @@ static int uptime_proc_show(struct seq_f
 {
 	struct timespec uptime;
 	struct timespec idle;
+	cputime64_t idletime;
+	u64 nsec;
+	u32 rem;
 	int i;
-	cputime_t idletime = cputime_zero;
 
+	idletime = 0;
 	for_each_possible_cpu(i)
 		idletime = cputime64_add(idletime, kstat_cpu(i).cpustat.idle);
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	monotonic_to_bootbased(&uptime);
-	cputime_to_timespec(idletime, &idle);
+	nsec = cputime64_to_jiffies64(idletime) * TICK_NSEC;
+	idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
+	idle.tv_nsec = rem;
 	seq_printf(m, "%lu.%02lu %lu.%02lu\n",
 			(unsigned long) uptime.tv_sec,
 			(uptime.tv_nsec / (NSEC_PER_SEC / 100)),


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