[PATCH] fix oops in updating thread cputime and task time

[Fawzi Mohamed]

use div64_u64 instead of do_div to divide cputime_t with each other
because if cputime_t is u64 it does crash when overflowing u32.

    KERNEL: ./vmlinux-2.6.32.54-0.3-default.gz
 DEBUGINFO: .//vmlinux-2.6.32.54-0.3-default.debug
  DUMPFILE: ./vmcore
      CPUS: 24
      DATE: Mon Mar  5 00:58:10 2012
    UPTIME: 19 days, 11:01:56
LOAD AVERAGE: 0.74, 0.42, 0.40
     TASKS: 731
  NODENAME: node65
   RELEASE: 2.6.32.54-0.3-default
   VERSION: #1 SMP 2012-01-27 17:38:56 +0100
   MACHINE: x86_64  (3067 Mhz)
    MEMORY: 96 GB
     PANIC: ""
       PID: 11234
   COMMAND: "ricc2_smp"
      TASK: ffff881813de2240  [THREAD_INFO: ffff8818153c2000]
       CPU: 8
     STATE: TASK_RUNNING (PANIC)

crash> bt
PID: 11234  TASK: ffff881813de2240  CPU: 8   COMMAND: "ricc2_smp"
  RIP: 00007f5e4f418617  RSP: 00007f5e4dd3ebd0  RFLAGS: 00000202
  RAX: 0000000000000062  RBX: ffffffff81002f7b  RCX: 0000000000000179
  RDX: 00007f5e4dd3edb4  RSI: 00007f5e4dd3ec70  RDI: 0000000000000000
  RBP: 00007f5e4dd3ecf0   R8: 0000000000000001   R9: 00007f5e4dd3edc4
  R10: 0000000000000001  R11: 0000000000000246  R12: ffffffff8105eb81
  R13: 00007f5e4dd3ed30  R14: 00007f5e4dd3f2f0  R15: 0000000000000000
  ORIG_RAX: 0000000000000062  CS: 0033  SS: 002b

Basically the same problem was found earlier in kernel vmlinux-2.6.32.12-0.7-default.gz.

This patch was tested on 2.6.32 (as some kernel modules we need
require it) and the computation ran for more than 35 days without
any problems, before it would crash after 19 days of that ricc2 computation.

Signed-off-by: Fawzi Mohamed <fawzi@xxxxxx>
Signed-off-by: Thomas Dargel <td@xxxxxxxxxxxxxxxxxxxx>
Tested-by: Thomas Dargel <td@xxxxxxxxxxxxxxxxxxxx>
Cc: Hillf Danton <dhillf@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/sched/core.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4603b9d..03a2d89 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2966,7 +2966,7 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
 		u64 temp = (__force u64) rtime;
 
 		temp *= (__force u64) utime;
-		do_div(temp, (__force u32) total);
+		temp = div64_u64(temp, total);
 		utime = (__force cputime_t) temp;
 	} else
 		utime = rtime;
@@ -2999,7 +2999,7 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
 		u64 temp = (__force u64) rtime;
 
 		temp *= (__force u64) cputime.utime;
-		do_div(temp, (__force u32) total);
+		temp = div64_u64(temp, total);
 		utime = (__force cputime_t) temp;
 	} else
 		utime = rtime;
-- 
1.7.0.4

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