Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

Pull scheduler fixes from Ingo Molnar:
 "This fixes the cputime scaling overflow problems for good without
  having bad 32-bit overhead, and gets rid of the div64_u64_rem() helper
  as well."

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  Revert "math64: New div64_u64_rem helper"
  sched: Avoid prev->stime underflow
  sched: Do not account bogus utime
  sched: Avoid cputime scaling overflow

diff --combined kernel/sched/cputime.c
index ea32f02,337a367..cc2dc3e
--- 1/kernel/sched/cputime.c
--- 2/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@@ -294,7 -294,7 +294,7 @@@ void thread_group_cputime(struct task_s
  
        t = tsk;
        do {
 -              task_cputime(tsk, &utime, &stime);
 +              task_cputime(t, &utime, &stime);
                times->utime += utime;
                times->stime += stime;
                times->sum_exec_runtime += task_sched_runtime(t);
@@@ -506,34 -506,47 +506,47 @@@ void account_idle_ticks(unsigned long t
  }
  
  /*
-  * Perform (stime * rtime) / total with reduced chances
-  * of multiplication overflows by using smaller factors
-  * like quotient and remainders of divisions between
-  * rtime and total.
+  * Perform (stime * rtime) / total, but avoid multiplication overflow by
+  * loosing precision when the numbers are big.
   */
  static cputime_t scale_stime(u64 stime, u64 rtime, u64 total)
  {
-       u64 rem, res, scaled;
+       u64 scaled;
  
-       if (rtime >= total) {
-               /*
-                * Scale up to rtime / total then add
-                * the remainder scaled to stime / total.
-                */
-               res = div64_u64_rem(rtime, total, &rem);
-               scaled = stime * res;
-               scaled += div64_u64(stime * rem, total);
-       } else {
-               /*
-                * Same in reverse: scale down to total / rtime
-                * then substract that result scaled to
-                * to the remaining part.
-                */
-               res = div64_u64_rem(total, rtime, &rem);
-               scaled = div64_u64(stime, res);
-               scaled -= div64_u64(scaled * rem, total);
+       for (;;) {
+               /* Make sure "rtime" is the bigger of stime/rtime */
+               if (stime > rtime) {
+                       u64 tmp = rtime; rtime = stime; stime = tmp;
+               }
+ 
+               /* Make sure 'total' fits in 32 bits */
+               if (total >> 32)
+                       goto drop_precision;
+ 
+               /* Does rtime (and thus stime) fit in 32 bits? */
+               if (!(rtime >> 32))
+                       break;
+ 
+               /* Can we just balance rtime/stime rather than dropping bits? */
+               if (stime >> 31)
+                       goto drop_precision;
+ 
+               /* We can grow stime and shrink rtime and try to make them both fit */
+               stime <<= 1;
+               rtime >>= 1;
+               continue;
+ 
+ drop_precision:
+               /* We drop from rtime, it has more bits than stime */
+               rtime >>= 1;
+               total >>= 1;
        }
  
+       /*
+        * Make sure gcc understands that this is a 32x32->64 multiply,
+        * followed by a 64/32->64 divide.
+        */
+       scaled = div_u64((u64) (u32) stime * (u64) (u32) rtime, (u32)total);
        return (__force cputime_t) scaled;
  }
  
@@@ -545,7 -558,7 +558,7 @@@ static void cputime_adjust(struct task_
                           struct cputime *prev,
                           cputime_t *ut, cputime_t *st)
  {
-       cputime_t rtime, stime, total;
+       cputime_t rtime, stime, utime, total;
  
        if (vtime_accounting_enabled()) {
                *ut = curr->utime;
@@@ -568,13 -581,21 +581,21 @@@
         */
        rtime = nsecs_to_cputime(curr->sum_exec_runtime);
  
-       if (!rtime) {
-               stime = 0;
-       } else if (!total) {
-               stime = rtime;
-       } else {
+       /*
+        * Update userspace visible utime/stime values only if actual execution
+        * time is bigger than already exported. Note that can happen, that we
+        * provided bigger values due to scaling inaccuracy on big numbers.
+        */
+       if (prev->stime + prev->utime >= rtime)
+               goto out;
+ 
+       if (total) {
                stime = scale_stime((__force u64)stime,
                                    (__force u64)rtime, (__force u64)total);
+               utime = rtime - stime;
+       } else {
+               stime = rtime;
+               utime = 0;
        }
  
        /*
@@@ -583,8 -604,9 +604,9 @@@
         * Let's enforce monotonicity.
         */
        prev->stime = max(prev->stime, stime);
-       prev->utime = max(prev->utime, rtime - prev->stime);
+       prev->utime = max(prev->utime, utime);
  
+ out:
        *ut = prev->utime;
        *st = prev->stime;
  }