sched/fair: Fix multiplication overflow on 32-bit systems

Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX'
on 32-bit systems:

	UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18
	signed integer overflow:
	87950 * 47742 cannot be represented in type 'int'

The most likely effect of this bug are bad load average numbers
resulting in weird scheduling. It's also likely that this can
persist for a longer time - until the system goes idle for
a long time so that all load avg numbers get reset.

[ This is the CFS load average metric, not the procfs output, which
  is separate. ]

Signed-off-by: Andrey Ryabinin <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
Link: http://lkml.kernel.org/r/[email protected]
[ Improved the changelog. ]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 90e26b11deaa1ab4b78302605850523a7852720b..cfdc0e61066c20b926e0d5ca7ed5d9732a1c903b 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2689,7 +2689,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
        int decayed, removed = 0;
 
        if (atomic_long_read(&cfs_rq->removed_load_avg)) {
-               long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
+               s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
                sa->load_avg = max_t(long, sa->load_avg - r, 0);
                sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
                removed = 1;