3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx> commit 5a8e01f8fa51f5cbce8f37acc050eb2319d12956 upstream. scale_stime() silently assumes that stime < rtime, otherwise when stime == rtime and both values are big enough (operations on them do not fit in 32 bits), the resulting scaling stime can be bigger than rtime. In consequence utime = rtime - stime results in negative value. User space visible symptoms of the bug are overflowed TIME values on ps/top, for example: $ ps aux | grep rcu root 8 0.0 0.0 0 0 ? S 12:42 0:00 [rcuc/0] root 9 0.0 0.0 0 0 ? S 12:42 0:00 [rcub/0] root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] root 11 0.1 0.0 0 0 ? S 12:42 0:02 [rcuop/0] root 12 62422329 0.0 0 0 ? S 12:42 21114581:35 [rcuop/1] root 10 62422329 0.0 0 0 ? R 12:42 21114581:37 [rcu_preempt] or overflowed utime values read directly from /proc/$PID/stat Reference: https://lkml.org/lkml/2013/8/20/259 Reported-and-tested-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Link: http://lkml.kernel.org/r/20130904131602.GC2564@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/cputime.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -558,7 +558,7 @@ static void cputime_adjust(struct task_c struct cputime *prev, cputime_t *ut, cputime_t *st) { - cputime_t rtime, stime, utime, total; + cputime_t rtime, stime, utime; if (vtime_accounting_enabled()) { *ut = curr->utime; @@ -566,9 +566,6 @@ static void cputime_adjust(struct task_c return; } - stime = curr->stime; - total = stime + curr->utime; - /* * Tick based cputime accounting depend on random scheduling * timeslices of a task to be interrupted or not by the timer. @@ -589,13 +586,19 @@ static void cputime_adjust(struct task_c if (prev->stime + prev->utime >= rtime) goto out; - if (total) { + stime = curr->stime; + utime = curr->utime; + + if (utime == 0) { + stime = rtime; + } else if (stime == 0) { + utime = rtime; + } else { + cputime_t total = stime + utime; + stime = scale_stime((__force u64)stime, (__force u64)rtime, (__force u64)total); utime = rtime - stime; - } else { - stime = rtime; - utime = 0; } /* -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html