Commit-ID: 5a8e01f8fa51f5cbce8f37acc050eb2319d12956 Gitweb: http://git.kernel.org/tip/5a8e01f8fa51f5cbce8f37acc050eb2319d12956 Author: Stanislaw Gruszka <sgrus...@redhat.com> AuthorDate: Wed, 4 Sep 2013 15:16:03 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Wed, 4 Sep 2013 16:31:25 +0200
sched/cputime: Do not scale when utime == 0 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.senozhat...@gmail.com> Signed-off-by: Stanislaw Gruszka <sgrus...@redhat.com> Cc: sta...@vger.kernel.org Cc: Frederic Weisbecker <fweis...@gmail.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> Cc: Borislav Petkov <b...@alien8.de> Link: http://lkml.kernel.org/r/20130904131602.gc2...@redhat.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/sched/cputime.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index c1d7493..5b03f5b 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -551,10 +551,7 @@ static void cputime_adjust(struct task_cputime *curr, struct cputime *prev, cputime_t *ut, cputime_t *st) { - cputime_t rtime, stime, utime, total; - - stime = curr->stime; - total = stime + curr->utime; + cputime_t rtime, stime, utime; /* * Tick based cputime accounting depend on random scheduling @@ -576,13 +573,19 @@ static void cputime_adjust(struct task_cputime *curr, 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 linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
