From: Xunlei Pang Date: Thu, 14 Apr 2016 12:19:28 +0000 (+0800) Subject: sched/deadline: Fix a bug in dl_overflow() X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=fec148c000d0f9ac21679601722811eb60b4cc52;p=deliverable%2Flinux.git sched/deadline: Fix a bug in dl_overflow() I got a minus(very big) dl_b->total_bw during my deadline tests. # grep dl /proc/sched_debug dl_rq[0]: .dl_nr_running : 0 .dl_bw->bw : 996147 .dl_bw->total_bw : -222297900 Something unusual must have happened. After some digging, I finally noticed that when changing a deadline task to normal(cfs), and changing it back to deadline immediately, after it died, we will got the wrong dl_bw->total_bw. The root cause is in dl_overflow(), it has: if (new_bw == p->dl.dl_bw) return 0; 1) When a deadline task is changed to !deadline task, it will start dl timer in switched_from_dl(), and retain previous deadline parameter till the timer expires. 2) If we change it back to deadline with the same bandwidth parameter before the timer expires, as it keeps the old bandwidth although it is not a deadline task. dl_overflow() simply returns success without updating the right data, and got the wrong dl_bw->total_bw. The solution is simple, if @p is not deadline, don't return. Signed-off-by: Xunlei Pang Signed-off-by: Peter Zijlstra (Intel) Acked-by: Juri Lelli Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1460636368-1993-1-git-send-email-xlpang@redhat.com Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 71dffbb27ce6..9d84d6004745 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2378,7 +2378,8 @@ static int dl_overflow(struct task_struct *p, int policy, u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0; int cpus, err = -1; - if (new_bw == p->dl.dl_bw) + /* !deadline task may carry old deadline bandwidth */ + if (new_bw == p->dl.dl_bw && task_has_dl_policy(p)) return 0; /*