From: Xunlei Pang Currently dl tasks will actually return at the very beginning of rt_mutex_adjust_prio_chain() in !detect_deadlock cases: if (waiter->prio == task->prio) { if (!detect_deadlock) goto out_unlock_pi; // out here else requeue = false; } As the deadline value of blocked deadline tasks(waiters) without changing their sched_class(thus prio doesn't change) never changes, this seems reasonable, but it actually misses the chance of updating rt_mutex_waiter's "dl_runtime(period)_copy" if a waiter updates its deadline parameters(dl_runtime, dl_period) or boosted waiter changes to !deadline class. Thus, force deadline task not out by adding the !dl_prio() condition. [peterz: I should introduce more task state comparators like rt_mutex_waiter_less, all PI prio comparisons already have this DL exception, except this one] Cc: Steven Rostedt Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Juri Lelli Signed-off-by: Xunlei Pang Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/1460633827-345-7-git-send-email-xlpang@redhat.com --- kernel/locking/rtmutex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -488,7 +488,7 @@ static int rt_mutex_adjust_prio_chain(st * enabled we continue, but stop the requeueing in the chain * walk. */ - if (waiter->prio == task->prio) { + if (waiter->prio == task->prio && !dl_task(task)) { if (!detect_deadlock) goto out_unlock_pi; else