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authorXunlei Pang <xlpang@redhat.com>2017-03-23 15:56:07 +0100
committerThomas Gleixner <tglx@linutronix.de>2017-04-04 11:44:05 +0200
commit2a1c6029940675abb2217b590512dbf691867ec4 (patch)
treea975e4e9f643d86a904b6314a3bab21b023fd6cc /kernel/futex.c
parent38bffdac071b720db627bfd2b125a2802a04d419 (diff)
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rtmutex: Deboost before waking up the top waiter
We should deboost before waking the high-priority task, such that we don't run two tasks with the same "state" (priority, deadline, sched_class, etc). In order to make sure the boosting task doesn't start running between unlock and deboost (due to 'spurious' wakeup), we move the deboost under the wait_lock, that way its serialized against the wait loop in __rt_mutex_slowlock(). Doing the deboost early can however lead to priority-inversion if current would get preempted after the deboost but before waking our high-prio task, hence we disable preemption before doing deboost, and enabling it after the wake up is over. This gets us the right semantic order, but most importantly however; this change ensures pointer stability for the next patch, where we have rt_mutex_setprio() cache a pointer to the top-most waiter task. If we, as before this change, do the wakeup first and then deboost, this pointer might point into thin air. [peterz: Changelog + patch munging] Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Xunlei Pang <xlpang@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170323150216.110065320@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c5
1 files changed, 1 insertions, 4 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 628be42296eb..414a30dbc6b6 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1460,10 +1460,7 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
out_unlock:
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- if (deboost) {
- wake_up_q(&wake_q);
- rt_mutex_adjust_prio(current);
- }
+ rt_mutex_postunlock(&wake_q, deboost);
return ret;
}