[tip:timers/core] itimers: Prepare for PREEMPT_RT

[tip-bot for Anna-Maria Gleixner <tipbot@zytor.com>]

Commit-ID:  c7e6d704a0097e59667495cf52dcc4e1085e620b
Gitweb:     https://git.kernel.org/tip/c7e6d704a0097e59667495cf52dcc4e1085e620b
Author:     Anna-Maria Gleixner <anna-maria@linutronix.de>
AuthorDate: Wed, 31 Jul 2019 00:33:51 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 1 Aug 2019 20:51:24 +0200

itimers: Prepare for PREEMPT_RT

Use the hrtimer_cancel_wait_running() synchronization mechanism to prevent
priority inversion and live locks on PREEMPT_RT.

As a benefit the retry loop gains the missing cpu_relax() on !RT.

[ tglx: Split out of combo patch ]

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190730223828.690771827@linutronix.de


---
 kernel/time/itimer.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index 02068b2d5862..9d26fd4ba4c0 100644
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -213,6 +213,7 @@ again:
 		/* We are sharing ->siglock with it_real_fn() */
 		if (hrtimer_try_to_cancel(timer) < 0) {
 			spin_unlock_irq(&tsk->sighand->siglock);
+			hrtimer_cancel_wait_running(timer);
 			goto again;
 		}
 		expires = timeval_to_ktime(value->it_value);