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

[tip-bot for Anna-Maria Gleixner]

Commit-ID:  4da1306fb920a267b5ea21ee15cd771c7bc09cc6
Gitweb:     https://git.kernel.org/tip/4da1306fb920a267b5ea21ee15cd771c7bc09cc6
Author:     Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
AuthorDate: Wed, 31 Jul 2019 00:33:50 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 1 Aug 2019 17:46:41 +0200

timerfd: Prepare for PREEMPT_RT

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

[ tglx: Split out of combo patch ]

Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190730223828.600085866@xxxxxxxxxxxxx

---
 fs/timerfd.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 6a6fc8aa1de7..48305ba41e3c 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -471,7 +471,11 @@ static int do_timerfd_settime(int ufd, int flags,
 				break;
 		}
 		spin_unlock_irq(&ctx->wqh.lock);
-		cpu_relax();
+
+		if (isalarm(ctx))
+			hrtimer_cancel_wait_running(&ctx->t.alarm.timer);
+		else
+			hrtimer_cancel_wait_running(&ctx->t.tmr);
 	}
 
 	/*