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@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/20190730223828.600085866@linutronix.de

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 6a6fc8a..48305ba 100644 (file)
--- 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);
        }
 
        /*