linux-kernel - Re: Long timeout when booting >= 2.6.38

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Message-ID: <alpine.LFD.2.02.1105161105170.3078@ionos>
Date:	Mon, 16 May 2011 11:07:48 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Christian Hoffmann <email@...istianhoffmann.info>
cc:	john stultz <johnstul@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Long timeout when booting >= 2.6.38

On Sun, 15 May 2011, Christian Hoffmann wrote:
> new trace:
> http://dl.dropbox.com/u/21820416/traceing2.log.bz2
> 
> Sorry for delay.

Nothing to be sorry about. Thanks for providing the information. If I
decoded the problem correctly then this just unearthed a real long
standing bug. Does the patch below solve the problem ?

Thanks,

	tglx

--- linux-2.6.orig/kernel/time/tick-broadcast.c
+++ linux-2.6/kernel/time/tick-broadcast.c
@@ -522,10 +522,11 @@ static void tick_broadcast_init_next_eve
  */
 void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 {
+	int cpu = smp_processor_id();
+
 	/* Set it up only once ! */
 	if (bc->event_handler != tick_handle_oneshot_broadcast) {
 		int was_periodic = bc->mode == CLOCK_EVT_MODE_PERIODIC;
-		int cpu = smp_processor_id();
 
 		bc->event_handler = tick_handle_oneshot_broadcast;
 		clockevents_set_mode(bc, CLOCK_EVT_MODE_ONESHOT);
@@ -551,6 +552,15 @@ void tick_broadcast_setup_oneshot(struct
 			tick_broadcast_set_event(tick_next_period, 1);
 		} else
 			bc->next_event.tv64 = KTIME_MAX;
+	} else {
+		/*
+		 * The first cpu which switches to oneshot mode sets
+		 * the bit for all other cpus which are in the general
+		 * (periodic) broadcast mask. So the bit is set and
+		 * would prevent the first broadcast enter after this
+		 * to program the bc device.
+		 */
+		tick_broadcast_clear_oneshot(cpu);
 	}
 }
 
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