[PATCH] stop_machine() vs. synchronous IPI send deadlock

[Kirill Korotaev]

Hello Andrew,

This patch fixes deadlock of stop_machine() vs. synchronous IPI send.
The problem is that stop_machine() disables interrupts before disabling 
preemption on other CPUs. So if another CPU is preempted and then calls 
something like flush_tlb_all() it will deadlock with CPU doing 
stop_machine() and which can't process IPI due to disabled IRQs.

I changed stop_machine() to do the same things exactly as it does on 
other CPUs, i.e. it should disable preemption first on _all_ CPUs 
including itself and only after that disable IRQs.

Signed-Off-By: Kirill Korotaev <dev@xxxxx>

Kirill
--- ./kernel/stop_machine.c.stpmach	2005-11-01 12:06:03.000000000 +0300
+++ ./kernel/stop_machine.c	2005-11-09 13:58:03.000000000 +0300
@@ -114,13 +114,12 @@ static int stop_machine(void)
 		return ret;
 	}
 
-	/* Don't schedule us away at this point, please. */
-	local_irq_disable();
-
 	/* Now they are all started, make them hold the CPUs, ready. */
+	preempt_disable();
 	stopmachine_set_state(STOPMACHINE_PREPARE);
 
 	/* Make them disable irqs. */
+	local_irq_disable();
 	stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
 
 	return 0;