Re: [patch] 2.6.5 BUG if smp_call_function is called with interrupts disabled

[Keith Owens <kaos@sgi.com>]

Take 3.

There is a nasty race if smp_call_function() is called with interrupts
disabled.

CPU A                               CPU B
Disable interrupts
                                    smp_call_function()
                                    Take call_lock
                                    Send IPIs
                                    Wait for all cpus to acknowledge IPI
                                    CPU A has not responded, spin waiting
                                    for cpu A to respond, holding call_lock
smp_call_function()
Spin waiting for call_lock
Deadlock                            Deadlock

This bug is hard to reproduce and even harder to diagnose.  Since the
comments at the start of smp_call_function() say it should never be
entered with interrupts disabled, make it so.

Index: linux/arch/ia64/kernel/smp.c
=================================--- linux.orig/arch/ia64/kernel/smp.c	Mon Apr 26 15:20:17 2004
+++ linux/arch/ia64/kernel/smp.c	Tue Apr 27 11:30:48 2004
@@ -323,6 +323,8 @@
 	if (!cpus)
 		return 0;
 
+	BUG_ON(irqs_disabled());
+
 	data.func = func;
 	data.info = info;
 	atomic_set(&data.started, 0);