x86: Clear irqstack thread_info

Mathias Merz reported that v2.6.37 failed to boot on his
system.

Make sure that the thread_info part of the irqstack is
initialized to zeroes.
Reported-and-Tested-by: Matthias Merz <linux@merz-ka.de>
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <AANLkTimyKXfJ1x8tgwrr1hYnNLrPfgE1NTe4z7L6tUDm@mail.gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/irq_32.c

@@ -129,8 +129,7 @@ void __cpuinit irq_ctx_init(int cpu)
 	irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
 					       THREAD_FLAGS,
 					       THREAD_ORDER));
-	irqctx->tinfo.task		= NULL;
-	irqctx->tinfo.exec_domain	= NULL;
+	memset(&irqctx->tinfo, 0, sizeof(struct thread_info));
 	irqctx->tinfo.cpu		= cpu;
 	irqctx->tinfo.preempt_count	= HARDIRQ_OFFSET;
 	irqctx->tinfo.addr_limit	= MAKE_MM_SEG(0);
@@ -140,10 +139,8 @@ void __cpuinit irq_ctx_init(int cpu)
 	irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
 					       THREAD_FLAGS,
 					       THREAD_ORDER));
-	irqctx->tinfo.task		= NULL;
-	irqctx->tinfo.exec_domain	= NULL;
+	memset(&irqctx->tinfo, 0, sizeof(struct thread_info));
 	irqctx->tinfo.cpu		= cpu;
-	irqctx->tinfo.preempt_count	= 0;
 	irqctx->tinfo.addr_limit	= MAKE_MM_SEG(0);
 
 	per_cpu(softirq_ctx, cpu) = irqctx;