ARM: 7417/1: vfp: ensure preemption is disabled when enabling VFP access

The vfp_enable function enables access to the VFP co-processor register
space (cp10 and cp11) on the current CPU and must be called with
preemption disabled. Unfortunately, the vfp_init late initcall does not
disable preemption and can lead to an oops during boot if thread
migration occurs at the wrong time and we end up attempting to access
the FPSID on a CPU with VFP access disabled.

This patch fixes the initcall to call vfp_enable from a non-preemptible
context on each CPU and adds a BUG_ON(preemptible) to ensure that any
similar problems are easily spotted in the future.

Cc: stable@vger.kernel.org
Reported-by: Hyungwoo Yang <hwoo.yang@gmail.com>
Signed-off-by: Hyungwoo Yang <hyungwooy@nvidia.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/vfp/vfpmodule.c

@@ -11,6 +11,7 @@
 #include <linux/types.h>
 #include <linux/cpu.h>
 #include <linux/cpu_pm.h>
+#include <linux/hardirq.h>
 #include <linux/kernel.h>
 #include <linux/notifier.h>
 #include <linux/signal.h>
@@ -432,7 +433,10 @@ void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs)
 
 static void vfp_enable(void *unused)
 {
-	u32 access = get_copro_access();
+	u32 access;
+
+	BUG_ON(preemptible());
+	access = get_copro_access();
 
 	/*
 	 * Enable full access to VFP (cp10 and cp11)
@@ -657,7 +661,7 @@ static int __init vfp_init(void)
 	unsigned int cpu_arch = cpu_architecture();
 
 	if (cpu_arch >= CPU_ARCH_ARMv6)
-		vfp_enable(NULL);
+		on_each_cpu(vfp_enable, NULL, 1);
 
 	/*
 	 * First check that there is a VFP that we can use.
@@ -678,8 +682,6 @@ static int __init vfp_init(void)
 	} else {
 		hotcpu_notifier(vfp_hotplug, 0);
 
-		smp_call_function(vfp_enable, NULL, 1);
-
 		VFP_arch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;  /* Extract the architecture version */
 		printk("implementor %02x architecture %d part %02x variant %x rev %x\n",
 			(vfpsid & FPSID_IMPLEMENTER_MASK) >> FPSID_IMPLEMENTER_BIT,