PCI: pci_get_device call from interrupt in reboot fixups

The following calltrace is possible now:
 handle_sysrq
   machine_emergency_restart
     mach_reboot_fixups
       pci_get_device
         pci_get_subsys
	   down_read
The patch skips reboot fixup if called from sysrq-B code.
Signed-off-by: NDenis V. Lunev <den@openvz.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

arch/x86/kernel/reboot_fixups_32.c

@@ -11,6 +11,7 @@
 
 #include <asm/delay.h>
 #include <linux/pci.h>
+#include <linux/interrupt.h>
 #include <asm/reboot_fixups.h>
 #include <asm/msr.h>
 
@@ -56,6 +57,11 @@ void mach_reboot_fixups(void)
 	struct pci_dev *dev;
 	int i;
 
+	/* we can be called from sysrq-B code. In such a case it is
+	 * prohibited to dig PCI */
+	if (in_interrupt())
+		return;
+
 	for (i=0; i < ARRAY_SIZE(fixups_table); i++) {
 		cur = &(fixups_table[i]);
 		dev = pci_get_device(cur->vendor, cur->device, NULL);