[S390] magic sysrq: check for in_atomic before doing an console_unblank

When doing an magic sysrq reboot on s390 the following bug message
appears:

SysRq : Resetting
BUG: sleeping function called from invalid context at include/asm/semaphore.h:61

in_atomic():1, irqs_disabled():0
07000000004002a8 000000000fe6bc48 0000000000000002 0000000000000000
       000000000fe6bce8 000000000fe6bc60 000000000fe6bc60 000000000012a79a
       0000000000000000 07000000004002a8 0000000000000006 0000000000000000
       0000000000000000 000000000fe6bc48 000000000000000d 000000000fe6bcb8
       00000000004000c8 0000000000103234 000000000fe6bc48 000000000fe6bc90
Call Trace:
(¬<00000000001031b2>| show_trace+0x12e/0x148)
 ¬<000000000011ffca>| __might_sleep+0x10a/0x118
 ¬<0000000000129fba>| acquire_console_sem+0x92/0xf4
 ¬<000000000012a2ca>| console_unblank+0xc2/0xc8
 ¬<0000000000107bb4>| machine_restart+0x54/0x6c
 ¬<000000000028e806>| sysrq_handle_reboot+0x26/0x30
 ¬<000000000028e52a>| __handle_sysrq+0xa6/0x180
 ¬<0000000000140134>| run_workqueue+0xcc/0x18c
 ¬<000000000014029a>| worker_thread+0xa6/0x108
 ¬<00000000001458e4>| kthread+0x64/0x9c
 ¬<0000000000106f0e>| kernel_thread_starter+0x6/0xc
 ¬<0000000000106f08>| kernel_thread_starter+0x0/0xc

The only reason for doing a console_unblank on s390 is to flush the
log buffer. We have to check for in_atomic before doing a
console_unblank as the console is otherwise filled with an unrelated
bug message.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/setup.c

@@ -347,7 +347,7 @@ void (*_machine_power_off)(void) = do_machine_power_off_nonsmp;
 
 void machine_restart(char *command)
 {
-	if (!in_interrupt() || oops_in_progress)
+	if ((!in_interrupt() && !in_atomic()) || oops_in_progress)
 		/*
 		 * Only unblank the console if we are called in enabled
 		 * context or a bust_spinlocks cleared the way for us.