[PATCH] alpha: fix kernel panic during SysRq-b

acquire_console_sem() does BUG() in interrupt context now, as in the case
of SysRq-b.

Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/alpha/kernel/process.c

@@ -127,6 +127,10 @@ common_shutdown_1(void *generic_ptr)
 	/* If booted from SRM, reset some of the original environment. */
 	if (alpha_using_srm) {
 #ifdef CONFIG_DUMMY_CONSOLE
+		/* If we've gotten here after SysRq-b, leave interrupt
+		   context before taking over the console. */
+		if (in_interrupt())
+			irq_exit();
 		/* This has the effect of resetting the VGA video origin.  */
 		take_over_console(&dummy_con, 0, MAX_NR_CONSOLES-1, 1);
 #endif