sysrq: add commentary on why we use the console loglevel over using KERN_EMERG

Add an explanitory comment as to why we modify the kernel console loglevel
rather than simply moving sysrq messages to KERN_EMERG level.
Signed-off-by: NAndy Whitcroft <apw@canonical.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/sysrq.c

@@ -473,6 +473,12 @@ void __handle_sysrq(int key, struct tty_struct *tty, int check_mask)
 	unsigned long flags;
 
 	spin_lock_irqsave(&sysrq_key_table_lock, flags);
+	/*
+	 * Raise the apparent loglevel to maximum so that the sysrq header
+	 * is shown to provide the user with positive feedback.  We do not
+	 * simply emit this at KERN_EMERG as that would change message
+	 * routing in the consumers of /proc/kmsg.
+	 */
 	orig_log_level = console_loglevel;
 	console_loglevel = 7;
 	printk(KERN_INFO "SysRq : ");