[PATCH] uml: SIGIO locking comment

Comment the use of a mysterious-looking lock.
Signed-off-by: NJeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/sigio.c

@@ -42,6 +42,7 @@ int write_sigio_irq(int fd)
 	return(0);
 }
 
+/* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
 static DEFINE_SPINLOCK(sigio_spinlock);
 
 void sigio_lock(void)