[PATCH] update kfree, vfree, and vunmap kerneldoc

This patch clarifies NULL handling of kfree() and vfree().  I addition,
wording of calling context restriction for vfree() and vunmap() are changed
from "may not" to "must not."
Signed-off-by: NPekka Enberg <penberg@cs.helsinki.fi>
Acked-by: NManfred Spraul <manfred@colorfullife.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/slab.c

@@ -2998,6 +2998,8 @@ EXPORT_SYMBOL(kzalloc);
  * kfree - free previously allocated memory
  * @objp: pointer returned by kmalloc.
  *
+ * If @objp is NULL, no operation is performed.
+ *
  * Don't free memory not originally allocated by kmalloc()
  * or you will run into trouble.
  */

mm/vmalloc.c

@@ -332,9 +332,10 @@ void __vunmap(void *addr, int deallocate_pages)
  *	@addr:		memory base address
  *
  *	Free the virtually contiguous memory area starting at @addr, as
- *	obtained from vmalloc(), vmalloc_32() or __vmalloc().
+ *	obtained from vmalloc(), vmalloc_32() or __vmalloc(). If @addr is
+ *	NULL, no operation is performed.
  *
- *	May not be called in interrupt context.
+ *	Must not be called in interrupt context.
  */
 void vfree(void *addr)
 {
@@ -352,7 +353,7 @@ EXPORT_SYMBOL(vfree);
  *	Free the virtually contiguous memory area starting at @addr,
  *	which was created from the page array passed to vmap().
  *
- *	May not be called in interrupt context.
+ *	Must not be called in interrupt context.
  */
 void vunmap(void *addr)
 {