mm: skip swap readahead when process is exiting

It's possible for a user fault to be triggered during task exit that
results in swap readahead, which is not useful. Skip swap readahead
if the current process is exiting.

Change-Id: I5fad20ebdcc616af732254705726d395eb118cbe
Signed-off-by: Tim Murray <timmurray@google.com>

I know swap is not used with my kernel.
Just picking for future references.

Signed-off-by: Park Ju Hyung <qkrwngud825@gmail.com>
Signed-off-by: Raphiel Rollerscaperers <rapherion@raphielgang.org>
Signed-off-by: DennySPB <dennyspb@gmail.com>
Signed-off-by: Chenyang Zhong <zhongcy95@gmail.com>

mm/swap_state.c

@@ -483,6 +483,10 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	if (!mask)
 		goto skip;
 
+	/* If exiting, don't do swap readahead. */
+	if (current->flags & PF_EXITING)
+		goto skip;
+
 	/* Read a page_cluster sized and aligned cluster around offset. */
 	start_offset = offset & ~mask;
 	end_offset = offset | mask;