do_generic_file_read(): fail immediately if killed

If a fatal signal has been received, fail immediately instead of trying
to read more data.

If wait_on_page_locked_killable() was interrupted then this page is most
likely is not PageUptodate() and in this case do_generic_file_read()
will fail after lock_page_killable().

See also commit ebded027 ("mm: filemap: avoid unnecessary calls to
lock_page when waiting for IO to complete during a read")

[oleg@redhat.com: changelog addition]
Link: http://lkml.kernel.org/r/63068e8e-8bee-b208-8441-a3c39a9d9eb6@sandisk.comSigned-off-by: NBart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Acked-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -1721,7 +1721,9 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
 			 * wait_on_page_locked is used to avoid unnecessarily
 			 * serialisations and why it's safe.
 			 */
-			wait_on_page_locked_killable(page);
+			error = wait_on_page_locked_killable(page);
+			if (unlikely(error))
+				goto readpage_error;
 			if (PageUptodate(page))
 				goto page_ok;