mm, gup: return EINTR when gup is interrupted by fatal signals

EINTR is the usual error code which other killable interfaces return.
This is the case for the other fatal_signal_pending break out from the
same function.  Make the code consistent.

ERESTARTSYS is also quite confusing because the signal is fatal and so
no restart will happen before returning to the userspace.
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Link: http://lkml.kernel.org/r/20200409071133.31734-1-mhocko@kernel.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -1088,7 +1088,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		 * potentially allocating memory.
 		 */
 		if (fatal_signal_pending(current)) {
-			ret = -ERESTARTSYS;
+			ret = -EINTR;
 			goto out;
 		}
 		cond_resched();