uprobes: wait for mmap_sem for write killable

xol_add_vma needs mmap_sem for write.  If the waiting task gets killed
by the oom killer it would block oom_reaper from asynchronous address
space reclaim and reduce the chances of timely OOM resolving.  Wait for
the lock in the killable mode and return with EINTR if the task got
killed while waiting.

Do not warn in dup_xol_work if __create_xol_area failed due to fatal
signal pending because this is usually considered a kernel issue.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/events/uprobes.c

@@ -1130,7 +1130,9 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
 	struct vm_area_struct *vma;
 	int ret;
 
-	down_write(&mm->mmap_sem);
+	if (down_write_killable(&mm->mmap_sem))
+		return -EINTR;
+
 	if (mm->uprobes_state.xol_area) {
 		ret = -EALREADY;
 		goto fail;
@@ -1469,7 +1471,8 @@ static void dup_xol_work(struct callback_head *work)
 	if (current->flags & PF_EXITING)
 		return;
 
-	if (!__create_xol_area(current->utask->dup_xol_addr))
+	if (!__create_xol_area(current->utask->dup_xol_addr) &&
+			!fatal_signal_pending(current))
 		uprobe_warn(current, "dup xol area");
 }