dm verity: skip verity work if I/O error when system is shutting down

If emergency system shutdown is called, like by thermal shutdown,
a dm device could be alive when the block device couldn't process
I/O requests anymore. In this state, the handling of I/O errors
by new dm I/O requests or by those already in-flight can lead to
a verity corruption state, which is a misjudgment.

So, skip verity work in response to I/O error when system is shutting
down.

Signed-off-by: Hyeongseok Kim <[e-mail]>
Reviewed-by: Sami Tolvanen <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-verity-target.c

···
 }
 
 /*
+ * Skip verity work in response to I/O error when system is shutting down.
+ */
+static inline bool verity_is_system_shutting_down(void)
+{
+	return system_state == SYSTEM_HALT || system_state == SYSTEM_POWER_OFF
+		|| system_state == SYSTEM_RESTART;
+}
+
+/*
  * End one "io" structure with a given error.
  */
 static void verity_finish_io(struct dm_verity_io *io, blk_status_t status)
···
 {
 	struct dm_verity_io *io = bio->bi_private;
 
-	if (bio->bi_status && !verity_fec_is_enabled(io->v)) {
+	if (bio->bi_status &&
+	    (!verity_fec_is_enabled(io->v) || verity_is_system_shutting_down())) {
 		verity_finish_io(io, bio->bi_status);
 		return;
 	}