bcache: Add on error panic/unregister setting

Works kind of like the ext4 setting, to panic or remount read only on
errors.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index fd37342..74f2e90 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1260,7 +1260,8 @@
 {
 	va_list args;
 
-	if (test_bit(CACHE_SET_STOPPING, &c->flags))
+	if (c->on_error != ON_ERROR_PANIC &&
+	    test_bit(CACHE_SET_STOPPING, &c->flags))
 		return false;
 
 	/* XXX: we can be called from atomic context
@@ -1275,6 +1276,9 @@
 
 	printk(", disabling caching\n");
 
+	if (c->on_error == ON_ERROR_PANIC)
+		panic("panic forced after error\n");
+
 	bch_cache_set_unregister(c);
 	return true;
 }