[PATCH 1/1] ubifs: Try to recover from missing znode

Benedikt Spranger
2024-10-08T13:41:09Z

After powercut on a system using ubifs mounting failed:

2024-09-30T12:38:26.880487+02:00 sonja kernel: UBIFS error (ubi0:0 pid 2178): ubifs_read_node [ubifs]: bad node type (255 but expected 9)
2024-09-30T12:38:26.880506+02:00 sonja kernel: UBIFS error (ubi0:0 pid 2178): ubifs_read_node [ubifs]: bad node at LEB 103:46920, LEB mapping status 0
2024-09-30T12:38:26.880509+02:00 sonja kernel: Not a node, first 24 bytes:
2024-09-30T12:38:26.880510+02:00 sonja kernel: 00000000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ........................

While traversing over zbranches during the journal replay one zbranch
points to a znode, which was not written to the flash and therefore the
flash is empty.

Try to recover from that by inserting an empty znode instead of failing.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
---
fs/ubifs/io.c | 16 ++++++++++++++++
fs/ubifs/tnc_misc.c | 6 +++++-
2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c
index 01d8eb170382..0bbb426f9006 100644
--- a/fs/ubifs/io.c
+++ b/fs/ubifs/io.c
@@ -1110,6 +1110,22 @@ int ubifs_read_node(const struct ubifs_info *c, void *buf, int type, int len,
return err;

if (type != ch->node_type) {
+ /*
+ * While recovering, we may face lost data i.e. empty flash.
+ * Give callsites a hint by returning -ENODATA.
+ */
+ if (c->replaying) {
+ u8 *b = buf;
+
+ for (l = 0; l < len; l++) {
+ if (b[l] != 0xff)
+ break;
+ }
+ if (l == len) {
+ ubifs_errc(c, "no node, but empty flash");
+ return -ENODATA;
+ }
+ }
ubifs_errc(c, "bad node type (%d but expected %d)",
ch->node_type, type);
goto out;
diff --git a/fs/ubifs/tnc_misc.c b/fs/ubifs/tnc_misc.c
index d3f8a6aa1f49..4d085fc1300f 100644
--- a/fs/ubifs/tnc_misc.c
+++ b/fs/ubifs/tnc_misc.c
@@ -300,7 +300,11 @@ static int read_znode(struct ubifs_info *c, struct ubifs_zbranch *zzbr,
err = ubifs_read_node(c, idx, UBIFS_IDX_NODE, len, lnum, offs);
if (err < 0) {
kfree(idx);
- return err;
+ /*
+ * While recovering we may face a non written znode.
+ * Inject an empty znode in this case.
+ */
+ return (err == -ENODATA) ? 0 : err;
}

err = ubifs_node_check_hash(c, idx, zzbr->hash);
--
2.39.5