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

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Message-Id: <20241008133342.1937674-1-b.spranger@linutronix.de>
Date: Tue,  8 Oct 2024 15:33:42 +0200
From: Benedikt Spranger <b.spranger@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: linux-mtd@...ts.infradead.org,
	Zhihao Cheng <chengzhihao1@...wei.com>,
	Richard Weinberger <richard@....at>
Subject: [PATCH 1/1] ubifs: Try to recover from missing znode

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@...utronix.de>
Reviewed-by: John Ogness <john.ogness@...utronix.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