ubifs: master area fails to recover when master node 1 is corrupted

[Ryder Wang]

Hi,

I just find that master area will always fail to recover while mounting, when master node 1's CRC is corrupted but master node 2 is completely good.  It can be 100% reproduced on Kernel v5.4.233, but it seems a common issue.

How to reproduce it:
1. Corrupt the CRC value of master node 1 (keep master node 2 is good) on ubifs.
2. Mount this ubifs. 

Mount at step#2 will always fail. From the log, it looks master recovering fails, but master recovering is expected to be OK in such case.

Below is the kernel log of this failure:

ubifs_mount:2253: UBIFS DBG gen (pid 10770): name ubi0:test_volume, flags 0x0
ubifs_mount:2274: UBIFS DBG gen (pid 10770): opened ubi0_0
ubifs_read_node:1094: UBIFS DBG io (pid 10770): LEB 0:0, superblock node, length 4096
UBIFS (ubi0:0): Mounting in unauthenticated mode
ubifs_read_superblock:765: UBIFS DBG mnt (pid 10770): Auto resizing from 13 LEBs to 100 LEBs
ubifs_start_scan:131: UBIFS DBG scan (pid 10770): scan LEB 1:0
ubifs_scan:270: UBIFS DBG scan (pid 10770): look at LEB 1:0 (253952 bytes left)
ubifs_scan_a_node:77: UBIFS DBG scan (pid 10770): scanning master node at LEB 1:0
UBIFS error (ubi0:0 pid 10770): ubifs_scan [ubifs]: bad node
ubifs_recover_master_node:234: UBIFS DBG rcvry (pid 10770): recovery
ubifs_scan_a_node:77: UBIFS DBG scan (pid 10770): scanning master node at LEB 1:0
get_master_node:163: UBIFS DBG rcvry (pid 10770): found corruption at 1:0
ubifs_scan_a_node:77: UBIFS DBG scan (pid 10770): scanning master node at LEB 2:0
get_master_node:152: UBIFS DBG rcvry (pid 10770): found a master node at 2:0
UBIFS error (ubi0:0 pid 10770): ubifs_recover_master_node [ubifs]: failed to recover master node
UBIFS error (ubi0:0 pid 10770): ubifs_recover_master_node [ubifs]: dumping second master node
UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 10772
        magic          0x6101831
        crc            0x3a5c03b2
        node_type      7 (master node)
        group_type     0 (no node group)
        sqnum          9
        len            512
        highest_inum   65
        commit number  0
        flags          0x2
        log_lnum       3
        root_lnum      12
        root_offs      0
        root_len       108
        gc_lnum        11
        ihead_lnum     12
        ihead_offs     4096
        index_size     112
        lpt_lnum       7
        lpt_offs       44
        nhead_lnum     7
        nhead_offs     4096
        ltab_lnum      7
        ltab_offs      57
        lsave_lnum     0
        lsave_offs     0
        lscan_lnum     10
        leb_cnt        13
        empty_lebs     1
        idx_lebs       1
        total_free     753664
        total_dirty    7640
        total_used     440
        total_dead     0
        total_dark     16384
UBIFS (ubi0:0): background thread "ubifs_bgt0_0" stops