• Andreas Rohner's avatar
    nilfs2: fix segctor bug that causes file system corruption · 70f2fe3a
    Andreas Rohner authored
    There is a bug in the function nilfs_segctor_collect, which results in
    active data being written to a segment, that is marked as clean.  It is
    possible, that this segment is selected for a later segment
    construction, whereby the old data is overwritten.
    
    The problem shows itself with the following kernel log message:
    
      nilfs_sufile_do_cancel_free: segment 6533 must be clean
    
    Usually a few hours later the file system gets corrupted:
    
      NILFS: bad btree node (blocknr=8748107): level = 0, flags = 0x0, nchildren = 0
      NILFS error (device sdc1): nilfs_bmap_last_key: broken bmap (inode number=114660)
    
    The issue can be reproduced with a file system that is nearly full and
    with the cleaner running, while some IO intensive task is running.
    Although it is quite hard to reproduce.
    
    This is what happens:
    
     1. The cleaner starts the segment construction
     2. nilfs_segctor_collect is called
     3. sc_stage is on NILFS_ST_SUFILE and segments are freed
     4. sc_stage is on NILFS_ST_DAT current segment is full
     5. nilfs_segctor_extend_segments is called, which
        allocates a new segment
     6. The new segment is one of the segments freed in step 3
     7. nilfs_sufile_cancel_freev is called and produces an error message
     8. Loop around and the collection starts again
     9. sc_stage is on NILFS_ST_SUFILE and segments are freed
        including the newly allocated segment, which will contain active
        data and can be allocated at a later time
    10. A few hours later another segment construction allocates the
        segment and causes file system corruption
    
    This can be prevented by simply reordering the statements.  If
    nilfs_sufile_cancel_freev is called before nilfs_segctor_extend_segments
    the freed segments are marked as dirty and cannot be allocated any more.
    Signed-off-by: default avatarAndreas Rohner <andreas.rohner@gmx.net>
    Reviewed-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Tested-by: default avatarAndreas Rohner <andreas.rohner@gmx.net>
    Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    70f2fe3a
segment.c 71.5 KB