• OGAWA Hirofumi's avatar
    jbd2: fix FS corruption possibility in jbd2_journal_destroy() on umount path · 73ce783d
    OGAWA Hirofumi authored
    commit c0a2ad9b upstream.
    
    On umount path, jbd2_journal_destroy() writes latest transaction ID
    (->j_tail_sequence) to be used at next mount.
    
    The bug is that ->j_tail_sequence is not holding latest transaction ID
    in some cases. So, at next mount, there is chance to conflict with
    remaining (not overwritten yet) transactions.
    
    	mount (id=10)
    	write transaction (id=11)
    	write transaction (id=12)
    	umount (id=10) <= the bug doesn't write latest ID
    
    	mount (id=10)
    	write transaction (id=11)
    	crash
    
    	mount
    	[recovery process]
    		transaction (id=11)
    		transaction (id=12) <= valid transaction ID, but old commit
                                           must not replay
    
    Like above, this bug become the cause of recovery failure, or FS
    corruption.
    
    So why ->j_tail_sequence doesn't point latest ID?
    
    Because if checkpoint transactions was reclaimed by memory pressure
    (i.e. bdev_try_to_free_page()), then ->j_tail_sequence is not updated.
    (And another case is, __jbd2_journal_clean_checkpoint_list() is called
    with empty transaction.)
    
    So in above cases, ->j_tail_sequence is not pointing latest
    transaction ID at umount path. Plus, REQ_FLUSH for checkpoint is not
    done too.
    
    So, to fix this problem with minimum changes, this patch updates
    ->j_tail_sequence, and issue REQ_FLUSH.  (With more complex changes,
    some optimizations would be possible to avoid unnecessary REQ_FLUSH
    for example though.)
    
    BTW,
    
    	journal->j_tail_sequence =
    		++journal->j_transaction_sequence;
    
    Increment of ->j_transaction_sequence seems to be unnecessary, but
    ext3 does this.
    Signed-off-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
    73ce783d
journal.c 74.9 KB