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    Subject[13/91] jbd: fix fsync() tid wraparound bug
    2.6.32-longterm review patch.  If anyone has any objections, please let us know.


    From: Ted Ts'o <>

    commit d9b01934d56a96d9f4ae2d6204d4ea78a36f5f36 upstream.

    If an application program does not make any changes to the indirect
    blocks or extent tree, i_datasync_tid will not get updated. If there
    are enough commits (i.e., 2**31) such that tid_geq()'s calculations
    wrap, and there isn't a currently active transaction at the time of
    the fdatasync() call, this can end up triggering a BUG_ON in

    J_ASSERT(journal->j_running_transaction != NULL);

    It's pretty rare that this can happen, since it requires the use of
    fdatasync() plus *very* frequent and excessive use of fsync(). But
    with the right workload, it can.

    We fix this by replacing the use of tid_geq() with an equality test,
    since there's only one valid transaction id that is valid for us to
    start: namely, the currently running transaction (if it exists).

    Signed-off-by: "Theodore Ts'o" <>
    Signed-off-by: Jan Kara <>
    Signed-off-by: Greg Kroah-Hartman <>

    fs/jbd/journal.c | 16 +++++++++++++---
    1 file changed, 13 insertions(+), 3 deletions(-)

    --- a/fs/jbd/journal.c
    +++ b/fs/jbd/journal.c
    @@ -435,9 +435,12 @@ int __log_space_left(journal_t *journal)
    int __log_start_commit(journal_t *journal, tid_t target)
    - * Are we already doing a recent enough commit?
    + * The only transaction we can possibly wait upon is the
    + * currently running transaction (if it exists). Otherwise,
    + * the target tid must be an old one.
    - if (!tid_geq(journal->j_commit_request, target)) {
    + if (journal->j_running_transaction &&
    + journal->j_running_transaction->t_tid == target) {
    * We want a new commit: OK, mark the request and wakup the
    * commit thread. We do _not_ do the commit ourselves.
    @@ -449,7 +452,14 @@ int __log_start_commit(journal_t *journa
    return 1;
    - }
    + } else if (!tid_geq(journal->j_commit_request, target))
    + /* This should never happen, but if it does, preserve
    + the evidence before kjournald goes into a loop and
    + increments j_commit_sequence beyond all recognition. */
    + WARN_ONCE(1, "jbd: bad log_start_commit: %u %u %u %u\n",
    + journal->j_commit_request, journal->j_commit_sequence,
    + target, journal->j_running_transaction ?
    + journal->j_running_transaction->t_tid : 0);
    return 0;

     \ /
      Last update: 2011-06-16 09:31    [W:0.022 / U:29.504 seconds]
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