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    Subject[ 059/171] jbd2: fix assertion failure in jbd2_journal_flush()
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jan Kara <jack@suse.cz>

    commit d7961c7fa4d2e3c3f12be67e21ba8799b5a7238a upstream.

    The following race is possible between start_this_handle() and someone
    calling jbd2_journal_flush().

    Process A Process B
    start_this_handle().
    if (journal->j_barrier_count) # false
    if (!journal->j_running_transaction) { #true
    read_unlock(&journal->j_state_lock);
    jbd2_journal_lock_updates()
    jbd2_journal_flush()
    write_lock(&journal->j_state_lock);
    if (journal->j_running_transaction) {
    # false
    ... wait for committing trans ...
    write_unlock(&journal->j_state_lock);
    ...
    write_lock(&journal->j_state_lock);
    if (!journal->j_running_transaction) { # true
    jbd2_get_transaction(journal, new_transaction);
    write_unlock(&journal->j_state_lock);
    goto repeat; # eventually blocks on j_barrier_count > 0
    ...
    J_ASSERT(!journal->j_running_transaction);
    # fails

    We fix the race by rechecking j_barrier_count after reacquiring j_state_lock
    in exclusive mode.

    Reported-by: yjwsignal@empal.com
    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/jbd2/transaction.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/fs/jbd2/transaction.c
    +++ b/fs/jbd2/transaction.c
    @@ -209,7 +209,8 @@ repeat:
    if (!new_transaction)
    goto alloc_transaction;
    write_lock(&journal->j_state_lock);
    - if (!journal->j_running_transaction) {
    + if (!journal->j_running_transaction &&
    + !journal->j_barrier_count) {
    jbd2_get_transaction(journal, new_transaction);
    new_transaction = NULL;
    }



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