On Wed, Dec 12, 2012 at 04:17:42PM +0100, Jan Kara wrote:
> 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.
>
> CC: [email protected]
> Reported-by:[email protected]
> Signed-off-by: Jan Kara <[email protected]>
Thanks, applied.
- Ted
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