Re: [PATCH] jbd: abort instead of waiting for nonexistent transactions

Andrew Morton
2008-08-05T00:04:11Z

On Tue, 5 Aug 2008 00:51:34 +0100 "Duane Griffin" <duaneg@dghda.com> wrote:

> The __log_wait_for_space function sits in a loop checkpointing transactions
> until there is sufficient space free in the journal. However, if there are
> no transactions to be processed (e.g. because the free space calculation is
> wrong due to a corrupted filesystem) it will never progress.
>
> Check for space being required when no transactions are outstanding and
> abort the journal instead of endlessly looping.
>
> This patch fixes the bug reported by Sami Liedes at:
> http://bugzilla.kernel.org/show_bug.cgi?id=10976
>
> Signed-off-by: Duane Griffin <duaneg@dghda.com>
> Tested-by: Sami Liedes <sliedes@cc.hut.fi>
> ---
> diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
> index a5432bb..9fac177 100644
> --- a/fs/jbd/checkpoint.c
> +++ b/fs/jbd/checkpoint.c
> @@ -126,14 +126,29 @@ void __log_wait_for_space(journal_t *journal)
>
> /*
> * Test again, another process may have checkpointed while we
> - * were waiting for the checkpoint lock
> + * were waiting for the checkpoint lock. If there are no
> + * outstanding transactions there is nothing to checkpoint and
> + * we can't make progress. Abort the journal in this case.
> */
> spin_lock(&journal->j_state_lock);
> + spin_lock(&journal->j_list_lock);
> nblocks = jbd_space_needed(journal);
> if (__log_space_left(journal) < nblocks) {
> + int chkpt = journal->j_checkpoint_transactions != NULL;
> +
> + spin_unlock(&journal->j_list_lock);
> spin_unlock(&journal->j_state_lock);
> - log_do_checkpoint(journal);
> + if (chkpt) {
> + log_do_checkpoint(journal);
> + } else {
> + printk(KERN_ERR "%s: no transactions\n",
> + __func__);
> + journal_abort(journal, 0);
> + }
> +
> spin_lock(&journal->j_state_lock);
> + } else {
> + spin_unlock(&journal->j_list_lock);
> }
> mutex_unlock(&journal->j_checkpoint_mutex);
> }

I don't expect that the additional taking of j_list_lock in here does
anything useful.

Plus.. after j_list_lock has been dropped, new transactions could
theoretically appear at journal->j_checkpoint_transactions, so we
_could_ reclaim more journal space. But a) that probably couldn't
happen due to ->j_state_lock and lots of other things and b) it's
hopelessly theoretical even if it _could_ happen, methinks. Just
sayin'..