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

Andrew Morton
2008-08-05T01:42:54Z

On Tue, 5 Aug 2008 02:05:20 +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>
> ---
> diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
> index a5432bb..af2b554 100644
> --- a/fs/jbd/checkpoint.c
> +++ b/fs/jbd/checkpoint.c
> @@ -126,13 +126,24 @@ 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);
> nblocks = jbd_space_needed(journal);
> if (__log_space_left(journal) < nblocks) {
> + int chkpt = journal->j_checkpoint_transactions != NULL;
> +
> 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);
> }
> mutex_unlock(&journal->j_checkpoint_mutex);

umm, OK, but...

There's not really a lot of point in testing
journal->j_checkpoint_transactions inside j_state_lock, is there?
Hence local variable chkpt isn't really needed.

But log_do_checkpoint() already checks to see if there are any
checkpointing transactions upon which to operate, so rather than doing
log_do_checkpoint()'s work for it, perhaps it would be cleaner to teach
log_do_checkpoint() to tell the caller whether it manage to do any
work?

The nice thing about that is that even if
journal->j_checkpoint_transactions is NULL, log_do_checkpoint() might
still be able to do some useful work in cleanup_journal_tail().

otoh, two existing callers of log_do_checkpoint() already test
journal->j_checkpoint_transactions before calling log_do_checkpoint(),
so maybe that's pretty pointless.

otoh2, those existing callers do the seemingly-unneeded
spin_lock(j_list_lock). hrm. So if we're playing match-the-existing
code, we should go with your first patches.

ho hum, I guess I'll do "otoh2".