On Mon, 7 Nov 2011 18:29:39 +0100, Jan Kara <jack@xxxxxxx> wrote:
> On Mon 07-11-11 12:00:41, Dmitry Monakhov wrote:
> > On Fri, 28 Oct 2011 14:34:31 +0900, Kazuya Mio <k-mio@xxxxxxxxxxxxx> wrote:
> > > 2011/10/25 22:40, Jan Kara wrote:
> > > > Please no. Generally this boils down to what do we do with dirty data
> > > > when there's error in writing them out. Currently we just throw them away
> > > > (e.g. in media error case) but I don't think that's a generally good thing
> > > > because e.g. admin may want to copy the data to other working storage or
> > > > so. So I think we should rather keep the data and provide a mechanism for
> > > > userspace to ask kernel to get rid of the data (so that we don't eventually
> > > > run OOM).
> > >
> > > I see. I agree with you.
> > >
> > > >> Do you have any ideas?
> > > > So the question is what would you like to achieve. If you just want to
> > > > unblock a thread then a solution would be to make a thread at
> > > > balance_dirty_pages() killable. If generally you want to get rid of dirty
> > > > memory, then I don't have a really good answer but throwing dirty data away
> > > > seems like a bad answer to me.
> > >
> > > The problem is that we cannot unmount the corrupted filesystem due to
> > > un-killable dd process. We must bring down the system to resume the service
> > > with no dirty pages. I think it is important for the service continuity
> > > to be able to kill the thread handling in balance_dirty_pages().
> > In fact you are very lucky because dd is just deadlocked, in many cases
> > journal abort result in BUG_ON triggering(if IO load is high enough).
> Can you provide the exact kernel message? I'd be interested...
Several times i've failed in journal_stop() here:
int jbd2_journal_stop(handle_t *handle)
{
transaction_t *transaction = handle->h_transaction;
journal_t *journal = transaction->t_journal;
int err, wait_for_commit = 0;
tid_t tid;
pid_t pid;
J_ASSERT(journal_current_handle() == handle);
if (is_handle_aborted(handle))
err = -EIO;
else {
J_ASSERT(atomic_read(&transaction->t_updates) > 0);
##FAILED HERE ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
err = 0;
}
>
> > This is because transaction abort check is racy. Right now i've no good
> > fix which has reasonable performance. My latest idea is to protect
> > transaction abort check via SRCU.
> Yeah, the code does not seem to care about races too much but I don't see
> which BUG_ON would be triggered...
>
> Honza
> --
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
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