Re: [PATCH] padata: use smp_mb in padata_reorder to avoid orphaned padata jobs

From: Steffen Klassert
Date: Tue Jul 16 2019 - 07:14:15 EST

On Tue, Jul 16, 2019 at 06:04:47PM +0800, Herbert Xu wrote:
> On Mon, Jul 15, 2019 at 12:10:46PM -0400, Daniel Jordan wrote:
> >
> > I've been wrong before plenty of times, and there's nothing preventing this
> > from being one of those times :) , but in this case I believe what I'm showing
> > is correct.
> >
> > The padata_do_serial call for a given job ensures padata_reorder runs on the
> > CPU that the job hashed to in padata_do_parallel, which is not necessarily the
> > same CPU as the one that padata_do_parallel itself ran on.
> You're right. I was taking the comment in the code at face value,
> never trust comments :)
> While looking at the code in question, I think it is seriously
> broken. For instance, padata_replace does not deal with async
> crypto at all. It would fail miserably if the underlying async
> crypto held onto references to the old pd.

Hm, yes looks like that.

padata_replace should not call padata_free_pd() as long as the
refcount is not zero. Currenlty padata_flush_queues() will
BUG if there are references left.

Maybe we can fix it if we call padata_free_pd() from
padata_serial_worker() when it sent out the last object.