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

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Date:   Fri, 12 Jul 2019 12:10:12 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        <andrea.parri@...rulasolutions.com>, <boqun.feng@...il.com>,
        <paulmck@...ux.ibm.com>, <peterz@...radead.org>,
        <linux-arch@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] padata: use smp_mb in padata_reorder to avoid orphaned
 padata jobs

On Fri, Jul 12, 2019 at 06:06:36PM +0800, Herbert Xu wrote:
> Daniel Jordan <daniel.m.jordan@...cle.com> wrote:
> >
> > CPU0                                 CPU1
> > 
> > padata_reorder                       padata_do_serial
> >  LOAD reorder_objects  // 0
> >                                       INC reorder_objects  // 1
> >                                       padata_reorder
> >                                         TRYLOCK pd->lock   // failed
> >  UNLOCK pd->lock
> 
> I think this can't happen because CPU1 won't call padata_reorder
> at all as it's the wrong CPU so it gets pushed back onto a work
> queue which will go back to CPU0.
> 
> Steffen, could you please take a look at this as there clearly
> is a problem here?

I'm currently travelling, will have a look at it when I'm back.