linux-kernel - Re: [PATCH 1/9] crypto: engine: workqueue can only be processed one by one

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Date:   Tue, 28 Jan 2020 17:55:34 +0100
From:   Corentin Labbe <clabbe.montjoie@...il.com>
To:     Horia Geanta <horia.geanta@....com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "mripard@...nel.org" <mripard@...nel.org>,
        "wens@...e.org" <wens@...e.org>,
        Iuliana Prodan <iuliana.prodan@....com>,
        "linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] crypto: engine: workqueue can only be processed one
 by one

On Tue, Jan 28, 2020 at 04:58:00PM +0100, Corentin Labbe wrote:
> On Tue, Jan 28, 2020 at 03:50:14PM +0000, Horia Geanta wrote:
> > On 1/22/2020 12:46 PM, Corentin Labbe wrote:
> > > Some bykeshedding are unnecessary since a workqueue can only be executed
> > > one by one.
> > > This behaviour is documented in:
> > > - kernel/kthread.c: comment of kthread_worker_fn()
> > > - Documentation/core-api/workqueue.rst: the functions associated with the work items one after the other
> > [...]
> > > @@ -73,16 +73,6 @@ static void crypto_pump_requests(struct crypto_engine *engine,
> > >  
> > >  	spin_lock_irqsave(&engine->queue_lock, flags);
> > >  
> > > -	/* Make sure we are not already running a request */
> > > -	if (engine->cur_req)
> > > -		goto out;
> > > -
> > This check is here for a good reason, namely because crypto engine
> > cannot currently handle multiple crypto requests being in "flight"
> > in parallel.
> > 
> > More exactly, if this check is removed the following sequence could occur:
> > crypto_pump_work() -> crypto_pump_requests() -> .do_one_request(areq1)
> > crypto_pump_work() -> crypto_pump_requests() -> .do_one_request(areq2)
> > crypto_finalize_request(areq1)
> > crypto_finalize_request(areq2)
> > 
> 
> As explained in the commitlog, crypto_pump_work() cannot be ran twice.
> 

Sorry, I have misunderstood and wrongly answered.

Right since some driver does not block on do_one_request(), crypto_pump_work() can be ran one after one and so launch two request.

So this patch is bad.

Regards