linux-kernel - Re: [PATCH] padata: Replace delayed timer with immediate workqueue in padata

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Message-ID: <20190719142735.s2oggziz4wqwebxf@ca-dmjordan1.us.oracle.com>
Date:   Fri, 19 Jul 2019 10:27:35 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arch@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH] padata: Replace delayed timer with immediate workqueue
 in padata_reorder

On Thu, Jul 18, 2019 at 10:56:34PM +0800, Herbert Xu wrote:
> On Thu, Jul 18, 2019 at 10:27:30AM -0400, Daniel Jordan wrote:
> >
> > That's what I expected when I first saw it too, but nr_cpumask_bits is returned
> > to signal the end of the iteration.  The patch always passes 0 for the 'start'
> > argument, so when cpumask_next_wrap is called with the last cpu in the mask,
> > the end-of-iteration case is triggered.  To reassure you and myself :) I ran it
> > and got the expected crash.
> > 
> > Passing pd->cpu for the start argument instead avoids that problem, but the
> > one-cpu-in-mask case still needs handling because cpumask_next_wrap always
> > signals end of iteration for that, hence the cpumask_weight check.
> 
> My bad.  I should have set start to -1 to make it do the right thing.

Oh, you're right, that's nicer, just noticed other callers do it that way as
well.