linux-kernel - Re: [PATCH 3/2] padata: initialize usable masks to reflect offlined CPU

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Message-ID: <20190822035143.GB32551@gondor.apana.org.au>
Date:   Thu, 22 Aug 2019 13:51:43 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/2] padata: initialize usable masks to reflect offlined
 CPU

On Mon, Aug 12, 2019 at 05:02:00PM -0400, Daniel Jordan wrote:
> __padata_remove_cpu clears the offlined CPU from the usable masks after
> padata_alloc_pd has initialized pd->cpu, which means pd->cpu could be
> initialized to this CPU, causing padata to wait indefinitely for the
> next job in padata_get_next.
> 
> Make the usable masks reflect the offline CPU when they're established
> in padata_setup_cpumasks so pd->cpu is initialized properly.
> 
> Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: linux-crypto@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---
> 
> Hi, one more edge case.  All combinations of CPUs among
> parallel_cpumask, serial_cpumask, and CPU hotplug have now been tested
> in a 4-CPU VM, and an 8-CPU VM has run with random combinations of these
> settings for over an hour.
> 
>  kernel/padata.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)

If we modify patch 2/2 by calling this after cpu_online_mask
has been updated then this problem should go away because we
can then remove the cpumask_clear_cpu calls.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt