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

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Message-ID: <fc23525a-431f-b714-2384-f707ce50c428@oracle.com>
Date:   Thu, 22 Aug 2019 18:11:38 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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 8/21/19 11:51 PM, Herbert Xu wrote:
> 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.

Yep, agreed.