linux-kernel - Re: [PATCH 4.19 061/191] padata: always acquire cpu_hotplug

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Date:   Sat, 22 Feb 2020 14:02:50 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Eric Biggers <ebiggers@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        linux-crypto@...r.kernel.org
Subject: Re: [PATCH 4.19 061/191] padata: always acquire cpu_hotplug_lock
 before pinst->lock

On Fri, Feb 21, 2020 at 07:00:45PM -0500, Daniel Jordan wrote:
>On Fri, Feb 21, 2020 at 08:40:34AM +0100, Greg Kroah-Hartman wrote:
>> From: Daniel Jordan <daniel.m.jordan@...cle.com>
>>
>> [ Upstream commit 38228e8848cd7dd86ccb90406af32de0cad24be3 ]
>>
>> lockdep complains when padata's paths to update cpumasks via CPU hotplug
>> and sysfs are both taken:
>>
>>   # echo 0 > /sys/devices/system/cpu/cpu1/online
>>   # echo ff > /sys/kernel/pcrypt/pencrypt/parallel_cpumask
>>
>>   ======================================================
>>   WARNING: possible circular locking dependency detected
>>   5.4.0-rc8-padata-cpuhp-v3+ #1 Not tainted
>>   ------------------------------------------------------
>>   bash/205 is trying to acquire lock:
>>   ffffffff8286bcd0 (cpu_hotplug_lock.rw_sem){++++}, at: padata_set_cpumask+0x2b/0x120
>>
>>   but task is already holding lock:
>>   ffff8880001abfa0 (&pinst->lock){+.+.}, at: padata_set_cpumask+0x26/0x120
>>
>>   which lock already depends on the new lock.
>
>I think this patch should be dropped from all stable queues (4.4, 4.9, 4.14,
>4.19, 5.4, and 5.5).
>
>The main benefit is to un-break lockdep for testing with future padata changes,
>and an actual deadlock seems unlikely.
>
>These stable versions don't fix the ordering in padata_remove_cpu() either
>(nothing calls it though).
>
>I tried the other stable padata patch in this cycle ("padata: validate cpumask
>without removed CPU during offline"), it passed my tests and should stay in.

I've dropped it, thanks.

-- 
Thanks,
Sasha