netdev - Re: [PATCH net-next 4/8] ionic: add work item for missed-doorbell check

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Date: Fri, 14 Jun 2024 03:26:29 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: "Nelson, Shannon" <shannon.nelson@....com>, Jakub Kicinski
	<kuba@...nel.org>
CC: <netdev@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<pabeni@...hat.com>, <brett.creeley@....com>, <drivers@...sando.io>
Subject: Re: [PATCH net-next 4/8] ionic: add work item for missed-doorbell
 check

On 6/13/24 22:38, Nelson, Shannon wrote:
> 
> 
> On 6/12/2024 6:19 PM, Jakub Kicinski wrote:
>> Caution: This message originated from an External Source. Use proper 
>> caution when opening attachments, clicking links, or responding.
>>
>>
>> On Mon, 10 Jun 2024 16:07:02 -0700 Shannon Nelson wrote:
>>> +static void ionic_napi_schedule_do_softirq(struct napi_struct *napi)
>>> +{
>>> +     if (napi_schedule_prep(napi)) {
>>> +             local_bh_disable();
>>> +             __napi_schedule(napi);
>>> +             local_bh_enable();
>>
>> No need to open code napi_schedule()
>>
>>          local_bh_disable();
>>          napi_schedule(napi);
>>          local_bh_enable();
>>
>> is a fairly well-established pattern
> 
> Sure, we can do that.
> 
>>
>>> +     }
>>> +}
>>
>>> +static void ionic_doorbell_check_dwork(struct work_struct *work)
>>> +{
>>> +     struct ionic *ionic = container_of(work, struct ionic,
>>> +                                        doorbell_check_dwork.work);
>>> +     struct ionic_lif *lif = ionic->lif;
>>> +
>>> +     if (test_bit(IONIC_LIF_F_FW_STOPPING, lif->state) ||
>>> +         test_bit(IONIC_LIF_F_FW_RESET, lif->state))
>>> +             return;
>>> +
>>> +     mutex_lock(&lif->queue_lock);
>>
>> This will deadlock under very inopportune circumstances, no?
>>
>> The best way of implementing periodic checks using a workqueue is to
>> only cancel it sync from the .remove callback, before you free the
>> netdev. Otherwise cancel it non-sync or don't cancel at all, and once
>> it takes the lock double check the device is still actually running.
> 
> Hmmm... we'll dig a little more on this.
> 
> Thanks,
> sln

We had a very similar error (with stopping a VF, IIRC); it's easiest to
repro on RT kernels