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

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Date: Thu, 13 Jun 2024 13:38:24 -0700
From: "Nelson, Shannon" <shannon.nelson@....com>
To: 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 6/12/2024 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