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Date:   Mon, 20 Jun 2022 14:46:55 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>
CC:     "Williams, Dan J" <dan.j.williams@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        "Lukas Wunner" <lukas@wunner.de>,
        Davidlohr Bueso <dave@stgolabs.net>,
        "Schofield, Alison" <alison.schofield@intel.com>,
        "Verma, Vishal L" <vishal.l.verma@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Ben Widawsky" <ben@bwidawsk.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: [PATCH V10 3/9] PCI: Create PCI library functions in support of
 DOE mailboxes.
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On Mon, Jun 20, 2022 at 01:39:45AM -0700, Zhuo, Qiuxu wrote:
> > From: ira.weiny@intel.com <ira.weiny@intel.com>
> > Sent: Sunday, June 5, 2022 8:51 AM
> > ...
> > +static void retire_cur_task(struct pci_doe_mb *doe_mb) {
> > +	spin_lock(&doe_mb->task_lock);
> > +	doe_mb->cur_task = NULL;
> > +	spin_unlock(&doe_mb->task_lock);
> > +	wake_up_interruptible(&doe_mb->wq);
> > +}
> > +
> > +static void doe_statemachine_work(struct work_struct *work) {
> > +	struct delayed_work *w = to_delayed_work(work);
> > +	struct pci_doe_mb *doe_mb = container_of(w, struct pci_doe_mb,
> > +						 statemachine);
> > +	struct pci_dev *pdev = doe_mb->pdev;
> > +	int offset = doe_mb->cap_offset;
> > +	enum pci_doe_state prev_state;
> > +	struct pci_doe_task *task;
> > +	u32 val;
> > +	int rc;
> > +
> > +	spin_lock(&doe_mb->task_lock);
> > +	task = doe_mb->cur_task;
> > +	spin_unlock(&doe_mb->task_lock);
> 
>               I don't think it needs the lock protection here. 
>               No matter "task" is !NULL or NULL, it is checked before it's used within this function.

No it does not.

However, Dan has suggested reworking the workqueue and I think it will
eliminate this.  I kept the lock more as a marker of where cur_task was being
used even though it was not required.  The fact that the rest of the function
goes on to use a local alias was suspicious but was covered by the workqueue
operation.  I tried to explain that in the commit message but reworking as Dan
has suggested is better overall.

Thanks for the review!

Ira