linux-kernel - Re: [PATCH V3 1/2] PCI/DOE: Remove the pci_doe_flush

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Date:   Mon, 28 Nov 2022 13:51:24 +0800
From:   "Li, Ming" <ming4.li@...el.com>
To:     <ira.weiny@...el.com>
CC:     Lukas Wunner <lukas@...ner.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Gregory Price <gregory.price@...verge.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-cxl@...r.kernel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH V3 1/2] PCI/DOE: Remove the pci_doe_flush_mb() call


On 11/28/2022 12:03 PM, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> pci_doe_flush_mb() does not work and is currently unused.
> 
> It does not work because each struct doe_mb is managed as part of the
> PCI device.  They can't go away as long as the PCI device exists.
> pci_doe_flush_mb() was set up to flush the workqueue and prevent any
> further submissions to the mailboxes when the PCI device goes away.
> Unfortunately, this was fundamentally flawed.  There was no guarantee
> that a struct doe_mb remained after pci_doe_flush_mb() returned.
> Therefore, the doe_mb state could be invalid when those threads waiting
> on the workqueue were flushed.
> 
> Fortunately the current code is safe because all callers make a
> synchronous call to pci_doe_submit_task() and maintain a reference on
> the PCI device.  Therefore pci_doe_flush_mb() is effectively unused.
> 
> Rather than attempt to fix pci_doe_flush_mb() just remove the dead code
> around pci_doe_flush_mb().
> 
> Cc: Lukas Wunner <lukas@...ner.de>
> Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Some comments inline.

> 
> ---
> Changes from V2:
> 	Lukas
> 		Clarify commit message.
> 	Jonathan
> 		Add comment for changed poll interval.

...

>  
> -static int pci_doe_wait(struct pci_doe_mb *doe_mb, unsigned long timeout)
> -{
> -	if (wait_event_timeout(doe_mb->wq,
> -			       test_bit(PCI_DOE_FLAG_CANCEL, &doe_mb->flags),
> -			       timeout))
> -		return -EIO;
> -	return 0;
> -}
> -
>  static void pci_doe_write_ctrl(struct pci_doe_mb *doe_mb, u32 val)
>  {
>  	struct pci_dev *pdev = doe_mb->pdev;
> @@ -82,12 +73,9 @@ static int pci_doe_abort(struct pci_doe_mb *doe_mb)
>  	pci_doe_write_ctrl(doe_mb, PCI_DOE_CTRL_ABORT);
>  
>  	do {
> -		int rc;
>  		u32 val;
>  
> -		rc = pci_doe_wait(doe_mb, PCI_DOE_POLL_INTERVAL);
> -		if (rc)
> -			return rc;
> +		msleep_interruptible(PCI_DOE_POLL_INTERVAL_MSECS);
>  		pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);

Looks like we don't have to use msleep_interruptible() here, can use msleep() directly?

>  
>  		/* Abort success! */
> @@ -278,11 +266,7 @@ static void doe_statemachine_work(struct work_struct *work)
>  			signal_task_abort(task, -EIO);
>  			return;
>  		}
> -		rc = pci_doe_wait(doe_mb, PCI_DOE_POLL_INTERVAL);
> -		if (rc) {
> -			signal_task_abort(task, rc);
> -			return;
> -		}
> +		msleep_interruptible(PCI_DOE_POLL_INTERVAL_MSECS);
>  		goto retry_resp;
>  	}

I guess that you use msleep_interruptible() here for aborting current task when signals come.
So there should be signal_task_abort() and return when msleep_interruptible() receives a signal.

Thanks
Ming

>  
> @@ -383,21 +367,6 @@ static void pci_doe_destroy_workqueue(void *mb)
>  	destroy_workqueue(doe_mb->work_queue);
>  }
>  
> -static void pci_doe_flush_mb(void *mb)
> -{
> -	struct pci_doe_mb *doe_mb = mb;
> -
> -	/* Stop all pending work items from starting */
> -	set_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags);
> -
> -	/* Cancel an in progress work item, if necessary */
> -	set_bit(PCI_DOE_FLAG_CANCEL, &doe_mb->flags);
> -	wake_up(&doe_mb->wq);
> -
> -	/* Flush all work items */
> -	flush_workqueue(doe_mb->work_queue);
> -}
> -
>  /**
>   * pcim_doe_create_mb() - Create a DOE mailbox object
>   *
> @@ -450,14 +419,6 @@ struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset)
>  		return ERR_PTR(rc);
>  	}
>  
> -	/*
> -	 * The state machine and the mailbox should be in sync now;
> -	 * Set up mailbox flush prior to using the mailbox to query protocols.
> -	 */
> -	rc = devm_add_action_or_reset(dev, pci_doe_flush_mb, doe_mb);
> -	if (rc)
> -		return ERR_PTR(rc);
> -
>  	rc = pci_doe_cache_protocols(doe_mb);
>  	if (rc) {
>  		pci_err(pdev, "[%x] failed to cache protocols : %d\n",