linux-kernel - Re: [PATCH V2 1/2] PCI/DOE: Remove the pci_doe_flush

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Date:   Tue, 22 Nov 2022 16:34:26 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lukas Wunner <lukas@...ner.de>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Gregory Price <gregory.price@...verge.com>,
        "Li, Ming" <ming4.li@...el.com>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] PCI/DOE: Remove the pci_doe_flush_mb() call

On Tue, 22 Nov 2022 07:53:23 -0800
ira.weiny@...el.com wrote:

> From: Ira Weiny <ira.weiny@...el.com>
> 
> 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.
> 
> For these reasons, pci_doe_flush_mb() will never be called while tasks
> are being processed and there is no use for it.
> 
> Remove the dead code around pci_doe_flush_mb().
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Looks fine I think, though one question inline.
 
> ---
>  drivers/pci/doe.c | 48 ++++-------------------------------------------
>  1 file changed, 4 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> index e402f05068a5..260313e9052e 100644
> --- a/drivers/pci/doe.c
> +++ b/drivers/pci/doe.c
> @@ -24,10 +24,9 @@
>  
>  /* Timeout of 1 second from 6.30.2 Operation, PCI Spec r6.0 */
>  #define PCI_DOE_TIMEOUT HZ
> -#define PCI_DOE_POLL_INTERVAL	(PCI_DOE_TIMEOUT / 128)
> +#define PCI_DOE_POLL_INTERVAL	8

Why this change?  

>  
> -#define PCI_DOE_FLAG_CANCEL	0
> -#define PCI_DOE_FLAG_DEAD	1
> +#define PCI_DOE_FLAG_DEAD	0
>  
>  /**
>   * struct pci_doe_mb - State for a single DOE mailbox
> @@ -53,15 +52,6 @@ struct pci_doe_mb {
>  	unsigned long flags;
>  };
>  
> -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 +72,9 @@ 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);
>  		pci_read_config_dword(pdev, offset + PCI_DOE_STATUS, &val);
>  
>  		/* Abort success! */
> @@ -278,11 +265,7 @@ 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);
>  		goto retry_resp;
>  	}
>  
> @@ -383,21 +366,6 @@ 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 +418,6 @@ 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",