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

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Message-ID: <Y4T1M7vAuHdMcNiy@aschofie-mobl2>
Date:   Mon, 28 Nov 2022 09:51:47 -0800
From:   Alison Schofield <alison.schofield@...el.com>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lukas Wunner <lukas@...ner.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.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 V3 1/2] PCI/DOE: Remove the pci_doe_flush_mb() call

On Sun, Nov 27, 2022 at 08:03:37PM -0800, Ira Weiny 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().

The commit message says "Remove ...." and the commit log only
talks about removing code, yet an msleep() is added.
Can those be clearer?

> 
> Cc: Lukas Wunner <lukas@...ner.de>
> Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from V2:
> 	Lukas
> 		Clarify commit message.
> 	Jonathan
> 		Add comment for changed poll interval.
> ---
>  drivers/pci/doe.c | 49 +++++------------------------------------------
>  1 file changed, 5 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> index e402f05068a5..685e7d26c7eb 100644
> --- a/drivers/pci/doe.c
> +++ b/drivers/pci/doe.c
> @@ -24,10 +24,10 @@
>  
>  /* 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)
> +/* Interval to poll mailbox status */
> +#define PCI_DOE_POLL_INTERVAL_MSECS	8
>  
> -#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 +53,6 @@ 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 +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);
>  
>  		/* 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;
>  	}
>  
> @@ -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",
> -- 
> 2.37.2
>