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Date:   Mon, 28 Nov 2022 09:58:11 -0800
From:   Alison Schofield <alison.schofield@intel.com>
To:     ira.weiny@intel.com
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Gregory Price <gregory.price@memverge.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        "Li, Ming" <ming4.li@intel.com>, Lukas Wunner <lukas@wunner.de>,
        Vishal Verma <vishal.l.verma@intel.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-cxl@vger.kernel.org
Subject: Re: [PATCH V3 2/2] PCI/DOE: Remove asynchronous task support
Message-ID: <Y4T2s7u8Z8m9q2oS@aschofie-mobl2>
References: <20221128040338.1936529-1-ira.weiny@intel.com>
 <20221128040338.1936529-3-ira.weiny@intel.com>
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On Sun, Nov 27, 2022 at 08:03:38PM -0800, Ira Weiny wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> Gregory Price and Jonathan Cameron reported a bug within
> pci_doe_submit_task().[1]  The issue was that work item initialization
> needs to be done with either INIT_WORK_ONSTACK() or INIT_WORK()
> depending on how the work item is allocated.
> 
> Initially, it was anticipated that DOE tasks were going to need to be
> submitted asynchronously and the code was designed thusly.  Many
> alternatives were discussed to fix the work initialization issue.[2]
> 
> However, all current users submit tasks synchronously and this has
> therefore become an unneeded maintenance burden.  Remove the extra
> maintenance burden by replacing asynchronous task submission with
> a synchronous wait function.[3]

Commit msg: Please look at replacing this:
PCI/DOE: Remove asynchronous task support
with something like this:
PCI/DOE: Replace async task submission with sync wait function
to more accurately reflect what this patch does. It is not
only removing code.

Like the first patch, I'm unfamiliar w the details, and am
just expecting that a patch that says 'Remove' doesn't add
anything.

> 
> [1] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m88a7f50dcce52f30c8bf5c3dcc06fa9843b54a2d
> [2] https://lore.kernel.org/linux-cxl/Y3kSDQDur+IUDs2O@iweiny-mobl/T/#m0f057773d9c75432fcfcc54a2604483fe82abe92
> [3] https://lore.kernel.org/linux-cxl/Y3kSDQDur+IUDs2O@iweiny-mobl/T/#m32d3f9b208ef7486bc148d94a326b26b2d3e69ff
> 
> Reported-by: Gregory Price <gregory.price@memverge.com>
> Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Suggested-by: "Li, Ming" <ming4.li@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
> ---
> Changes from V2:
> 	Jonathan
> 		Fix comment on struct pci_doe_mb
> 		Remove signal_task_complete()
> 
> Changes from V1:
> 	Dan Williams:
> 		Use mutex_lock_interruptible()
> 		Adjust comment to lock the doe_mb structure not the
> 		code
> 	Adjust the locking based on the new series which eliminated
> 	PCI_DOE_FLAG_CANCEL.
> 
> Thanks to Dan for the bulk of the patch.
> Thanks to Ming for pointing out the need for a lock to prevent more
> than 1 task from being processed at a time.
> ---
>  drivers/cxl/core/pci.c  | 16 ++------
>  drivers/pci/doe.c       | 86 +++++++++++++----------------------------
>  include/linux/pci-doe.h | 11 +-----
>  3 files changed, 31 insertions(+), 82 deletions(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 9240df53ed87..58977e0712b6 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -490,21 +490,14 @@ static struct pci_doe_mb *find_cdat_doe(struct device *uport)
>  		    CXL_DOE_TABLE_ACCESS_TABLE_TYPE_CDATA) |		\
>  	 FIELD_PREP(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, (entry_handle)))
>  
> -static void cxl_doe_task_complete(struct pci_doe_task *task)
> -{
> -	complete(task->private);
> -}
> -
>  struct cdat_doe_task {
>  	u32 request_pl;
>  	u32 response_pl[32];
> -	struct completion c;
>  	struct pci_doe_task task;
>  };
>  
>  #define DECLARE_CDAT_DOE_TASK(req, cdt)                       \
>  struct cdat_doe_task cdt = {                                  \
> -	.c = COMPLETION_INITIALIZER_ONSTACK(cdt.c),           \
>  	.request_pl = req,				      \
>  	.task = {                                             \
>  		.prot.vid = PCI_DVSEC_VENDOR_ID_CXL,        \
> @@ -513,8 +506,6 @@ struct cdat_doe_task cdt = {                                  \
>  		.request_pl_sz = sizeof(cdt.request_pl),      \
>  		.response_pl = cdt.response_pl,               \
>  		.response_pl_sz = sizeof(cdt.response_pl),    \
> -		.complete = cxl_doe_task_complete,            \
> -		.private = &cdt.c,                            \
>  	}                                                     \
>  }
>  
> @@ -525,12 +516,12 @@ static int cxl_cdat_get_length(struct device *dev,
>  	DECLARE_CDAT_DOE_TASK(CDAT_DOE_REQ(0), t);
>  	int rc;
>  
> -	rc = pci_doe_submit_task(cdat_doe, &t.task);
> +	rc = pci_doe_submit_task_wait(cdat_doe, &t.task);
>  	if (rc < 0) {
>  		dev_err(dev, "DOE submit failed: %d", rc);
>  		return rc;
>  	}
> -	wait_for_completion(&t.c);
> +
>  	if (t.task.rv < sizeof(u32))
>  		return -EIO;
>  
> @@ -554,12 +545,11 @@ static int cxl_cdat_read_table(struct device *dev,
>  		u32 *entry;
>  		int rc;
>  
> -		rc = pci_doe_submit_task(cdat_doe, &t.task);
> +		rc = pci_doe_submit_task_wait(cdat_doe, &t.task);
>  		if (rc < 0) {
>  			dev_err(dev, "DOE submit failed: %d", rc);
>  			return rc;
>  		}
> -		wait_for_completion(&t.c);
>  		/* 1 DW header + 1 DW data min */
>  		if (t.task.rv < (2 * sizeof(u32)))
>  			return -EIO;
> diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> index 685e7d26c7eb..b399f0f4fb5d 100644
> --- a/drivers/pci/doe.c
> +++ b/drivers/pci/doe.c
> @@ -18,7 +18,6 @@
>  #include <linux/mutex.h>
>  #include <linux/pci.h>
>  #include <linux/pci-doe.h>
> -#include <linux/workqueue.h>
>  
>  #define PCI_DOE_PROTOCOL_DISCOVERY 0
>  
> @@ -40,7 +39,7 @@
>   * @cap_offset: Capability offset
>   * @prots: Array of protocols supported (encoded as long values)
>   * @wq: Wait queue for work item
> - * @work_queue: Queue of pci_doe_work items
> + * @lock: Lock state of doe_mb during task processing
>   * @flags: Bit array of PCI_DOE_FLAG_* flags
>   */
>  struct pci_doe_mb {
> @@ -49,7 +48,7 @@ struct pci_doe_mb {
>  	struct xarray prots;
>  
>  	wait_queue_head_t wq;
> -	struct workqueue_struct *work_queue;
> +	struct mutex lock;
>  	unsigned long flags;
>  };
>  
> @@ -196,12 +195,6 @@ static int pci_doe_recv_resp(struct pci_doe_mb *doe_mb, struct pci_doe_task *tas
>  	return min(length, task->response_pl_sz / sizeof(u32)) * sizeof(u32);
>  }
>  
> -static void signal_task_complete(struct pci_doe_task *task, int rv)
> -{
> -	task->rv = rv;
> -	task->complete(task);
> -}
> -
>  static void signal_task_abort(struct pci_doe_task *task, int rv)
>  {
>  	struct pci_doe_mb *doe_mb = task->doe_mb;
> @@ -216,13 +209,11 @@ static void signal_task_abort(struct pci_doe_task *task, int rv)
>  			doe_mb->cap_offset);
>  		set_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags);
>  	}
> -	signal_task_complete(task, rv);
> +	task->rv = rv;
>  }
>  
> -static void doe_statemachine_work(struct work_struct *work)
> +static void exec_task(struct pci_doe_task *task)
>  {
> -	struct pci_doe_task *task = container_of(work, struct pci_doe_task,
> -						 work);
>  	struct pci_doe_mb *doe_mb = task->doe_mb;
>  	struct pci_dev *pdev = doe_mb->pdev;
>  	int offset = doe_mb->cap_offset;
> @@ -231,7 +222,7 @@ static void doe_statemachine_work(struct work_struct *work)
>  	int rc;
>  
>  	if (test_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags)) {
> -		signal_task_complete(task, -EIO);
> +		task->rv = -EIO;
>  		return;
>  	}
>  
> @@ -276,12 +267,7 @@ static void doe_statemachine_work(struct work_struct *work)
>  		return;
>  	}
>  
> -	signal_task_complete(task, rc);
> -}
> -
> -static void pci_doe_task_complete(struct pci_doe_task *task)
> -{
> -	complete(task->private);
> +	task->rv = rc;
>  }
>  
>  static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
> @@ -290,7 +276,6 @@ static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
>  	u32 request_pl = FIELD_PREP(PCI_DOE_DATA_OBJECT_DISC_REQ_3_INDEX,
>  				    *index);
>  	u32 response_pl;
> -	DECLARE_COMPLETION_ONSTACK(c);
>  	struct pci_doe_task task = {
>  		.prot.vid = PCI_VENDOR_ID_PCI_SIG,
>  		.prot.type = PCI_DOE_PROTOCOL_DISCOVERY,
> @@ -298,17 +283,13 @@ static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
>  		.request_pl_sz = sizeof(request_pl),
>  		.response_pl = &response_pl,
>  		.response_pl_sz = sizeof(response_pl),
> -		.complete = pci_doe_task_complete,
> -		.private = &c,
>  	};
>  	int rc;
>  
> -	rc = pci_doe_submit_task(doe_mb, &task);
> +	rc = pci_doe_submit_task_wait(doe_mb, &task);
>  	if (rc < 0)
>  		return rc;
>  
> -	wait_for_completion(&c);
> -
>  	if (task.rv != sizeof(response_pl))
>  		return -EIO;
>  
> @@ -360,13 +341,6 @@ static void pci_doe_xa_destroy(void *mb)
>  	xa_destroy(&doe_mb->prots);
>  }
>  
> -static void pci_doe_destroy_workqueue(void *mb)
> -{
> -	struct pci_doe_mb *doe_mb = mb;
> -
> -	destroy_workqueue(doe_mb->work_queue);
> -}
> -
>  /**
>   * pcim_doe_create_mb() - Create a DOE mailbox object
>   *
> @@ -392,25 +366,13 @@ struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset)
>  	doe_mb->pdev = pdev;
>  	doe_mb->cap_offset = cap_offset;
>  	init_waitqueue_head(&doe_mb->wq);
> +	mutex_init(&doe_mb->lock);
>  
>  	xa_init(&doe_mb->prots);
>  	rc = devm_add_action(dev, pci_doe_xa_destroy, doe_mb);
>  	if (rc)
>  		return ERR_PTR(rc);
>  
> -	doe_mb->work_queue = alloc_ordered_workqueue("%s %s DOE [%x]", 0,
> -						dev_driver_string(&pdev->dev),
> -						pci_name(pdev),
> -						doe_mb->cap_offset);
> -	if (!doe_mb->work_queue) {
> -		pci_err(pdev, "[%x] failed to allocate work queue\n",
> -			doe_mb->cap_offset);
> -		return ERR_PTR(-ENOMEM);
> -	}
> -	rc = devm_add_action_or_reset(dev, pci_doe_destroy_workqueue, doe_mb);
> -	if (rc)
> -		return ERR_PTR(rc);
> -
>  	/* Reset the mailbox by issuing an abort */
>  	rc = pci_doe_abort(doe_mb);
>  	if (rc) {
> @@ -457,24 +419,25 @@ bool pci_doe_supports_prot(struct pci_doe_mb *doe_mb, u16 vid, u8 type)
>  EXPORT_SYMBOL_GPL(pci_doe_supports_prot);
>  
>  /**
> - * pci_doe_submit_task() - Submit a task to be processed by the state machine
> + * pci_doe_submit_task_wait() - Submit and execute a task
>   *
>   * @doe_mb: DOE mailbox capability to submit to
> - * @task: task to be queued
> - *
> - * Submit a DOE task (request/response) to the DOE mailbox to be processed.
> - * Returns upon queueing the task object.  If the queue is full this function
> - * will sleep until there is room in the queue.
> + * @task: task to be run
>   *
> - * task->complete will be called when the state machine is done processing this
> - * task.
> + * Submit and run DOE task (request/response) to the DOE mailbox to be
> + * processed.
>   *
>   * Excess data will be discarded.
>   *
> - * RETURNS: 0 when task has been successfully queued, -ERRNO on error
> + * Context: non-interrupt
> + *
> + * RETURNS: 0 when task was executed, the @task->rv holds the status
> + * result of the executed opertion, -ERRNO on failure to submit.
>   */
> -int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> +int pci_doe_submit_task_wait(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
>  {
> +	int rc;
> +
>  	if (!pci_doe_supports_prot(doe_mb, task->prot.vid, task->prot.type))
>  		return -EINVAL;
>  
> @@ -490,8 +453,13 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
>  		return -EIO;
>  
>  	task->doe_mb = doe_mb;
> -	INIT_WORK(&task->work, doe_statemachine_work);
> -	queue_work(doe_mb->work_queue, &task->work);
> +
> +	rc = mutex_lock_interruptible(&doe_mb->lock);
> +	if (rc)
> +		return rc;
> +	exec_task(task);
> +	mutex_unlock(&doe_mb->lock);
> +
>  	return 0;
>  }
> -EXPORT_SYMBOL_GPL(pci_doe_submit_task);
> +EXPORT_SYMBOL_GPL(pci_doe_submit_task_wait);
> diff --git a/include/linux/pci-doe.h b/include/linux/pci-doe.h
> index ed9b4df792b8..55e6e45b87f3 100644
> --- a/include/linux/pci-doe.h
> +++ b/include/linux/pci-doe.h
> @@ -29,9 +29,6 @@ struct pci_doe_mb;
>   * @response_pl: The response payload
>   * @response_pl_sz: Size of the response payload (bytes)
>   * @rv: Return value.  Length of received response or error (bytes)
> - * @complete: Called when task is complete
> - * @private: Private data for the consumer
> - * @work: Used internally by the mailbox
>   * @doe_mb: Used internally by the mailbox
>   *
>   * The payload sizes and rv are specified in bytes with the following
> @@ -50,11 +47,6 @@ struct pci_doe_task {
>  	u32 *response_pl;
>  	size_t response_pl_sz;
>  	int rv;
> -	void (*complete)(struct pci_doe_task *task);
> -	void *private;
> -
> -	/* No need for the user to initialize these fields */
> -	struct work_struct work;
>  	struct pci_doe_mb *doe_mb;
>  };
>  
> @@ -72,6 +64,5 @@ struct pci_doe_task {
>  
>  struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset);
>  bool pci_doe_supports_prot(struct pci_doe_mb *doe_mb, u16 vid, u8 type);
> -int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task);
> -
> +int pci_doe_submit_task_wait(struct pci_doe_mb *doe_mb, struct pci_doe_task *task);
>  #endif
> -- 
> 2.37.2
>