Re: [PATCH V3 2/2] PCI/DOE: Remove asynchronous task support

[Ira Weiny <ira.weiny@intel.com>]

On Mon, Nov 28, 2022 at 09:58:11AM -0800, Alison Schofield wrote:
> 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

Ok yes this makes sense.

Thanks for looking!
Ira

> 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
> >