On 11/19/2022 3:46 AM, Dan Williams wrote: > Ira Weiny wrote: >> On Fri, Nov 18, 2022 at 09:20:38AM +0000, David Laight wrote: >>> From: ira.weiny@xxxxxxxxx >>>> Sent: 18 November 2022 00:05 >>>> >>>> Work item initialization needs to be done with either >>>> INIT_WORK_ONSTACK() or INIT_WORK() depending on how the work item is >>>> allocated. >>>> >>>> The callers of pci_doe_submit_task() allocate struct pci_doe_task on the >>>> stack and pci_doe_submit_task() incorrectly used INIT_WORK(). >>>> >>>> Jonathan suggested creating doe task allocation macros such as >>>> DECLARE_CDAT_DOE_TASK_ONSTACK().[1] The issue with this is the work >>>> function is not known to the callers and must be initialized correctly. >>>> >>>> A follow up suggestion was to have an internal 'pci_doe_work' item >>>> allocated by pci_doe_submit_task().[2] This requires an allocation which >>>> could restrict the context where tasks are used. >>>> >>>> Another idea was to have an intermediate step to initialize the task >>>> struct with a new call.[3] This added a lot of complexity. >>>> >>>> Lukas pointed out that object_is_on_stack() is available to detect this >>>> automatically. >>>> >>>> Use object_is_on_stack() to determine the correct init work function to >>>> call. >>> >>> This is all a bit strange. >>> The 'onstack' flag is needed for the diagnostic check: >>> is_on_stack = object_is_on_stack(addr); >>> if (is_on_stack == onstack) >>> return; >>> pr_warn(...); >>> WARN_ON(1); >>> >> >> :-( >> >>> So setting the flag to the location of the buffer just subverts the check. >>> It that is sane there ought to be a proper way to do it. >> >> Ok this brings me back to my previous point and suggested patch.[*] The >> fundamental bug is that the work item is allocated in different code from >> the code which uses it. Separating the work item from the task. >> >> [*] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@xxxxxxxxxx/T/#m63c636c5135f304480370924f4d03c00357be667 >> >> Bjorn would this solution be acceptable and just use GFP_KERNEL and mark the >> required context for pci_doe_submit_task()? > > It is a waste to have an allocation when one is not needed. The value of > having INIT_WORK_ONSTACK and DECLARE_COMPLETION_ONSTACK is to be clear > at the call site that an async context cares about this stack frame not > going out of scope. > > However, coming full circle, we have zero async users today, and having > the completion and work struct in the task are causing a maintenance > burden. So let's just rip it out for now with something like the > following and circle back to add async support later when it becomes > necessary: (only compile tested) > > > diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c > index 0dbbe8d39b07..69873cdcc911 100644 > --- a/drivers/cxl/core/pci.c > +++ b/drivers/cxl/core/pci.c > @@ -488,21 +488,14 @@ 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, \ > @@ -511,8 +504,6 @@ 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, \ > } \ > } > > @@ -523,12 +514,12 @@ 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; > > @@ -552,12 +543,11 @@ 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 e402f05068a5..115a8ff14afc 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 +39,6 @@ > * @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 > * @flags: Bit array of PCI_DOE_FLAG_* flags > */ > struct pci_doe_mb { > @@ -49,7 +47,6 @@ struct pci_doe_mb { > struct xarray prots; > > wait_queue_head_t wq; > - struct workqueue_struct *work_queue; > unsigned long flags; > }; > > @@ -211,7 +208,6 @@ static int pci_doe_recv_resp(struct pci_doe_mb *doe_mb, struct pci_doe_task *tas > 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) > @@ -231,10 +227,9 @@ static void signal_task_abort(struct pci_doe_task *task, int rv) > signal_task_complete(task, 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; > @@ -295,18 +290,12 @@ static void doe_statemachine_work(struct work_struct *work) > signal_task_complete(task, rc); > } > > -static void pci_doe_task_complete(struct pci_doe_task *task) > -{ > - complete(task->private); > -} > - > static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid, > u8 *protocol) > { > 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, > @@ -314,17 +303,13 @@ 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; > > @@ -376,13 +361,6 @@ 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); > -} > - > static void pci_doe_flush_mb(void *mb) > { > struct pci_doe_mb *doe_mb = mb; > @@ -393,9 +371,6 @@ static void pci_doe_flush_mb(void *mb) > /* 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); > } > > /** > @@ -429,19 +404,6 @@ struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset) > 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) { > @@ -496,23 +458,20 @@ 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 > + * @task: task to be run > * > - * 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->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 > + * 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) > { > if (!pci_doe_supports_prot(doe_mb, task->prot.vid, task->prot.type)) > return -EINVAL; > @@ -529,8 +488,8 @@ 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); > + exec_task(task); > + > 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..c94122a66221 100644 > --- a/include/linux/pci-doe.h > +++ b/include/linux/pci-doe.h > @@ -30,8 +30,6 @@ struct pci_doe_mb; > * @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 +48,6 @@ 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 +65,5 @@ 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 > > good to see that we can have a sync interface. I think that we still need some methods to garantee doe_task can be handled one by one in doe_mb? When more than one kernel thread are going to transfer data over a same doe_mb, only one kernel thread can use it and others will failed in exec_task(). Thanks Ming >>> OTOH using an on-stack structure for INIT_WORK seems rather strange. >>> Since the kernel thread must sleep waiting for the 'work' to complete >>> why not just perform the required code there. >> >> It is not strange if some task submitters want to wait while others do not. It >> was suggested that all submit task operations be async and the callers who >> wanted to be synchronous would wait like this. >> >> As Dan said there is a difference between submit_bio() and submit_bio_wait(). >> >> We have simply left the wait part up to the users who all wait right now. > > Yeah, my bad for jumping ahead to worry about async when it is not yet > needed.
