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Date: Mon, 21 Nov 2022 10:07:56 +0800
From: "Li, Ming" <ming4.li@...el.com>
To: <ira.weiny@...el.com>
CC: Gregory Price <gregory.price@...verge.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Vishal Verma <vishal.l.verma@...el.com>,
Lukas Wunner <lukas@...ner.de>,
Alison Schofield <alison.schofield@...el.com>,
<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-pci@...r.kernel.org>,
Dan Williams <dan.j.williams@...el.com>,
Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI/DOE: Remove asynchronous task support
On 11/21/2022 9:39 AM, Li, Ming wrote:
> On 11/20/2022 6:25 AM, ira.weiny@...el.com wrote:
>> From: Ira Weiny <ira.weiny@...el.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]
>>
>> [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@...verge.com>
>> Reported-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> Suggested-by: Dan Williams <dan.j.williams@...el.com>
>> Suggested-by: "Li, Ming" <ming4.li@...el.com>
>> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
>>
>> ---
>> 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 | 83 ++++++++++++++---------------------------
>> include/linux/pci-doe.h | 10 +----
>> 3 files changed, 32 insertions(+), 77 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 e402f05068a5..41a75112b39b 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
>> + * @exec_lock: Lock to ensure 1 task is processed at a time
>> * @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 exec_lock;
>> unsigned long flags;
>> };
>>
>> @@ -211,7 +210,6 @@ 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 +229,8 @@ 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 +291,12 @@ 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 +304,13 @@ 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 +362,6 @@ 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;
>> @@ -390,12 +369,9 @@ static void pci_doe_flush_mb(void *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 */
>> + /* Cancel the in progress task and waiting tasks, if necessary */
>> set_bit(PCI_DOE_FLAG_CANCEL, &doe_mb->flags);
>> wake_up(&doe_mb->wq);
> should use wake_up_all() to wake up all waiting tasks here?
>
>> -
>> - /* Flush all work items */
>> - flush_workqueue(doe_mb->work_queue);
>> }
>>
>> /**
>> @@ -423,25 +399,13 @@ 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->exec_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) {
>> @@ -496,23 +460,22 @@ 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)
>> {
>> if (!pci_doe_supports_prot(doe_mb, task->prot.vid, task->prot.type))
>> return -EINVAL;
>> @@ -529,8 +492,18 @@ 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);
>> +
>> +again:
>> + if (!mutex_trylock(&doe_mb->exec_lock)) {
>> + if (wait_event_timeout(task->doe_mb->wq,
>> + test_bit(PCI_DOE_FLAG_CANCEL, &doe_mb->flags),
>> + PCI_DOE_POLL_INTERVAL))
>> + return -EIO;
>
> We already implemented a pci_doe_wait(), I think we can use it to instead of this wait_event_timeout.
>
> Thanks
> Ming
>
This wait_event_timeout() only check PCI_DOE_FLAG_CANCEL, that means it only detects the signal which the doe_mb has being destroyed.
If current doe task is done correctly, I think we should wake up next task. Current implementation just waits utill timeout happens and try it again.
Besides, If two threads are waiting a same doe_mb, thread #1 waited firstly, thread #2 waited secondly, there is a chance that thread #2 is processed before thread #1.
Thanks
Ming
>> + goto again;
>> + }
>> + exec_task(task);
>> + mutex_unlock(&doe_mb->exec_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..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
>>
>> base-commit: b6e7fdfd6f6a8bf88fcdb4a45da52c42ba238c25
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