RE: [PATCH 1/5] ethdev: fix race-condition of proactive error handling mode

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> -----Original Message-----
> From: Chengwen Feng <fengchengwen@huawei.com>
> Sent: Tuesday, February 28, 2023 9:06 PM
> To: thomas@monjalon.net; ferruh.yigit@amd.com;
> konstantin.ananyev@huawei.com; Andrew Rybchenko
> <andrew.rybchenko@oktetlabs.ru>; Kalesh AP <kalesh-
> anakkur.purayil@broadcom.com>; Ajit Khaparde
> (ajit.khaparde@broadcom.com) <ajit.khaparde@broadcom.com>
> Cc: dev@dpdk.org
> Subject: [PATCH 1/5] ethdev: fix race-condition of proactive error handling
> mode
> 
> In the proactive error handling mode, the PMD will set the data path pointers to
> dummy functions and then try recovery, in this period the application may still
> invoking data path API. This will introduce a race-condition with data path which
> may lead to crash [1].
> 
> Although the PMD added delay after setting data path pointers to cover the
> above race-condition, it reduces the probability, but it doesn't solve the
> problem.
> 
> To solve the race-condition problem fundamentally, the following requirements
> are added:
> 1. The PMD should set the data path pointers to dummy functions after
>    report RTE_ETH_EVENT_ERR_RECOVERING event.
Do you mean to say, PMD should set the data path pointers after calling the call back function?
The PMD is running in the context of multiple EAL threads. How do these threads synchronize such that only one thread sets these data pointers?

> 2. The application should stop data path API invocation when process
>    the RTE_ETH_EVENT_ERR_RECOVERING event.
Any thoughts on how an application can do this?

> 3. The PMD should set the data path pointers to valid functions before
>    report RTE_ETH_EVENT_RECOVERY_SUCCESS event.
> 4. The application should enable data path API invocation when process
>    the RTE_ETH_EVENT_RECOVERY_SUCCESS event.
Do you mean to say that the application should not call the datapath APIs while the PMD is running the recovery process?

> 
> Also, this patch introduce a driver internal function rte_eth_fp_ops_setup
> which used as an help function for PMD.
> 
> [1]
> http://patchwork.dpdk.org/project/dpdk/patch/20230220060839.1267349-2-
> ashok.k.kaladi@intel.com/
> 
> Fixes: eb0d471a8941 ("ethdev: add proactive error handling mode")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
>  doc/guides/prog_guide/poll_mode_drv.rst | 20 +++++++---------
>  lib/ethdev/ethdev_driver.c              |  8 +++++++
>  lib/ethdev/ethdev_driver.h              | 10 ++++++++
>  lib/ethdev/rte_ethdev.h                 | 32 +++++++++++++++----------
>  lib/ethdev/version.map                  |  1 +
>  5 files changed, 46 insertions(+), 25 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/poll_mode_drv.rst
> b/doc/guides/prog_guide/poll_mode_drv.rst
> index c145a9066c..e380ff135a 100644
> --- a/doc/guides/prog_guide/poll_mode_drv.rst
> +++ b/doc/guides/prog_guide/poll_mode_drv.rst
> @@ -638,14 +638,9 @@ different from the application invokes recovery in
> PASSIVE mode,  the PMD automatically recovers from error in PROACTIVE
> mode,  and only a small amount of work is required for the application.
> 
> -During error detection and automatic recovery, -the PMD sets the data path
> pointers to dummy functions -(which will prevent the crash), -and also make
> sure the control path operations fail with a return code ``-EBUSY``.
> -
> -Because the PMD recovers automatically, -the application can only sense that
> the data flow is disconnected for a while -and the control API returns an error in
> this period.
> +During error detection and automatic recovery, the PMD sets the data
> +path pointers to dummy functions and also make sure the control path
> +operations failed with a return code ``-EBUSY``.
> 
>  In order to sense the error happening/recovering,  as well as to restore some
> additional configuration, @@ -653,9 +648,9 @@ three events are available:
> 
>  ``RTE_ETH_EVENT_ERR_RECOVERING``
>     Notify the application that an error is detected
> -   and the recovery is being started.
> +   and the recovery is about to start.
>     Upon receiving the event, the application should not invoke
> -   any control path function until receiving
> +   any control and data path API until receiving
>     ``RTE_ETH_EVENT_RECOVERY_SUCCESS`` or
> ``RTE_ETH_EVENT_RECOVERY_FAILED`` event.
> 
>  .. note::
> @@ -666,8 +661,9 @@ three events are available:
> 
>  ``RTE_ETH_EVENT_RECOVERY_SUCCESS``
>     Notify the application that the recovery from error is successful,
> -   the PMD already re-configures the port,
> -   and the effect is the same as a restart operation.
> +   the PMD already re-configures the port.
> +   The application should restore some additional configuration, and then
What is the additional configuration? Is this specific to each NIC/PMD?
I thought, this is an auto recovery process and the application does not require to reconfigure anything. If the application has to restore the configuration, how does auto recovery differ from typical recovery process?

> +   enable data path API invocation.
> 
>  ``RTE_ETH_EVENT_RECOVERY_FAILED``
>     Notify the application that the recovery from error failed, diff --git
> a/lib/ethdev/ethdev_driver.c b/lib/ethdev/ethdev_driver.c index
> 0be1e8ca04..f994653fe9 100644
> --- a/lib/ethdev/ethdev_driver.c
> +++ b/lib/ethdev/ethdev_driver.c
> @@ -515,6 +515,14 @@ rte_eth_dma_zone_free(const struct rte_eth_dev
> *dev, const char *ring_name,
>  	return rc;
>  }
> 
> +void
> +rte_eth_fp_ops_setup(struct rte_eth_dev *dev) {
> +	if (dev == NULL)
> +		return;
> +	eth_dev_fp_ops_setup(rte_eth_fp_ops + dev->data->port_id, dev); }
> +
>  const struct rte_memzone *
>  rte_eth_dma_zone_reserve(const struct rte_eth_dev *dev, const char
> *ring_name,
>  			 uint16_t queue_id, size_t size, unsigned int align, diff -
> -git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h index
> 2c9d615fb5..0d964d1f67 100644
> --- a/lib/ethdev/ethdev_driver.h
> +++ b/lib/ethdev/ethdev_driver.h
> @@ -1621,6 +1621,16 @@ int
>  rte_eth_dma_zone_free(const struct rte_eth_dev *eth_dev, const char
> *name,
>  		 uint16_t queue_id);
> 
> +/**
> + * @internal
> + * Setup eth fast-path API to ethdev values.
> + *
> + * @param dev
> + *  Pointer to struct rte_eth_dev.
> + */
> +__rte_internal
> +void rte_eth_fp_ops_setup(struct rte_eth_dev *dev);
> +
>  /**
>   * @internal
>   * Atomically set the link status for the specific device.
> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h index
> 049641d57c..44ee7229c1 100644
> --- a/lib/ethdev/rte_ethdev.h
> +++ b/lib/ethdev/rte_ethdev.h
> @@ -3944,25 +3944,28 @@ enum rte_eth_event_type {
>  	 */
>  	RTE_ETH_EVENT_RX_AVAIL_THRESH,
>  	/** Port recovering from a hardware or firmware error.
> -	 * If PMD supports proactive error recovery,
> -	 * it should trigger this event to notify application
> -	 * that it detected an error and the recovery is being started.
> -	 * Upon receiving the event, the application should not invoke any
> control path API
> -	 * (such as rte_eth_dev_configure/rte_eth_dev_stop...) until receiving
> -	 * RTE_ETH_EVENT_RECOVERY_SUCCESS or
> RTE_ETH_EVENT_RECOVERY_FAILED event.
> -	 * The PMD will set the data path pointers to dummy functions,
> -	 * and re-set the data path pointers to non-dummy functions
> -	 * before reporting RTE_ETH_EVENT_RECOVERY_SUCCESS event.
> -	 * It means that the application cannot send or receive any packets
> -	 * during this period.
> +	 *
> +	 * If PMD supports proactive error recovery, it should trigger this
> +	 * event to notify application that it detected an error and the
> +	 * recovery is about to start.
> +	 *
> +	 * Upon receiving the event, the application should not invoke any
> +	 * control and data path API until receiving
> +	 * RTE_ETH_EVENT_RECOVERY_SUCCESS or
> RTE_ETH_EVENT_RECOVERY_FAILED
> +	 * event.
> +	 *
> +	 * Once this event is reported, the PMD will set the data path pointers
> +	 * to dummy functions, and re-set the data path pointers to valid
> +	 * functions before reporting RTE_ETH_EVENT_RECOVERY_SUCCESS
> event.
Why do we need to set the data path pointers to dummy functions if the application is restricted from invoking any control and data path APIs till the recovery process is completed?

> +	 *
>  	 * @note Before the PMD reports the recovery result,
>  	 * the PMD may report the RTE_ETH_EVENT_ERR_RECOVERING event
> again,
>  	 * because a larger error may occur during the recovery.
>  	 */
>  	RTE_ETH_EVENT_ERR_RECOVERING,
I understand this is not a change in this patch. But, just wondering, what is the purpose of this? How is the application supposed to use this?

>  	/** Port recovers successfully from the error.
> -	 * The PMD already re-configured the port,
> -	 * and the effect is the same as a restart operation.
> +	 *
> +	 * The PMD already re-configured the port:
>  	 * a) The following operation will be retained: (alphabetically)
>  	 *    - DCB configuration
>  	 *    - FEC configuration
> @@ -3989,6 +3992,9 @@ enum rte_eth_event_type {
>  	 *      (@see RTE_ETH_DEV_CAPA_FLOW_SHARED_OBJECT_KEEP)
>  	 * c) Any other configuration will not be stored
>  	 *    and will need to be re-configured.
> +	 *
> +	 * The application should restore some additional configuration
> +	 * (see above case b/c), and then enable data path API invocation.
>  	 */
>  	RTE_ETH_EVENT_RECOVERY_SUCCESS,
>  	/** Port recovery failed.
> diff --git a/lib/ethdev/version.map b/lib/ethdev/version.map index
> 357d1a88c0..c273e0bdae 100644
> --- a/lib/ethdev/version.map
> +++ b/lib/ethdev/version.map
> @@ -320,6 +320,7 @@ INTERNAL {
>  	rte_eth_devices;
>  	rte_eth_dma_zone_free;
>  	rte_eth_dma_zone_reserve;
> +	rte_eth_fp_ops_setup;
>  	rte_eth_hairpin_queue_peer_bind;
>  	rte_eth_hairpin_queue_peer_unbind;
>  	rte_eth_hairpin_queue_peer_update;
> --
> 2.17.1