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

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> > >>>>>> 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.
> > >>>>>> 2. The application should stop data path API invocation when process
> > >>>>>>     the RTE_ETH_EVENT_ERR_RECOVERING event.
> > >>>>>> 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.
> > >>>>>>
> > >>>>
> > >>>> How this is solving the race-condition, by pushing responsibility to
> > >>>> stop data path to application?
> > >>>
> > >>> Exactly, it becomes application responsibility to make sure data-path is
> > >>> stopped/suspended before recovery will continue.
> > >>>
> > >>
> > >> From documentation of the feature:
> > >>
> > >> ``
> > >> 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.
> > >>
> > >> In order to sense the error happening/recovering, as well as to restore
> > >> some additional configuration, three events are available:
> > >> ``
> > >>
> > >> It looks like initial design is to use events mainly inform application
> > >> about what happened and mainly for re-configuration.
> > >>
> > >> Although I am don't disagree to involve the application, I am not sure
> > >> that is part of current design.
> > >
> > > I thought we all agreed that initial design contain some fallacies that
> > > need to fixed, no?
> > > Statement that with current rte_ethdev design error recovery can be done
> > > without interaction with the app (to stop/suspend data/control path)
> > > is the main one I think.
> > > It needs some interaction with app layer, one way or another.
> > >
> > >>>>
> > >>>> What if application is not interested in recovery modes at all and not
> > >>>> registered any callback for the recovery?
> > >>>
> > >>>
> > >>> Are you saying there is no way for application to disable
> > >>> automatic recovery in PMD if it is not interested
> > >>> (or can't full-fill per-requesties for it)?
> > >>> If so, then yes it is a problem and we need to fix it.
> > >>> I assumed that such mechanism to disable unwanted events already exists,
> > >>> but I can't find anything.
> > >>> Wonder what would be the easiest way here - can PMD make a decision
> > >>> based on callback return value, or do we need a new API to
> > >>> enable/disable callbacks, or ...?
> > >>>
> > >>>
> > >>
> > >> As far as I can see automatic recovery is not configurable by app.
> > >>
> > >> But that is not all, PMD sends events to application but PMD can't know
> > >> if application is handling them or not, so with current design PMD can't
> > >> rely on to app.
> > >
> > > Well, PMD invokes user provided callback.
> > > One way to fix that problem - if there is no callback provided,
> > > or callback returns an error code - PMD can assume that recovery
> > > should not be done.
> > > That is probably not the best design choice, but at least it will allow
> > > to fix the problem without too many changes and introducing new API.
> > > That could be sort of a 'quick fix'.
> > > In a meanwhile we can think about new/better approach for that.
> > >
> >
> > -rc2 for 23.03 is a few days away.
> >
> > What do you think to have 'quick fix' as modifying how driver updates
> > burst ops to prevent the race condition, for this release?
> >
> > And plan a design update for the next release?
> +1 on the overall approach.

Yep, agree.
 
> 
> >
> >
> > >>
> > >>>> I think driver should not rely on application for this, unless
> > >>>> application explicitly says (to driver) that it is handling recovery,
> > >>>> right now there is no way for driver to know this.
> > >>>
> > >>> I think it is visa-versa:
> > >>> application should not enable auto-recovery if it can't meet
> > >>> per-requeststies for it (provide appropriate callback).
> > >>>
> > >>
> > >> I agree on above, we are saying similar thing in different perspective.
> > >
> > > Ok, that's good we are on the same page.
> > >
> > >
> > >>
> > >>>
> > >>>>
> > >>>>>> 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
> > >>>>>> +   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.
> > >>>>>> +     *
> > >>>>>>        * @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,
> > >>>>>>       /** 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;
> > >>>>>> --
> > >>>>>   Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
> > >>>>>
> > >>>>>> 2.17.1
> > >>>>>
> > >>>>
> > >>>
> > >
> >