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

[Ajit Khaparde <ajit.khaparde@broadcom.com>]

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On Mon, Mar 6, 2023 at 3:00 AM Ferruh Yigit <ferruh.yigit@amd.com> wrote:
>
> On 3/6/2023 10:22 AM, Konstantin Ananyev wrote:
> >
> >
> >>>>>> 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.

>
>
> >>
> >>>> 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
> >>>>>
> >>>>
> >>>
> >
>

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