Re: [PATCH v5] PCI hotplug: rpaphp: Error out on busy status from get-sensor-state

[Nathan Lynch <nathanl@linux.ibm.com>]

Mahesh Salgaonkar <mahesh@linux.ibm.com> writes:
> When certain PHB HW failure causes phyp to recover PHB, it marks the PE
> state as temporarily unavailable until recovery is complete. This also
> triggers an EEH handler in Linux which needs to notify drivers, and perform
> recovery. But before notifying the driver about the pci error it uses
> get_adapter_state()->get-sesnor-state() operation of the hotplug_slot to
> determine if the slot contains a device or not. if the slot is empty, the
> recovery is skipped entirely.
>
> However on certain PHB failures, the rtas call get-sesnor-state() returns
> extended busy error (9902) until PHB is recovered by phyp. Once PHB is
> recovered, the get-sensor-state() returns success with correct presence
> status. The rtas call interface rtas_get_sensor() loops over the rtas call
> on extended delay return code (9902) until the return value is either
> success (0) or error (-1). This causes the EEH handler to get stuck for ~6
> seconds before it could notify that the pci error has been detected and
> stop any active operations. Hence with running I/O traffic, during this 6
> seconds, the network driver continues its operation and hits a timeout
> (netdev watchdog). On timeouts, network driver go into ffdc capture mode
> and reset path assuming the PCI device is in fatal condition. This
> sometimes causes EEH recovery to fail. This impacts the ssh connection and
> leads to the system being inaccessible.
>
> ------------
> [52732.244731] DEBUG: ibm_read_slot_reset_state2()
> [52732.244762] DEBUG: ret = 0, rets[0]=5, rets[1]=1, rets[2]=4000, rets[3]=>
> [52732.244798] DEBUG: in eeh_slot_presence_check
> [52732.244804] DEBUG: error state check
> [52732.244807] DEBUG: Is slot hotpluggable
> [52732.244810] DEBUG: hotpluggable ops ?
> [52732.244953] DEBUG: Calling ops->get_adapter_status
> [52732.244958] DEBUG: calling rpaphp_get_sensor_state
> [52736.564262] ------------[ cut here ]------------
> [52736.564299] NETDEV WATCHDOG: enP64p1s0f3 (tg3): transmit queue 0 timed o>
> [52736.564324] WARNING: CPU: 1442 PID: 0 at net/sched/sch_generic.c:478 dev>
> [...]
> [52736.564505] NIP [c000000000c32368] dev_watchdog+0x438/0x440
> [52736.564513] LR [c000000000c32364] dev_watchdog+0x434/0x440
> ------------
>
> To avoid this issue, fix the pci hotplug driver (rpaphp) to return an error
> if the slot presence state can not be detected immediately while pe is in
> EEH recovery state. Current implementation uses rtas_get_sensor() API which
> blocks the slot check state until rtas call returns success. Change
> rpaphp_get_sensor_state() to invoke rtas_call(get-sensor-state) directly
> only if the respective pe is in EEH recovery state, and take actions based
> on rtas return status.
>
> In normal cases (non-EEH case) rpaphp_get_sensor_state() will continue to
> invoke rtas_get_sensor() as it was earlier with no change in existing
> behavior.
>
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
>
> ---
> Change in v5:
> - Fixup #define macros with parentheses around the values.
>
> Change in V4:
> - Error out on sensor busy only if pe is going through EEH recovery instead
>   of always error out.
>
> Change in V3:
> - Invoke rtas_call(get-sensor-state) directly from
>   rpaphp_get_sensor_state() directly and do special handling.
> - See v2 at
>   https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-November/237336.html
>
> Change in V2:
> - Alternate approach to fix the EEH issue instead of delaying slot presence
>   check proposed at
>   https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-November/236956.html
>
> Also refer:
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-November/237027.html

Sorry for the long delay. I think it looks OK now. Does this need to go
to the PCI list/maintainer?

Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com>