Re: [PATCH] powerpc/eeh: Delay slot presence check once driver is notified about the pci error.

[Michael Ellerman <mpe@ellerman.id.au>]

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 causes
> EEH recovery to fail and sometimes it leads to system hang or crash.
>
> ------------
> [52732.244731] DEBUG: ibm_read_slot_reset_state2()
> [52732.244762] DEBUG: ret = 0, rets[0]=5, rets[1]=1, rets[2]=4000, rets[3]=0x0
> [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 out
> [52736.564324] WARNING: CPU: 1442 PID: 0 at net/sched/sch_generic.c:478 dev_watchdog+0x438/0x440
> [...]
> [52736.564505] NIP [c000000000c32368] dev_watchdog+0x438/0x440
> [52736.564513] LR [c000000000c32364] dev_watchdog+0x434/0x440
> ------------
>
> To fix this issue, delay the slot presence check after notifying the driver
> about the pci error.

How does this interact with the commit that put the slot presence check
there in the first place:

  b104af5a7687 ("powerpc/eeh: Check slot presence state in eeh_handle_normal_event()")


It seems like delaying the slot presence check will effectively revert
that commit?

cheers