Mahesh Salgaonkar [off-list ref] 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