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Date:   Wed, 2 Aug 2023 22:48:05 +0530
From:   Mahesh J Salgaonkar <mahesh@linux.ibm.com>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Nathan Lynch <nathanl@linux.ibm.com>,
        Tyrel Datwyler <tyreld@linux.ibm.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@ozlabs.org>,
        "Oliver O'Halloran" <oohall@gmail.com>,
        Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH v7 2/2] PCI: rpaphp: Error out on busy status from
 get-sensor-state
Message-ID: <d2iekrpa4ntky6ljqyo5rwqlq2c7e3m32etrgrkq223j736as6@gozot3d5llb3>
Reply-To: mahesh@linux.ibm.com
References: <169018891453.2762525.13358294392014600391.stgit@jupiter>
 <20230801213808.GA51837@bhelgaas>
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On 2023-08-01 16:38:08 Tue, Bjorn Helgaas wrote:
> On Mon, Jul 24, 2023 at 02:25:19PM +0530, Mahesh Salgaonkar wrote:
> > 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-sensor-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.
> 
> It's helpful to use the exact function name so it's greppable; I think
> get_adapter_status() or rpaphp_get_sensor_state()?
> 
> s/if the slot is empty,/If the slot is empty,/

Sure, will correct it in next revision.

> 
> > However on certain PHB failures, the RTAS call get-sensor-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).
> > 
> > ------------
> > [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
> > ------------
> > 
> > On timeouts, network driver starts dumping debug information to console
> > (e.g bnx2 driver calls bnx2x_panic_dump()), and go into recovery path while
> > pHyp is still recovering the PHB. As part of recovery, the driver tries to
> > reset the device and it keeps failing since every PCI read/write returns
> > ff's. And when EEH recovery kicks-in, the driver is unable to recover the
> > device. This impacts the ssh connection and leads to the system being
> > inaccessible. To get the NIC working again it needs a reboot or re-assign
> > the I/O adapter from HMC.
> > 
> > [ 9531.168587] EEH: Beginning: 'slot_reset'
> > [ 9531.168601] PCI 0013:01:00.0#10000: EEH: Invoking bnx2x->slot_reset()
> > [...]
> > [ 9614.110094] bnx2x: [bnx2x_func_stop:9129(enP19p1s0f0)]FUNC_STOP ramrod failed. Running a dry transaction
> > [ 9614.110300] bnx2x: [bnx2x_igu_int_disable:902(enP19p1s0f0)]BUG! Proper val not read from IGU!
> > [ 9629.178067] bnx2x: [bnx2x_fw_command:3055(enP19p1s0f0)]FW failed to respond!
> > [ 9629.178085] bnx2x 0013:01:00.0 enP19p1s0f0: bc 7.10.4
> > [ 9629.178091] bnx2x: [bnx2x_fw_dump_lvl:789(enP19p1s0f0)]Cannot dump MCP info while in PCI error
> > [ 9644.241813] bnx2x: [bnx2x_io_slot_reset:14245(enP19p1s0f0)]IO slot reset --> driver unload
> > [...]
> > [ 9644.241819] PCI 0013:01:00.0#10000: EEH: bnx2x driver reports: 'disconnect'
> > [ 9644.241823] PCI 0013:01:00.1#10000: EEH: Invoking bnx2x->slot_reset()
> > [ 9644.241827] bnx2x: [bnx2x_io_slot_reset:14229(enP19p1s0f1)]IO slot reset initializing...
> > [ 9644.241916] bnx2x 0013:01:00.1: enabling device (0140 -> 0142)
> > [ 9644.258604] bnx2x: [bnx2x_io_slot_reset:14245(enP19p1s0f1)]IO slot reset --> driver unload
> > [ 9644.258612] PCI 0013:01:00.1#10000: EEH: bnx2x driver reports: 'disconnect'
> > [ 9644.258615] EEH: Finished:'slot_reset' with aggregate recovery state:'disconnect'
> > [ 9644.258620] EEH: Unable to recover from failure from PHB#13-PE#10000.
> > [ 9644.261811] EEH: Beginning: 'error_detected(permanent failure)'
> > [...]
> > [ 9644.261823] EEH: Finished:'error_detected(permanent failure)'
> > 
> > Hence, it becomes important to inform driver about the PCI error detection
> > as early as possible, so that driver is aware of PCI error and waits for
> > EEH handler's next action for successful recovery.
> 
> I don't really understand the connection between EEH and
> get_adapter_status(), but I guess this probably refers to
> arch/powerpc/kernel/eeh_driver.c, not the PCI core aer.c and err.c?

Yup, EEH is an I/O error recovery mechanism on powerpc. On error during
during I/O operations on the PCI bus, EEH handler makes sure that the
error is not due to hotplug remove, before proceeding with recovery.
Depending on whether device is present or hot removed,
get_adapter_status() returns state as true or false respectively. Only
in certain failure cases it returns BUSY error.

eeh_event_handler()
  ->eeh_handle_normal_event()
    ->eeh_slot_presence_check()
      ->get_adapter_status(&state)
         skip recovery if state == false

> 
> > Current implementation uses rtas_get_sensor() API which blocks the slot
> > check state until RTAS call returns success. To avoid this, fix the PCI
> > hotplug driver (rpaphp) to return an error (-EBUSY) if the slot presence
> > state can not be detected immediately while PE is in EEH recovery state.
> > 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. This way EEH handler will not be
> > blocked on rpaphp_get_sensor_state() and can immediately notify driver
> > about the PCI error and stop any active operations.
> > 
> > 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>
> > Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com>
> 
> Seems like maybe both patches could go via a ppc tree since they seem
> very ppc-specific?  A couple minor comments below.
> 
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> 
> > + * get_adapter_status() can be called by the EEH handler during EEH recovery.
> > + * On certain PHB failures, the RTAS call get-seHsor-state() returns extended
> 
> Looks like a typo in "get-seHsor-state"?

ouch. Will fix it.

> 
> > +static int __rpaphp_get_sensor_state(struct slot *slot, int *state)
> > +{
> > +#ifdef CONFIG_EEH
> 
> Is this #ifdef redundant?  It looks like this file is only compiled
> if CONFIG_EEH is set:

Thansk for pointing this out. I missed this, yes it is redundant. Will
remove it.

> 
>   config HOTPLUG_PCI_RPA
>           tristate "RPA PCI Hotplug driver"
>           depends on PPC_PSERIES && EEH
> 
>   obj-$(CONFIG_HOTPLUG_PCI_RPA)           += rpaphp.o
> 
>   rpaphp-objs             :=      rpaphp_core.o   \
>                                   rpaphp_pci.o    \
>                                   rpaphp_slot.o

Thanks for your review.
-Mahesh