Subject: Re: [v2] powerpc/eeh: Fix race with driver un/bind

From: Michael Ellerman <[email-masked]>
Date: Sun, 1 Apr 2018 01:04:01 +1100 (AEDT)

On Mon, 2018-03-26 at 04:17:07 UTC, Michael Neuling wrote:
> The current EEH callbacks can race with a driver unbind. This
> can result in a backtraces like this:
> 
> [    7.573055] EEH: Frozen PHB#0-PE#1fc detected
> [    7.573063] EEH: PE location: S000009, PHB location: N/A
> [    7.573069] CPU: 2 PID: 2312 Comm: kworker/u258:3 Not tainted 4.15.6-openpower1 #2
> [    7.573078] Workqueue: nvme-wq nvme_reset_work [nvme]
> [    7.573080] Call Trace:
> [    7.573088] [c000000ff12a3a30] [c0000000005f5000] dump_stack+0x9c/0xd0
> [    7.573093]  (unreliable)
> [    7.573106] [c000000ff12a3a70] [c00000000002385c] eeh_dev_check_failure+0x420/0x470
> [    7.573111] [c000000ff12a3b10] [c00000000002394c] eeh_check_failure+0xa0/0xa4
> [    7.573115] [c000000ff12a3b50] [c0080000088c2ff0] nvme_reset_work+0x138/0x1414 [nvme]
> [    7.573122] [c000000ff12a3cb0] [c000000000089c78] process_one_work+0x1ec/0x328
> [    7.573132] [c000000ff12a3d40] [c00000000008a3b4] worker_thread+0x2e4/0x3a8
> [    7.573140] [c000000ff12a3dc0] [c00000000008fed0] kthread+0x14c/0x154
> [    7.573150] [c000000ff12a3e30] [c00000000000b594] ret_from_kernel_thread+0x5c/0xc8
> [    7.573183] nvme nvme1: Removing after probe failure status: -19
> <snip>
> cpu 0x23: Vector: 300 (Data Access) at [c000000ff50f3800]
>     pc: c0080000089a0eb0: nvme_error_detected+0x4c/0x90 [nvme]
>     lr: c000000000026564: eeh_report_error+0xe0/0x110
>     sp: c000000ff50f3a80
>    msr: 9000000000009033
>    dar: 400
>  dsisr: 40000000
>   current = 0xc000000ff507c000
>   paca    = 0xc00000000fdc9d80   softe: 0        irq_happened: 0x01
>     pid   = 782, comm = eehd
> Linux version 4.15.6-openpower1 (smc@smc-desktop) (gcc version 6.4.0 (Buildroot 2017.11.2-00008-g4b6188e)) #2 SM                                             P Tue Feb 27 12:33:27 PST 2018
> enter ? for help
> [c000000ff50f3af0] c000000000026564 eeh_report_error+0xe0/0x110
> [c000000ff50f3b30] c000000000025520 eeh_pe_dev_traverse+0xc0/0xdc
> [c000000ff50f3bc0] c000000000026bd0 eeh_handle_normal_event+0x184/0x4c4
> [c000000ff50f3c70] c000000000026ff4 eeh_handle_event+0x30/0x288
> [c000000ff50f3d10] c00000000002758c eeh_event_handler+0x124/0x170
> [c000000ff50f3dc0] c00000000008fed0 kthread+0x14c/0x154
> [c000000ff50f3e30] c00000000000b594 ret_from_kernel_thread+0x5c/0xc8
> 
> The first part is an EEH (on boot), the second half is the resulting
> crash. nvme probe starts the nvme_reset_work() worker thread. This
> worker thread starts touching the device which see a device error
> (EEH) and hence queues up an event in the powerpc EEH worker
> thread. nvme_reset_work() then continues and runs
> nvme_remove_dead_ctrl_work() which results in unbinding the driver
> from the device and hence releases all resources. At the same time,
> the EEH worker thread starts doing the EEH .error_detected() driver
> callback, which no longer works since the resources have been freed.
> 
> This fixes the problem in the same way the generic PCIe AER code (in
> drivers/pci/pcie/aer/aerdrv_core.c) does. It makes the EEH code hold
> the device_lock() while performing the driver EEH callbacks and
> associated code. This ensures either the callbacks are no longer
> register, or if they are registered the driver will not be removed
> from underneath us.
> 
> This has been broken forever. The EEH call backs were first introduced
> in 2005 (in 77bd7415610) but it's not clear if a lock was needed back
> then.
> 
> Signed-off-by: Michael Neuling <[email-masked]>
> Cc: [email-masked]
> Reviewed-by: Benjamin Herrenschmidt <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/f0295e047fcf52ccb42561fb7de694

cheers