Re: Possible regression between 4.9 and 4.13

[Mason <slash.tmp@free.fr>]

On 30/08/2017 11:37, Mason wrote:

> On 30/08/2017 11:07, Ard Biesheuvel wrote:
> 
>> Please don't forget to mention that this is quirky hardware that
>> depends on BROKEN because it multiplexes MMIO and config space
>> accesses in the same memory window without any locking whatsoever
>> (which would be difficult to do in the first place because we don't
>> use accessors for MMIO in the kernel).
> 
> You're right, it was in the back of my mind, but I didn't state
> it explicitly for the benefit of linux-usb readers.
> 
>> So how likely is it that you are attempting to read from the xhci
>> BAR window while a config space access is in progress? Any way to
>> instrument this in your driver?
> 
> I logged config space accesses here:
> 
> https://www.spinics.net/lists/arm-kernel/msg602832.html
> 
> IIRC, the config space accesses are generated by the AER ISR.
> So disabling the AER driver should guarantee that no config space
> accesses are occurring when the drive is unplugged.

I checked, and I *did* remember correctly.

Disabling the AER driver results in 0 config space access occurring
when the USB3 drive is unplugged. This confirms that the controller's
broken design (muxing config and mem space) is not responsible for
the glitches occurring on unplug events.

Furthermore, I confirm that once the controller has been deemed "dead",
even USB2 drives are no longer detected, and all USB port on the PCIe
board are disabled.

Regards.


For reads/writes in config space, I have:

	if (do_debug) {
		printk("\t READ: bus=%d devfn=%u where=%d size=%d val=0x%x\n",
			bus->number, devfn, where, size, *val);
		dump_stack();
	}

	if (do_debug) {
		printk("\tWRITE: bus=%d devfn=%u where=%d size=%d val=0x%x\n",
			bus->number, devfn, where, size, val);
		dump_stack();
	}

During setup I do get, e.g.

[    7.621417]   READ: bus=1 devfn=0 where=84 size=2 val=0x8
[    7.626840] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G         C      4.12.0-rc1 #2
[    7.634358] Hardware name: Sigma Tango DT
[    7.638387] [<c010e8b4>] (unwind_backtrace) from [<c010ac00>] (show_stack+0x10/0x14)
[    7.646171] [<c010ac00>] (show_stack) from [<c0257a30>] (dump_stack+0x84/0x98)
[    7.653429] [<c0257a30>] (dump_stack) from [<c029cb34>] (smp8759_config_read+0xa0/0xa4)
[    7.661474] [<c029cb34>] (smp8759_config_read) from [<c0282908>] (pci_bus_read_config_word+0x6c/0x94)
[    7.670742] [<c0282908>] (pci_bus_read_config_word) from [<c0282cfc>] (pci_read_config_word+0x24/0x38)
[    7.680097] [<c0282cfc>] (pci_read_config_word) from [<c028c5c0>] (__pci_dev_reset+0x11c/0x2fc)
[    7.688841] [<c028c5c0>] (__pci_dev_reset) from [<c028c9c4>] (pci_probe_reset_function+0xc/0x10)
[    7.697673] [<c028c9c4>] (pci_probe_reset_function) from [<c028f720>] (pci_create_sysfs_dev_files+0x2a8/0x374)
[    7.707728] [<c028f720>] (pci_create_sysfs_dev_files) from [<c0515cf8>] (pci_sysfs_init+0x34/0x54)
[    7.716734] [<c0515cf8>] (pci_sysfs_init) from [<c010175c>] (do_one_initcall+0x44/0x168)
[    7.724867] [<c010175c>] (do_one_initcall) from [<c0500dd8>] (kernel_init_freeable+0x15c/0x1e8)
[    7.733611] [<c0500dd8>] (kernel_init_freeable) from [<c0332348>] (kernel_init+0x8/0x108)
[    7.741831] [<c0332348>] (kernel_init) from [<c01076f8>] (ret_from_fork+0x14/0x3c)


On plug/unplug events, there are no config space accesses:

[   88.006750] usb 2-2: new SuperSpeed USB device number 2 using xhci_hcd
[   88.040179] usb 2-2: New USB device found, idVendor=0951, idProduct=1666
[   88.046930] usb 2-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[   88.054177] usb 2-2: Product: DataTraveler 3.0
[   88.058684] usb 2-2: Manufacturer: Kingston
[   88.062927] usb 2-2: SerialNumber: 002618887865F0C0F8646BFA
[   88.071523] usb-storage 2-2:1.0: USB Mass Storage device detected
[   88.081334] scsi host0: usb-storage 2-2:1.0
[   89.096074] scsi 0:0:0:0: Direct-Access     Kingston DataTraveler 3.0      PQ: 0 ANSI: 6
[   89.104828] sd 0:0:0:0: [sda] 15109516 512-byte logical blocks: (7.74 GB/7.20 GiB)
[   89.112996] sd 0:0:0:0: [sda] Write Protect is off
[   89.118060] sd 0:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[   89.129463]  sda: sda1
[   89.133104] sd 0:0:0:0: [sda] Attached SCSI removable disk

[  103.375210] xhci_hcd 0000:01:00.0: xHCI host controller not responding, assume dead
[  103.382917] xhci_hcd 0000:01:00.0: HC died; cleaning up
[  103.388281] usb 2-2: USB disconnect, device number 2