Re: [PATCH] scsi: cxlflash: Select SCSI_SCAN_ASYNC

On Tue, Feb 20, 2018 at 07:56:35PM +1100, Michael Ellerman wrote:

Vaibhav Jain [off-list ref] writes:

quoted

The cxlflash driver uses "Asynchronous SCSI scanning" enabled by
CONFIG_SCSI_SCAN_ASYNC. Without this enabled the modprobe of cxlflash
module gets hung with following backtrace:

Call Trace:
 __switch_to+0x2cc/0x470
 __schedule+0x288/0xab0
 schedule+0x40/0xc0
 schedule_timeout+0x254/0x4f0
 wait_for_common+0xdc/0x260
 flush_work+0x140/0x2a0
 work_on_cpu+0x88/0xb0
 pci_device_probe+0x1d0/0x220
 driver_probe_device+0x408/0x5b0
 __driver_attach+0x16c/0x1a0
 bus_for_each_dev+0xb8/0x110
 driver_attach+0x3c/0x60
 bus_add_driver+0x1d8/0x370
 driver_register+0x9c/0x180
 __pci_register_driver+0x74/0xa0
 init_cxlflash+0x158/0x1cc
 do_one_initcall+0x68/0x1e0
 do_init_module+0x90/0x254
 load_module+0x2f8c/0x3720
 SyS_finit_module+0xcc/0x140
 system_call+0x58/0x6c

Why does it "hang"? That's kind of bizarre, I would expect either a
build or runtime failure if a feature the driver requires is missing.

It hangs due to a bug in the driver. I briefly looked at it several
months back before getting distracted with other items. IIRC there
was an issue with the state machine.

quoted

diff --git a/drivers/scsi/cxlflash/Kconfig b/drivers/scsi/cxlflash/Kconfig
index a011c5dbf214..f054c1b0fff3 100644
--- a/drivers/scsi/cxlflash/Kconfig
+++ b/drivers/scsi/cxlflash/Kconfig

@@ -6,6 +6,7 @@ config CXLFLASH
 	tristate "Support for IBM CAPI Flash"
 	depends on PCI && SCSI && CXL && EEH
 	select IRQ_POLL
+	select SCSI_SCAN_ASYNC

It's user configurable, so it's rude to select it. It can also be
disabled on the kernel command line, so this seems like a fragile
solution.

I think Vaibhav's intention here was to avoid the hang while the bug
is still present - I believe he has encountered it several times recently.

The proper solution would be to fix the bug.