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
Signed-off-by: Vaibhav Jain <redacted>
---
drivers/scsi/cxlflash/Kconfig | 1 +
1 file changed, 1 insertion(+)
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
default m
help
Allows CAPI Accelerated IO to Flash
--
2.14.3
Vaibhav Jain [off-list ref] writes:
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.
quoted hunk
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.
cheers
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.