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CXL testing environment can trigger following trace
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000092: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000490-0x0000000000000497]
RIP: 0010:cxl_dpa_to_region+0x105/0x1f0 [cxl_core]
Call Trace:
<TASK>
cxl_event_trace_record+0xd1/0xa70 [cxl_core]
__cxl_event_trace_record+0x12f/0x1e0 [cxl_core]
cxl_mem_get_records_log+0x261/0x500 [cxl_core]
cxl_mem_get_event_records+0x7c/0xc0 [cxl_core]
cxl_mock_mem_probe+0xd38/0x1c60 [cxl_mock_mem]
platform_probe+0x9d/0x130
really_probe+0x1c8/0x960
__driver_probe_device+0x187/0x3e0
driver_probe_device+0x45/0x120
__device_attach_driver+0x15d/0x280
When CXL subsystem adds a cxl port to a hierarchy, there is a small
window where the new port becomes visible before it is bound to a
driver. This happens because device_add() adds a device to bus device
list before bus_probe_device() binds it to a driver.
So if two cxl memdevs are trying to add a dport to a same port via
devm_cxl_enumerate_ports(), the second cxl memdev may observe the port
and attempt to add a dport, but fails because the port has not yet been
attached to cxl port driver. That causes the memdev->endpoint can not be
updated.
The sequence is like:
CPU 0 CPU 1
devm_cxl_enumerate_ports()
# port not found, add it
add_port_attach_ep()
# hold the parent port lock
# to add the new port
devm_cxl_create_port()
device_add()
# Add dev to bus devs list
bus_add_device()
devm_cxl_enumerate_ports()
# found the port
find_cxl_port_by_uport()
# hold port lock to add a dport
device_lock(the port)
find_or_add_dport()
cxl_port_add_dport()
return -ENXIO because port->dev.driver is NULL
device_unlock(the port)
bus_probe_device()
# hold the port lock
# for attaching
device_lock(the port)
attaching the new port
device_unlock(the port)
To fix this race, require that dport addition holds the host lock
of the target port(the host of CXL root and all cxl host bridge ports is
the platform firmware device, the host of all other ports is their
parent port). The CXL subsystem already requires holding the host lock
while attaching a new port. Therefore, successfully acquiring the host
lock guarantees that port attaching has completed.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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