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fw_devlink can detect most overlapping/intersecting cycles. However it was
missing a few corner cases because of an incorrect optimization logic that
tries to avoid repeating cycle detection for devices that are already
marked as part of a cycle.
Here's an example provided by Xu Yang (edited for clarity):
usb
+-----+
tcpc | |
+-----+ | +--|
| |----------->|EP|
|--+ | | +--|
|EP|<-----------| |
|--+ | | B |
| | +-----+
| A | |
+-----+ |
^ +-----+ |
| | | |
+-----| C |<--+
| |
+-----+
usb-phy
Node A (tcpc) will be populated as device 1-0050.
Node B (usb) will be populated as device 38100000.usb.
Node C (usb-phy) will be populated as device 381f0040.usb-phy.
The description below uses the notation:
consumer --> supplier
child ==> parent
1. Node C is populated as device C. No cycles detected because cycle
detection is only run when a fwnode link is converted to a device link.
2. Node B is populated as device B. As we convert B --> C into a device
link we run cycle detection and find and mark the device link/fwnode
link cycle:
C--> A --> B.EP ==> B --> C
3. Node A is populated as device A. As we convert C --> A into a device
link, we see it's already part of a cycle (from step 2) and don't run
cycle detection. Thus we miss detecting the cycle:
A --> B.EP ==> B --> A.EP ==> A
Looking at it another way, A depends on B in one way:
A --> B.EP ==> B
But B depends on A in two ways and we only detect the first:
B --> C --> A
B --> A.EP ==> A
To detect both of these, we remove the incorrect optimization attempt in
step 3 and run cycle detection even if the fwnode link from which the
device link is being created has already been marked as part of a cycle.
Reported-by: Xu Yang <xu.yang_2@nxp.com>
Closes: https://lore.kernel.org/lkml/DU2PR04MB8822693748725F85DC0CB86C8C792@DU2PR04MB8822.eurprd04.prod.outlook.com/
Fixes: 3fb16866b51d ("driver core: fw_devlink: Make cycle detection more robust")
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20240202095636.868578-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
6442d79d88