When we have a dependency of the form:
Device-A -> Device-C
Device-B
Device-C -> Device-B
Where,
* Indentation denotes "child of" parent in previous line.
* X -> Y denotes X is consumer of Y based on firmware (Eg: DT).
We have cyclic dependency: device-A -> device-C -> device-B -> device-A
fw_devlink current treats device-C -> device-B dependency as an invalid
dependency and doesn't enforce it but leaves the rest of the
dependencies as is.
While the current behavior is necessary, it is not sufficient if the
false dependency in this example is actually device-A -> device-C. When
this is the case, device-C will correctly probe defer waiting for
device-B to be added, but device-A will be incorrectly probe deferred by
fw_devlink waiting on device-C to probe successfully. Due to this, none
of the devices in the cycle will end up probing.
To fix this, we need to go relax all the dependencies in the cycle like
we already do in the other instances where fw_devlink detects cycles.
A real world example of this was reported[1] and analyzed[2].
[1] - https://lore.kernel.org/lkml/0a2c4106-7f48-2bb5-048e-8c001a7c3fda@samsung.com/
[2] - https://lore.kernel.org/lkml/CAGETcx8peaew90SWiux=TyvuGgvTQOmO4BFALz7aj0Za5QdNFQ@mail.gmail.com/
Fixes: f9aa460672 ("driver core: Refactor fw_devlink feature")
Cc: stable <stable@vger.kernel.org>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210915170940.617415-2-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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