[Bug 221103] xhci_hcd: System lockup under CPU load during usbfs polling of USB devices on AMD platforms

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=221103

--- Comment #20 from Michał Pecio (michal.pecio@gmail.com) ---
Have you ever seen this "Controller not ready / post-resume error / HC died"
sequence without the machine hanging? It would probably be hard not to notice,
because the whole bus with all devices becomes unavailable.

This is coming from xhci_resume() calling xhci_handshake() and getting -ENODEV,
which means that the hardware malfunctions (or is misconfigured by PCI layer?)
and returns 0xffffffff on register read.

I patched this code to pretend that it happened and I got the same log
messages, but still no crash or freeze.

Maybe I need to try it a few more times, but it seems that real users are
seeing a hang every time the HC dies while opening /dev/bus/usb/ files, because
otherwise we would get a separate bug about "HC died" and loss of all devices
when running ADB. Or maybe not, because the bus being suspended means that
nobody is actively using its devices, so nobody would notice if they
disappear...

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