Re: [REGRESSION] 6.12.36+: usb: hub: post-resume delayed work triggers > uncorrected MCE / data fabric sync flood on Threadripper 7970X > (bisected to aec11e5f9c45)

[Michal Pecio <michal.pecio@gmail.com>]

On Sun, 23 Aug 2026 13:44:53 +0200, Mathieu Fluhr wrote:
> Yes, looking at the reports, this looks definitely related.
> What is happening when the emulator starts is that it also starts adbd
> if not running on the Linux side, to communicate with the emulator
> later on.
> 
> [...]
>
> Ok, here you lost me a little: Looking to all the links provided, yes,
> this looks very similar to what I am experiencing. But (and correct me
> if I am wrong)
> 1. reverting the "bad commit" is not really an option, since it was
> originally authored for a specific purpose (other than annoying AMD
> owners :)

It does seem so, even if the specific issue report isn't known.

It also isn't clear (at least to me) whether the intended behavior of
the patch is causing this, or if the patch simply has some bug which
causes unintended side effects that can and should be fixed.

> 2. the patch that Mario proposed is very recent, and would address the
> issue not on the USB but on the PCI level?
> 
> Thanks again for the swift answer here and all the informative links!
> I must admit that I researched a lot debugging this issue, but I never
> thought about looking to the USB side of the problem, focusing more on
> the CPU side.

The issue is obviously a severe HW malfunction (you mentioned MCEs, the
Ryzen CPUs simply totally locked up), triggered by poking certain xHCI
controllers on the I/O die of these CPUs in some wrong way.

The minimum known trigger is this loop from bugzilla comment 8:

	while sleep .1 ; do true </dev/bus/usb/010/001 ; done

Opinions seem to vary on whether CPU load must be present or absent.

The minimum known workaround is disabling xHCI PCI function suspend,
see bugzilla comment 16. This knowledge has spread on distribution
forums and many users stopped caring about this bug, but clearly new
people are still running into it.

It seems USB devices and even the root hub can be suspended safely, as
long as the PCI function remains on full power. The influence of CPU
C-states was previously unknown. May be specific to Threadripper.

Regards,
Michal