Re: [PATCH] usb: xhci: check Null pointer in segment alloc

[Michal Pecio]

On Mon, 22 Dec 2025 12:03:45 -0500, Alan Stern wrote:
> There's not supposed to be an inappropriate time for doing an 
> autoresume.

> By the time the sound device's resume routine runs, the HC should be 
> fully resumed.

OK, if "should" means "supposed to" then somebody needs to check it.
Is this the HCD_FLAG_HW_ACCESSIBLE flag by any chance?

I see that devices recursively call bus_resume() before resuming, and
this fails with -ESHUTDOWN if the flag is unset, which seems to prevent
device resume from progressing further and crashing. Is this what is
meant to happen in such case?

So I guess it's not happening because xhci_resume() sets this flag
right away and then it may drop the lock and start deallocating memory
to reset everything. So we can "successfully" complete bus_resume()
and allow USB devices to resume while HC resume is still in progress.

Looks dodgy and I suspect this is the bug.