[Bug 217242] CPU hard lockup related to xhci/dma

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217242

--- Comment #18 from Austin Domino (austin.domino@hotmail.com) ---
I've narrowed down when this bug first appears to the 5.12 kernel release; I
ran a couple computers for a week on kernel version 5.11 and ran into 0
problems while running a program like the one above, but before doing this, I
had 1 of those computers on kernel version 5.12 while running that same program
with the same devices and it ran into this bug within 24 hours.


I looked at the number of TRBs for the computers that ran kernel version 5.11
for over a week with that program, and they were all at 512, so it's extremely
unlikely that the ring expansion problems are present in version 5.11.


This morning, out of curiosity, I took a computer running Ubuntu 18.04, went to
Ubuntu's kernel build page, https://kernel.ubuntu.com/~kernel-ppa/mainline/,
and tried a number of kernels to narrow down when the ring expansion problems
first appeared.  It seems that this problem is present in all the 5.12-rc
releases, and I know that it's present on 5.15; that was what this computer was
running before all of this, so I'm assuming that it's present from 5.12 onward.
 Right now I have this computer running kernel "v5.12-rc1" from Ubuntu's kernel
page, the ring expansion problems are present; the maximum number of TRBs for a
device the last time I checked was 8388608 after ~2.5 hours, and I'm curious if
this computer will run into a hard lockup.  I'm nearly certain that it will,
but we'll just have to wait and see to be certain.


Lastly, I went and looked at the changes that were done between v5.11 and
v5.12-rc2 within the "drivers/usb/host" directory and it appears that a
moderate amount of change took place (more than enough to make my head spin). 
I haven't dealt with kernel source like this before and it'd take a while to
parse through everything to understand what's going on, so I don't know how
much further I will get involved. Anyhow, I hope that this information might
help.

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