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

[bugzilla-daemon@kernel.org]

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

--- Comment #17 from Mathias Nyman (mathias.nyman@linux.intel.com) ---
Thanks, one reason why ring expansion calculation is incorrect is that we try
to store a negative value in an unsigned int. 

static int prepare_ring(...)
{
        unsigned int num_trbs_needed;        
        ....
        num_trbs_needed = num_trbs - ep_ring->num_trbs_free;
}

ep_ring->num_trbs_free might be bigger than num_trbs

So we end up with a huge and incorrect num_trbs_needed

https://elixir.bootlin.com/linux/v6.2/source/drivers/usb/host/xhci-ring.c#L3186

In addition to this there is most likely a small bug in tracking
ep_ring->num_trbs_free, gradually decreasing it incorrectly.
Not sure where that happens

Still working on that debugging patch

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