linux-kernel - Re: [PATCH 1/3] usb: xhci: Simplify update_ring_for_set_deq

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Message-ID: <20250305092411.6962ca52@foxbook>
Date: Wed, 5 Mar 2025 09:24:11 +0100
From: Michał Pecio <michal.pecio@...il.com>
To: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: Mathias Nyman <mathias.nyman@...el.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org, Niklas Neronin
 <niklas.neronin@...ux.intel.com>
Subject: Re: [PATCH 1/3] usb: xhci: Simplify
 update_ring_for_set_deq_completion()

On Fri, 21 Feb 2025 15:23:11 +0200, Mathias Nyman wrote:
> update_ring_for_set_deq_completion() isn't needed anymore.
> Niklas already wrote a patch to remove it.
> 
> It's sitting in my for-usb-next branch
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/commit/?h=for-usb-next&id=ee7dab196a7dfc48a1608274329323cb10b4340d

I know that it's pure paranoia, but this patch removes a quiet debug
message about an obviously abnormal and likely harmful condition.

My patch turned it into a nice red error.

This will be something to keep in mind, for example somebody could
write a patch which reclaims an empty transfer ring segment without
chceking if there is a Set TR Dequeue pending to this segemnt. That
could lead to very interesting outcomes if all TRBs in the segment
are No-Op'ed and the next page is a transfer ring of other endpoint.

Other than that, I suppose there is currently no problem. The loop
for finding new dequeue position doesn't seem prone to jumping off
the ring as long as the ring itself isn't corrupted.

Michal