Re: [PATCH net-next v5 00/15] net: macb: implement context swapping
From: Théo Lebrun <theo.lebrun@bootlin.com>
Date: 2026-07-30 16:18:01
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Hello Paolo, On Thu Jul 30, 2026 at 1:52 PM CEST, Paolo Abeni wrote:
On 7/24/26 5:29 PM, Théo Lebrun wrote:quoted
MACB has a pretty primitive approach to buffer management. They are all stored in `struct macb *bp`. On operations that require buffer realloc (set_ringparam & change_mtu at the moment), the only option is to close the interface, change our global state and re-open the interface. Two issues: - It doesn't fly on memory pressured systems; we free our precious buffers and don't manage to reallocate fully, meaning our machine just lost its network access. - Anecdotally, it is pretty slow because it implies a full PHY reinit. Instead, we shall: - allocate a new context (including buffers) first - if it fails, early return without any impact to the interface - stop interface - update global state (bp, netdev, etc) - pass newly allocated buffer pointers to the hardware - start interface - free old context This is what we implement here. Both .set_ringparam() and .ndo_change_mtu() are covered by this series. In the future, at least .set_channels() [0], XDP [1] and XSK [2] would benefit. The change is super intrusive so conflicts will be major. Sorry! -- During iteration V3, the LLM raised many race conditions because BH features aren't disabled at close and might do a variety of bad things (interact with NAPI while disabled or re-arm IRQs). This is NOT fixed here. Here we focus on swap, not close. The series is way too long already.Note that Sashiko gemini has more to say: https://sashiko.dev/#/patchset/20260724-macb-context-v5-0-569b1852bc7f%40bootlin.com At least the possible deadlock in patch 13/15 looks real to me.
Thanks. I've patched it by moving printk() calls out of the bp->lock critical section. I'll appear in next revision.
Please also note net-next commit c82ff94592fb
Thanks for the hint, makes sense. I had heard "rumors" but didn't know it was official policy. I'll make a full pass before sending next revision (tomorrow probably). Thanks, -- Théo Lebrun, Bootlin Embedded Linux and Kernel engineering https://bootlin.com