Re: Kernel Panic in skb_release_data using genet

On Tue, Jun 01, 2021 at 11:33:18AM +0200, nicolas saenz julienne wrote:

On Mon, 2021-05-31 at 19:36 -0700, Florian Fainelli wrote:

quoted

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That is also how I boot my Pi4 at home, and I suspect you are right, if
the VPU does not shut down GENET's DMA, and leaves buffer addresses in
the on-chip descriptors that point to an address space that is managed
totally differently by Linux, then we can have a serious problem and
create some memory corruption when the ring is being reclaimed. I will
run a few experiments to test that theory and there may be a solution
using the SW_INIT reset controller to have a big reset of the controller
before handing it over to the Linux driver.

Adding a WARN_ON(reg & DMA_EN) in bcmgenet_dma_disable() has not shown
that the TX or RX DMA have been left running during the hand over from
the VPU to the kernel. I checked out drm-misc-next-2021-05-17 to reduce
as much as possible the differences between your set-up and my set-up
but so far have not been able to reproduce the crash in booting from NFS
repeatedly, I will try again.

FWIW I can reproduce the error too. That said it's rather hard to reproduce,
something in the order of 1 failure every 20 tries.

Yeah, it looks like it's only from a cold boot and comes in "bursts",
where you would get like 5 in a row and be done with it for a while.

Maxime