Re: [PATCH net] net: thunder_bgx: Fix netdev structure allocation

On Tue, 13 Aug 2024 17:25:27 +0100,
Breno Leitao [off-list ref] wrote:

Hello Marc,

On Mon, Aug 12, 2024 at 03:13:22PM +0100, Marc Zyngier wrote:

quoted

Commit 94833addfaba ("net: thunderx: Unembed netdev structure") had
a go at dynamically allocating the netdev structures for the thunderx_bgx
driver.  This change results in my ThunderX box catching fire (to be fair,
it is what it does best).

Should I be proud of it? :-)

It's always good practice to check that someone still cares about
terrible HW. Break it, wait for a few releases, and purge it if nobody
was looking.

Unfortunately, this is one of the few machines I have that has 16kB
page support, so I can't really turn a blind eye on the
breakage... ;-)

quoted

The issues with this change are that:

- bgx_lmac_enable() is called *after* bgx_acpi_register_phy() and
  bgx_init_of_phy(), both expecting netdev to be a valid pointer.

- bgx_init_of_phy() populates the MAC addresses for *all* LMACs
  attached to a given BGX instance, and thus needs netdev for each of
  them to have been allocated.

There is a few things to be said about how the driver mixes LMAC and
BGX states which leads to this sorry state, but that's beside the point.

To address this, go back to a situation where all netdev structures
are allocated before the driver starts relying on them, and move the
freeing of these structures to driver removal. Someone brave enough
can always go and restructure the driver if they want.

Fixes: 94833addfaba ("net: thunderx: Unembed netdev structure")
Signed-off-by: Marc Zyngier <maz@kernel.org>

Reviewed-by: Breno Leitao <leitao@debian.org>

Thanks for taming my fiery commit.

No worries.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.