Re: [PATCH net-next] net: macb: move printk() calls out of bp->lock critical section

[Nicolai Buchwitz]

Hi Théo

On 30.9.2026 20:35, Théo Lebrun wrote:
> printk() call while bp->lock is acquired might be a bad idea:
>
>  - It grows the spinlock atomic section.
>
>  - If netconsole is active on the same interface (and we run on the
>    queue's CPU), we risk a deadlock because macb_poll_controller()
>    calls macb_interrupt() which grab bp->lock if an IRQ is pending.
>
> Three messages are changed:
>
>  - In macb_tx_error_task(), defer netdev_err("halt tx timed out") call
>    to after the critical section. Update the message to highlight it
>    occurred in the past. Inherit the buffer exhaustion boolean variable
>    name from the old code comment.
>
>  - In macb_tx_error_task(), defer the netdev_err("TX buffers exhausted
>    mid-frame") call out of the loop. This also means it goes from
>    1-per-error to 1-per-task-invocation.
>
>  - In IRQ handling, move HRESP error printing out of
>    macb_interrupt_misc() into macb_interrupt(). Again, it means we
>    dedup error reporting if status is read multiple times in a row with
>    HRESP bit set. This is fine as from past instances I've seen, this
>    message spams our log if it occurs.
>
> Notice we *ignore* debug printks; if you are debugging MACB maybe don't
> use netconsole...
>
> The netconsole deadlock is theoretical & never reproduced.
>
> Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
> ---
> This patch used to be part of context swapping V9.
> It got moved out as there aren't any dependency or relationship.
>
> Technically it is a fix, in practice I'm happy for it to go through
> net-next/main for more testing and it is a theoretical bugfix (as usual
> nowadays). Decided after seeing Jakub taking a similar patch into
> net-next this morning:
>
> > Since Linus is pushing back on our number of Fixes let's go for
> > net-next with similar fixes until the merge window
> https://lore.kernel.org/netdev/20260929184531.36ac3dc3@xxxxxxxxxx/
>
> Changes since context swapping v9:
> - Rebase onto latest net-next/main (47a144672573).
> - Send patch standalone.
> - Simplify the commit message (it was a long and partially wrong
>   rambling before). Also mention that it is a theoretical bugfix.
> - Link to v9: 
> https://patch.msgid.link/20260812-macb-context-v9-0-7ddbf5f715e0@xxxxxxxxxxx
> ---

> [...]

Reviewed-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>

Thanks,
Nicolai