netdev - Re: [PATCH net v1] net: io_uring/zcrx: call netdev_queue_get_dma

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Message-ID: <842b9023-1b86-455b-9aaa-20cdf0234c35@davidwei.uk>
Date: Tue, 28 Oct 2025 15:44:05 -0700
From: David Wei <dw@...idwei.uk>
To: Jakub Kicinski <kuba@...nel.org>
Cc: io-uring@...r.kernel.org, netdev@...r.kernel.org,
 Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net v1] net: io_uring/zcrx: call
 netdev_queue_get_dma_dev() under instance lock

On 2025-10-28 15:38, Jakub Kicinski wrote:
> On Tue, 28 Oct 2025 14:26:39 -0700 David Wei wrote:
>> netdev ops must be called under instance lock or rtnl_lock, but
>> io_register_zcrx_ifq() isn't doing this for netdev_queue_get_dma_dev().
>>
>> Fix this by taking the instance lock.
>>
>> Opted to do this by hand instead of netdev_get_by_index_lock(), which is
>> an older helper that doesn't take netdev tracker.
> 
> Fixes tag missing.

Sorry, will add, keep forgetting this...

> 
> netdev_get_by_index_lock() + netdev_hold() would be a better choice indeed.
> Just a reference doesn't hold off device shutdown.

Got it, I'll switch to this.

> 
> Is there a chance to reorder the io_zcrx_create_area() call, keep
> holding the lock and call __net_mp_open_rxq() ?

Yeah, I also thought about it, wasn't sure if it was appropriate to
extend the critical section. I'll do this in v2.