netdev - Re: [PATCH net] vmxnet3: Fix tx queue race condition with XDP

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Message-ID: <20250127170110.GE5024@kernel.org>
Date: Mon, 27 Jan 2025 17:01:10 +0000
From: Simon Horman <horms@...nel.org>
To: Sankararaman Jayaraman <sankararaman.jayaraman@...adcom.com>
Cc: netdev@...r.kernel.org, ronak.doshi@...adcom.com,
	bcm-kernel-feedback-list@...adcom.com, andrew+netdev@...n.ch,
	davem@...emloft.net, u9012063@...il.com, kuba@...nel.org,
	edumazet@...gle.com, pabeni@...hat.com, ast@...nel.org,
	alexandr.lobakin@...el.com, alexanderduyck@...com,
	bpf@...r.kernel.org, daniel@...earbox.net, hawk@...nel.org,
	john.fastabend@...il.com
Subject: Re: [PATCH net] vmxnet3: Fix tx queue race condition with XDP

On Fri, Jan 24, 2025 at 02:32:11PM +0530, Sankararaman Jayaraman wrote:
> If XDP traffic runs on a CPU which is greater than or equal to
> the number of the Tx queues of the NIC, then vmxnet3_xdp_get_tq()
> always picks up queue 0 for transmission as it uses reciprocal scale
> instead of simple modulo operation.
> 
> vmxnet3_xdp_xmit() and vmxnet3_xdp_xmit_frame() use the above
> returned queue without any locking which can lead to race conditions
> when multiple XDP xmits run in parallel on different CPU's.
> 
> This patch uses a simple module scheme when the current CPU equals or
> exceeds the number of Tx queues on the NIC. It also adds locking in
> vmxnet3_xdp_xmit() and vmxnet3_xdp_xmit_frame() functions.
> 
> Fixes: 54f00cce1178 ("vmxnet3: Add XDP support.")
> Signed-off-by: Sankararaman Jayaraman <sankararaman.jayaraman@...adcom.com>
> Signed-off-by: Ronak Doshi <ronak.doshi@...adcom.com>

Reviewed-by: Simon Horman <horms@...nel.org>