Re: [PATCH net v4] usbnet: fix EVENT_RX_PAUSED race in usbnet_skb_return()

[sashiko-bot@kernel.org]

> On SMP, usbnet_skb_return() can observe EVENT_RX_PAUSED as set on CPU0
> while usbnet_resume_rx() clears the flag and drains rxq_pause on CPU1.
> The skb can then be queued after the drain has completed and remain
> stranded until the next MTU change or device stop.
> 
> Synchronize the EVENT_RX_PAUSED state transition and paused-queue
> dequeue operations with rxq_pause.lock, dropping the lock around each
> usbnet_skb_return() call to avoid lock inversion. In usbnet_skb_return()
> use a double-check pattern under rxq_pause.lock on the slow path,
> keeping the normal RX fast path lock-free. Use spin_lock_irqsave() to
> match the lockdep class shared with other sk_buff_head locks taken from
> hardirq context in defer_bh().
> 
> Discovered by Sashiko, not triggered, not runtime-tested.
> 
> Fixes: 43daa96b166c ("usbnet: Stop RX Q on MTU change")
> Signed-off-by: Ömer Mete Kaya <omermetekaya0@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261020153044.18828-1-omermetekaya0@gmail.com?part=1