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Message-ID: <39c213c17712fdc8877b4277b430bfded71c3cca.camel@codeconstruct.com.au>
Date: Fri, 17 Nov 2023 08:50:18 -0600
From: Matt Johnston <matt@...econstruct.com.au>
To: Jeremy Kerr <jk@...econstruct.com.au>, Jinliang Wang
<jinliangw@...gle.com>
Cc: William Kennington <wak@...gle.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mctp-i2c: increase the MCTP_I2C_TX_WORK_LEN to 500
Hi,
On Fri, 2023-11-17 at 15:29 +0800, Jeremy Kerr wrote:
> spin_lock_irqsave(&midev->tx_queue.lock, flags);
> if (skb_queue_len(&midev->tx_queue) >= MCTP_I2C_TX_WORK_LEN) {
> netif_stop_queue(dev);
> spin_unlock_irqrestore(&midev->tx_queue.lock, flags);
> netdev_err(dev, "BUG! Tx Ring full when queue awake!\n");
> return NETDEV_TX_BUSY;
> }
>
> __skb_queue_tail(&midev->tx_queue, skb);
> if (skb_queue_len(&midev->tx_queue) == MCTP_I2C_TX_WORK_LEN) // normal stop
> netif_stop_queue(dev);
> spin_unlock_irqrestore(&midev->tx_queue.lock, flags);
>
> What looks like has happened here:
>
> 1) we have TX_WORK_LEN-1 packets queued
> 2) we release a flow, which queues the "marker" skb. the tx_queue now
> has TX_WORK_LEN items
> 3) we queue another packet, ending up with TX_WORK_LEN+1 in the queue
> 4) the == TX_WORK_LEN test fails, so we dont do a netif_stop_queue()
>
> A couple of potential fixes:
>
> * We do the check and conditional netif_stop_queue() in (2)
> * We change the check there to be `>= MCTP_I2C_TX_WORK_LEN`
My inclination would be to change the second comparison (the normal stop
condition) to
/* -1 to allow space for an additional unlock_marker skb */
if (skb_queue_len(&midev->tx_queue) >= MCTP_I2C_TX_WORK_LEN-1)
Cheers,
Matt
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