netdev - Re: [PATCH net v2] net: stmmac: fix transmit queue timed out after resume

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Message-ID: <aWd9WUUGhSU5tWcn@shell.armlinux.org.uk>
Date: Wed, 14 Jan 2026 11:26:17 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Tao Wang <tao03.wang@...izon.auto>
Cc: kuba@...nel.org, alexandre.torgue@...s.st.com, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, horms@...nel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	maxime.chevallier@...tlin.com, mcoquelin.stm32@...il.com,
	netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH net v2] net: stmmac: fix transmit queue timed out after
 resume

On Wed, Jan 14, 2026 at 07:00:31PM +0800, Tao Wang wrote:
> after resume dev_watchdog() message:
> "NETDEV WATCHDOG: CPU: x: transmit queue x timed out xx ms"
> 
> The trigging scenario is as follows:
> When the TSO function sets tx_skbuff_dma[tx_q->cur_tx].last_segment = true,
>  and the last_segment value is not cleared in stmmac_free_tx_buffer after
>  resume, restarting TSO transmission may incorrectly use
> tx_q->tx_skbuff_dma[first_entry].last_segment = true for a new TSO packet.
> 
> When the tx queue has timed out, and the emac TX descriptor is as follows:
> eth0: 221 [0x0000000876d10dd0]: 0x73660cbe 0x8 0x42 0xb04416a0
> eth0: 222 [0x0000000876d10de0]: 0x77731d40 0x8 0x16a0 0x90000000
> 
> Descriptor 221 is the TSO header, and descriptor 222 is the TSO payload.
> In the tdes3 (0xb04416a0), bit 29 (first descriptor) and bit 28
> (last descriptor) of the TSO packet 221 DMA descriptor cannot both be
> set to 1 simultaneously. Since descriptor 222 is the actual last
> descriptor, failing to set it properly will cause the EMAC DMA to stop
> and hang.
> 
> To solve the issue, set last_segment to false in stmmac_free_tx_buffer:
> tx_q->tx_skbuff_dma[i].last_segment = false.  Do not use the last_segment
>  default value and set last_segment to false in stmmac_tso_xmit. This
> will prevent similar issues from occurring in the future.

While I agree with the change for stmmac_tso_xmit(), please explain why
the change in stmmac_free_tx_buffer() is necessary.

It seems to me that if this is missing in stmmac_free_tx_buffer(), the
driver should have more problems than just TSO.

-- 
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