Re: [PATCH net v3] net: thunderx: avoid direct MTU assignment after WRITE_ONCE()

[Jacob Keller <jacob.e.keller@intel.com>]

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On 7/6/2025 12:43 PM, Alok Tiwari wrote:
> The current logic in nicvf_change_mtu() writes the new MTU to
> netdev->mtu using WRITE_ONCE() before verifying if the hardware
> update succeeds. However on hardware update failure, it attempts
> to revert to the original MTU using a direct assignment
> (netdev->mtu = orig_mtu)
> which violates the intended of WRITE_ONCE protection introduced in
> commit 1eb2cded45b3 ("net: annotate writes on dev->mtu from
> ndo_change_mtu()")
> 
> Additionally, WRITE_ONCE(netdev->mtu, new_mtu) is unnecessarily
> performed even when the device is not running.
> 
> Fix this by:
>   Only writing netdev->mtu after successfully updating the hardware.
>   Skipping hardware update when the device is down, and setting MTU
>   directly. Remove unused variable orig_mtu.
> 
> This ensures that all writes to netdev->mtu are consistent with
> WRITE_ONCE expectations and avoids unintended state corruption
> on failure paths.
> 
> Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
> ---
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

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