Re: [PATCH net v2] net: Drop the lock in skb_may_tx_timestamp()

[Kurt Kanzenbach <kurt@linutronix.de>]

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On Tue Feb 24 2026, patchwork-bot+netdevbpf@kernel.org wrote:
> Hello:
>
> This patch was applied to netdev/net.git (main)
> by Paolo Abeni <pabeni@redhat.com>:
>
> On Fri, 20 Feb 2026 19:38:58 +0100 you wrote:
>> skb_may_tx_timestamp() may acquire sock::sk_callback_lock. The lock must
>> not be taken in IRQ context, only softirq is okay. A few drivers receive
>> the timestamp via a dedicated interrupt and complete the TX timestamp
>> from that handler. This will lead to a deadlock if the lock is already
>> write-locked on the same CPU.
>> 
>> Taking the lock can be avoided. The socket (pointed by the skb) will
>> remain valid until the skb is released. The ->sk_socket and ->file
>> member will be set to NULL once the user closes the socket which may
>> happen before the timestamp arrives.
>> If we happen to observe the pointer while the socket is closing but
>> before the pointer is set to NULL then we may use it because both
>> pointer (and the file's cred member) are RCU freed.
>> 
>> [...]
>
> Here is the summary with links:
>   - [net,v2] net: Drop the lock in skb_may_tx_timestamp()
>     https://git.kernel.org/netdev/net/c/983512f3a87f
>
> You are awesome, thank you!

Hi maintainers,

thanks for applying the patch.

What's your preferred solution for igb? Can we do the time stamping from
IRQ context now [1] or should we switch to BH workqueue [2]?

Thanks,
Kurt

[1] - https://lore.kernel.org/intel-wired-lan/20260205-igb_irq_ts-v3-1-2efc7bc4b885@linutronix.de/
[2] - https://lore.kernel.org/intel-wired-lan/20260211134436.1e623034@kernel.org/

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