netdev - Re: [PATCH net-next v3 1/2] pppoe: remove rwlock usage

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Message-ID: <CANn89i+WjMR7kcGkaQvF5YaCiZxa6txMyQvvVQf8rcU7_u9_JA@mail.gmail.com>
Date: Thu, 28 Aug 2025 00:01:44 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Qingfang Deng <dqfext@...il.com>
Cc: Michal Ostrowski <mostrows@...thlink.net>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/2] pppoe: remove rwlock usage

On Wed, Aug 27, 2025 at 6:20 PM Qingfang Deng <dqfext@...il.com> wrote:
>
> Like ppp_generic.c, convert the PPPoE socket hash table to use RCU for
> lookups and a spinlock for updates. This removes rwlock usage and allows
> lockless readers on the fast path.
>
> - Mark hash table and list pointers as __rcu.
> - Use spin_lock() to protect writers.
> - Readers use rcu_dereference() under rcu_read_lock(). All known callers
>   of get_item() already hold the RCU read lock, so no additional locking
>   is needed.
> - get_item() now uses refcount_inc_not_zero() instead of sock_hold() to
>   safely take a reference. This prevents crashes if a socket is already
>   in the process of being freed (sk_refcnt == 0).
> - Set SOCK_RCU_FREE to defer socket freeing until after an RCU grace
>   period.
> - Move skb_queue_purge() into sk_destruct callback to ensure purge
>   happens after an RCU grace period.
>
> Signed-off-by: Qingfang Deng <dqfext@...il.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@...gle.com>