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Thu, 29 May 2025 23:30:15 -0700 (PDT) Received: from gmail.com ([98.97.45.79]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23506bd96eesm21698055ad.73.2025.05.29.23.30.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 May 2025 23:30:14 -0700 (PDT) Date: Thu, 29 May 2025 23:30:11 -0700 From: John Fastabend To: Cong Wang Cc: Zijian Zhang , netdev@vger.kernel.org, bpf@vger.kernel.org, zhoufeng.zf@bytedance.com, jakub@cloudflare.com, Cong Wang Subject: Re: [Patch bpf-next v3 2/4] skmsg: implement slab allocator cache for sk_msg Message-ID: <20250530063011.cqubbcehgnraasmx@gmail.com> References: <20250519203628.203596-1-xiyou.wangcong@gmail.com> <20250519203628.203596-3-xiyou.wangcong@gmail.com> <20250529000348.upto3ztve36ccamv@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On 2025-05-29 11:38:19, Cong Wang wrote: > On Wed, May 28, 2025 at 05:49:22PM -0700, Zijian Zhang wrote: > > On 5/28/25 5:04 PM, John Fastabend wrote: > > > On 2025-05-19 13:36:26, Cong Wang wrote: > > > > From: Zijian Zhang > > > > > > > > Optimizing redirect ingress performance requires frequent allocation and > > > > deallocation of sk_msg structures. Introduce a dedicated kmem_cache for > > > > sk_msg to reduce memory allocation overhead and improve performance. > > > > > > > > Reviewed-by: Cong Wang > > > > Signed-off-by: Zijian Zhang > > > > --- > > > > include/linux/skmsg.h | 21 ++++++++++++--------- > > > > net/core/skmsg.c | 28 +++++++++++++++++++++------- > > > > net/ipv4/tcp_bpf.c | 5 ++--- > > > > 3 files changed, 35 insertions(+), 19 deletions(-) > > > > > > > > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h > > > > index d6f0a8cd73c4..bf28ce9b5fdb 100644 > > > > --- a/include/linux/skmsg.h > > > > +++ b/include/linux/skmsg.h > > > > @@ -121,6 +121,7 @@ struct sk_psock { > > > > struct rcu_work rwork; > > > > }; > > > > +struct sk_msg *sk_msg_alloc(gfp_t gfp); > > > > int sk_msg_expand(struct sock *sk, struct sk_msg *msg, int len, > > > > int elem_first_coalesce); > > > > int sk_msg_clone(struct sock *sk, struct sk_msg *dst, struct sk_msg *src, > > > > @@ -143,6 +144,8 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > > > > int len, int flags); > > > > bool sk_msg_is_readable(struct sock *sk); > > > > +extern struct kmem_cache *sk_msg_cachep; > > > > + > > > > static inline void sk_msg_check_to_free(struct sk_msg *msg, u32 i, u32 bytes) > > > > { > > > > WARN_ON(i == msg->sg.end && bytes); > > > > @@ -319,6 +322,13 @@ static inline void sock_drop(struct sock *sk, struct sk_buff *skb) > > > > kfree_skb(skb); > > > > } > > > > +static inline void kfree_sk_msg(struct sk_msg *msg) > > > > +{ > > > > + if (msg->skb) > > > > + consume_skb(msg->skb); > > > > + kmem_cache_free(sk_msg_cachep, msg); > > > > +} > > > > + > > > > static inline bool sk_psock_queue_msg(struct sk_psock *psock, > > > > struct sk_msg *msg) > > > > { > > > > @@ -330,7 +340,7 @@ static inline bool sk_psock_queue_msg(struct sk_psock *psock, > > > > ret = true; > > > > } else { > > > > sk_msg_free(psock->sk, msg); > > > > - kfree(msg); > > > > + kfree_sk_msg(msg); > > > > > > Isn't this a potential use after free on msg->skb? The sk_msg_free() a > > > line above will consume_skb() if it exists and its not nil set so we would > > > consume_skb() again? > > > > > > > Thanks to sk_msg_free, after consuming the skb, it invokes sk_msg_init > > to make msg->skb NULL to prevent further double free. > > > > To avoid the confusion, we can replace kfree_sk_msg here with > > kmem_cache_free. > > > > Right, the re-initialization in sk_msg_free() is indeed confusing, maybe > it is time to clean up its logic? For example, separate sk_msg_init() > out from sk_msg_free(). > > I can add a separate patch for this in next update, if people prefer. > > Thanks! OK so its not a problem we have the init there. So ACK for this patch. Perhaps a follow up to clean up the different types of 'frees' would be useful. Move into sk_msg_free+kfree_sk_msg into a single call. But, I'm not completely convinced its worth the churn. Acked-by: John Fastabend