Subject: Re: [PATCH v3 1/1] net:rds: Fix possible deadlock in rds_message_put

From: Zhu Yanjun <[email-masked]>
Date: Thu, 8 Feb 2024 15:37:18 +0800

在 2024/2/8 7:38, [email-masked] 写道:
> From: Allison Henderson <[email-masked]>
> 
> Functions rds_still_queued and rds_clear_recv_queue lock a given socket
> in order to safely iterate over the incoming rds messages. However
> calling rds_inc_put while under this lock creates a potential deadlock.
> rds_inc_put may eventually call rds_message_purge, which will lock
> m_rs_lock. This is the incorrect locking order since m_rs_lock is
> meant to be locked before the socket. To fix this, we move the message
> item to a local list or variable that wont need rs_recv_lock protection.
> Then we can safely call rds_inc_put on any item stored locally after
> rs_recv_lock is released.
> 
> Fixes: bdbe6fbc6a2f (RDS: recv.c)

A trivial problem,
Based on the file 
https://www.kernel.org/doc/Documentation/process/submitting-patches.rst, 
Fixes tag should be the following?

Fixes: bdbe6fbc6a2f ("RDS: recv.c")

Thanks,
Zhu Yanjun

> Reported-by: [email-masked]
> Reported-by: [email-masked]
> 
> Signed-off-by: Allison Henderson <[email-masked]>
> ---
>   net/rds/recv.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/net/rds/recv.c b/net/rds/recv.c
> index c71b923764fd..5627f80013f8 100644
> --- a/net/rds/recv.c
> +++ b/net/rds/recv.c
> @@ -425,6 +425,7 @@ static int rds_still_queued(struct rds_sock *rs, struct rds_incoming *inc,
>   	struct sock *sk = rds_rs_to_sk(rs);
>   	int ret = 0;
>   	unsigned long flags;
> +	struct rds_incoming *to_drop = NULL;
>   
>   	write_lock_irqsave(&rs->rs_recv_lock, flags);
>   	if (!list_empty(&inc->i_item)) {
> @@ -435,11 +436,14 @@ static int rds_still_queued(struct rds_sock *rs, struct rds_incoming *inc,
>   					      -be32_to_cpu(inc->i_hdr.h_len),
>   					      inc->i_hdr.h_dport);
>   			list_del_init(&inc->i_item);
> -			rds_inc_put(inc);
> +			to_drop = inc;
>   		}
>   	}
>   	write_unlock_irqrestore(&rs->rs_recv_lock, flags);
>   
> +	if (to_drop)
> +		rds_inc_put(to_drop);
> +
>   	rdsdebug("inc %p rs %p still %d dropped %d\n", inc, rs, ret, drop);
>   	return ret;
>   }
> @@ -758,16 +762,21 @@ void rds_clear_recv_queue(struct rds_sock *rs)
>   	struct sock *sk = rds_rs_to_sk(rs);
>   	struct rds_incoming *inc, *tmp;
>   	unsigned long flags;
> +	LIST_HEAD(to_drop);
>   
>   	write_lock_irqsave(&rs->rs_recv_lock, flags);
>   	list_for_each_entry_safe(inc, tmp, &rs->rs_recv_queue, i_item) {
>   		rds_recv_rcvbuf_delta(rs, sk, inc->i_conn->c_lcong,
>   				      -be32_to_cpu(inc->i_hdr.h_len),
>   				      inc->i_hdr.h_dport);
> +		list_move(&inc->i_item, &to_drop);
> +	}
> +	write_unlock_irqrestore(&rs->rs_recv_lock, flags);
> +
> +	list_for_each_entry_safe(inc, tmp, &to_drop, i_item) {
>   		list_del_init(&inc->i_item);
>   		rds_inc_put(inc);
>   	}
> -	write_unlock_irqrestore(&rs->rs_recv_lock, flags);
>   }
>   
>   /*