netdev - Re: [PATCH net 3/5] net/smc: allow cdc msg send rather than drop it with NULL sndbuf

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Date: Thu, 12 Oct 2023 10:49:30 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: Wenjia Zhang <wenjia@...ux.ibm.com>, kgraul@...ux.ibm.com,
 jaka@...ux.ibm.com, wintera@...ux.ibm.com
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
 linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net 3/5] net/smc: allow cdc msg send rather than drop it
 with NULL sndbuf_desc



On 10/12/23 4:37 AM, Wenjia Zhang wrote:
>
>
> On 11.10.23 09:33, D. Wythe wrote:
>> From: "D. Wythe" <alibuda@...ux.alibaba.com>
>>
>> This patch re-fix the issues memtianed by commit 22a825c541d7
>> ("net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()").
>>
>> Blocking sending message do solve the issues though, but it also
>> prevents the peer to receive the final message. Besides, in logic,
>> whether the sndbuf_desc is NULL or not have no impact on the processing
>> of cdc message sending.
>>
> Agree.
>
>> Hence that, this patch allow the cdc message sending but to check the
>> sndbuf_desc with care in smc_cdc_tx_handler().
>>
>> Fixes: 22a825c541d7 ("net/smc: fix NULL sndbuf_desc in 
>> smc_cdc_tx_handler()")
>> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
>> ---
>>   net/smc/smc_cdc.c | 9 ++++-----
>>   1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
>> index 01bdb79..3c06625 100644
>> --- a/net/smc/smc_cdc.c
>> +++ b/net/smc/smc_cdc.c
>> @@ -28,13 +28,15 @@ static void smc_cdc_tx_handler(struct 
>> smc_wr_tx_pend_priv *pnd_snd,
>>   {
>>       struct smc_cdc_tx_pend *cdcpend = (struct smc_cdc_tx_pend 
>> *)pnd_snd;
>>       struct smc_connection *conn = cdcpend->conn;
>> +    struct smc_buf_desc *sndbuf_desc;
>>       struct smc_sock *smc;
>>       int diff;
>>   +    sndbuf_desc = conn->sndbuf_desc;
>>       smc = container_of(conn, struct smc_sock, conn);
>>       bh_lock_sock(&smc->sk);
>> -    if (!wc_status) {
>> -        diff = smc_curs_diff(cdcpend->conn->sndbuf_desc->len,
>> +    if (!wc_status && sndbuf_desc) {
>> +        diff = smc_curs_diff(sndbuf_desc->len,
> How could this guarantee that the sndbuf_desc would not be NULL?
>

It can not guarantee he sndbuf_desc would not be NULL, but it will prevents
the smc_cdc_tx_handler() to access a NULL sndbuf_desc. So that we
can avoid the panic descried in commit 22a825c541d7
("net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()").

>> &cdcpend->conn->tx_curs_fin,
>>                        &cdcpend->cursor);
>>           /* sndbuf_space is decreased in smc_sendmsg */
>> @@ -114,9 +116,6 @@ int smc_cdc_msg_send(struct smc_connection *conn,
>>       union smc_host_cursor cfed;
>>       int rc;
>>   -    if (unlikely(!READ_ONCE(conn->sndbuf_desc)))
>> -        return -ENOBUFS;
>> -
>>       smc_cdc_add_pending_send(conn, pend);
>>         conn->tx_cdc_seq++;