Re: [PATCH net v2] net/smc: fix NULL sndbuf_desc in smc_cdc_tx_handler()

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On 08.03.23 09:17, D. Wythe wrote:
From: "D. Wythe" <alibuda@xxxxxxxxxxxxxxxxx>

When performing a stress test on SMC-R by rmmod mlx5_ib driver
during the wrk/nginx test, we found that there is a probability
of triggering a panic while terminating all link groups.

This issue dues to the race between smc_smcr_terminate_all()
and smc_buf_create().

			smc_smcr_terminate_all

smc_buf_create
/* init */
conn->sndbuf_desc = NULL;
...

			__smc_lgr_terminate
				smc_conn_kill
					smc_close_abort
						smc_cdc_get_slot_and_msg_send

			__softirqentry_text_start
				smc_wr_tx_process_cqe
					smc_cdc_tx_handler
						READ(conn->sndbuf_desc->len);
						/* panic dues to NULL sndbuf_desc */

conn->sndbuf_desc = xxx;

This patch tries to fix the issue by always to check the sndbuf_desc
before send any cdc msg, to make sure that no null pointer is
seen during cqe processing.

Fixes: 0b29ec643613 ("net/smc: immediate termination for SMCR link groups")
Signed-off-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>


Thanks for the fix!

Reviewed-by: Wenjia Zhang <wenjia@xxxxxxxxxxxxx>

v2 -> v1: change retval from EINVAL to ENOBUFS

---
  net/smc/smc_cdc.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
index 53f63bf..89105e9 100644
--- a/net/smc/smc_cdc.c
+++ b/net/smc/smc_cdc.c
@@ -114,6 +114,9 @@ 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++;



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