net/smc: fix wait on already cleared link

There can be a race between the waiters for a tx work request buffer
and the link down processing that finally clears the link. Although
all waiters are woken up before the link is cleared there might be
waiters which did not yet get back control and are still waiting.
This results in an access to a cleared wait queue head.

Fix this by introducing atomic reference counting around the wait calls,
and wait with the link clear processing until all waiters have finished.
Move the work request layer related calls into smc_wr.c and set the
link state to INACTIVE before calling smcr_link_clear() in
smc_llc_srv_add_link().

Fixes: 15e1b99aadfb ("net/smc: no WR buffer wait for terminating link group")
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 1 deletions

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 289025cd545a..c79361dfcdfb 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -496,7 +496,7 @@ static int smc_tx_rdma_writes(struct smc_connection *conn,
 /* Wakeup sndbuf consumers from any context (IRQ or process)
  * since there is more data to transmit; usable snd_wnd as max transmit
  */
-static int smcr_tx_sndbuf_nonempty(struct smc_connection *conn)
+static int _smcr_tx_sndbuf_nonempty(struct smc_connection *conn)
 {
 	struct smc_cdc_producer_flags *pflags = &conn->local_tx_ctrl.prod_flags;
 	struct smc_link *link = conn->lnk;
@@ -550,6 +550,22 @@ out_unlock:
 	return rc;
 }
 
+static int smcr_tx_sndbuf_nonempty(struct smc_connection *conn)
+{
+	struct smc_link *link = conn->lnk;
+	int rc = -ENOLINK;
+
+	if (!link)
+		return rc;
+
+	atomic_inc(&link->wr_tx_refcnt);
+	if (smc_link_usable(link))
+		rc = _smcr_tx_sndbuf_nonempty(conn);
+	if (atomic_dec_and_test(&link->wr_tx_refcnt))
+		wake_up_all(&link->wr_tx_wait);
+	return rc;
+}
+
 static int smcd_tx_sndbuf_nonempty(struct smc_connection *conn)
 {
 	struct smc_cdc_producer_flags *pflags = &conn->local_tx_ctrl.prod_flags;