RDS/IB: track signaled sends

We're seeing bugs today where IB connection shutdown clears the send
ring while the tasklet is processing completed sends.  Implementation
details cause this to dereference a null pointer.  Shutdown needs to
wait for send completion to stop before tearing down the connection.  We
can't simply wait for the ring to empty because it may contain
unsignaled sends that will never be processed.

This patch tracks the number of signaled sends that we've posted and
waits for them to complete.  It also makes sure that the tasklet has
finished executing.

Signed-off-by: Zach Brown <zach.brown@oracle.com>

1 files changed, 42 insertions, 5 deletions

diff --git a/net/rds/ib_send.c b/net/rds/ib_send.c
index e88cb4af009b..15f75692574c 100644
--- a/net/rds/ib_send.c
+++ b/net/rds/ib_send.c
@@ -220,6 +220,18 @@ void rds_ib_send_clear_ring(struct rds_ib_connection *ic)
 }
 
 /*
+ * The only fast path caller always has a non-zero nr, so we don't
+ * bother testing nr before performing the atomic sub.
+ */
+static void rds_ib_sub_signaled(struct rds_ib_connection *ic, int nr)
+{
+	if ((atomic_sub_return(nr, &ic->i_signaled_sends) == 0) &&
+	    waitqueue_active(&rds_ib_ring_empty_wait))
+		wake_up(&rds_ib_ring_empty_wait);
+	BUG_ON(atomic_read(&ic->i_signaled_sends) < 0);
+}
+
+/*
  * The _oldest/_free ring operations here race cleanly with the alloc/unalloc
  * operations performed in the send path.  As the sender allocs and potentially
  * unallocs the next free entry in the ring it doesn't alter which is
@@ -236,6 +248,7 @@ void rds_ib_send_cq_comp_handler(struct ib_cq *cq, void *context)
 	u32 oldest;
 	u32 i = 0;
 	int ret;
+	int nr_sig = 0;
 
 	rdsdebug("cq %p conn %p\n", cq, conn);
 	rds_ib_stats_inc(s_ib_tx_cq_call);
@@ -262,6 +275,8 @@ void rds_ib_send_cq_comp_handler(struct ib_cq *cq, void *context)
 
 		for (i = 0; i < completed; i++) {
 			send = &ic->i_sends[oldest];
+			if (send->s_wr.send_flags & IB_SEND_SIGNALED)
+				nr_sig++;
 
 			rm = rds_ib_send_unmap_op(ic, send, wc.status);
 
@@ -282,6 +297,8 @@ void rds_ib_send_cq_comp_handler(struct ib_cq *cq, void *context)
 		}
 
 		rds_ib_ring_free(&ic->i_send_ring, completed);
+		rds_ib_sub_signaled(ic, nr_sig);
+		nr_sig = 0;
 
 		if (test_and_clear_bit(RDS_LL_SEND_FULL, &conn->c_flags) ||
 		    test_bit(0, &conn->c_map_queued))
@@ -440,9 +457,9 @@ void rds_ib_advertise_credits(struct rds_connection *conn, unsigned int posted)
 		set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
 }
 
-static inline void rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
-					      struct rds_ib_send_work *send,
-					      bool notify)
+static inline int rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
+					     struct rds_ib_send_work *send,
+					     bool notify)
 {
 	/*
 	 * We want to delay signaling completions just enough to get
@@ -452,7 +469,9 @@ static inline void rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
 	if (ic->i_unsignaled_wrs-- == 0 || notify) {
 		ic->i_unsignaled_wrs = rds_ib_sysctl_max_unsig_wrs;
 		send->s_wr.send_flags |= IB_SEND_SIGNALED;
+		return 1;
 	}
+	return 0;
 }
 
 /*
@@ -488,6 +507,7 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 	int bytes_sent = 0;
 	int ret;
 	int flow_controlled = 0;
+	int nr_sig = 0;
 
 	BUG_ON(off % RDS_FRAG_SIZE);
 	BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));
@@ -645,6 +665,9 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 		if (ic->i_flowctl && flow_controlled && i == (work_alloc-1))
 			send->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;
 
+		if (send->s_wr.send_flags & IB_SEND_SIGNALED)
+			nr_sig++;
+
 		rdsdebug("send %p wr %p num_sge %u next %p\n", send,
 			 &send->s_wr, send->s_wr.num_sge, send->s_wr.next);
 
@@ -689,6 +712,9 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 	if (ic->i_flowctl && i < credit_alloc)
 		rds_ib_send_add_credits(conn, credit_alloc - i);
 
+	if (nr_sig)
+		atomic_add(nr_sig, &ic->i_signaled_sends);
+
 	/* XXX need to worry about failed_wr and partial sends. */
 	failed_wr = &first->s_wr;
 	ret = ib_post_send(ic->i_cm_id->qp, &first->s_wr, &failed_wr);
@@ -699,6 +725,7 @@ int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
 		printk(KERN_WARNING "RDS/IB: ib_post_send to %pI4 "
 		       "returned %d\n", &conn->c_faddr, ret);
 		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
+		rds_ib_sub_signaled(ic, nr_sig);
 		if (prev->s_op) {
 			ic->i_data_op = prev->s_op;
 			prev->s_op = NULL;
@@ -728,6 +755,7 @@ int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
 	u32 pos;
 	u32 work_alloc;
 	int ret;
+	int nr_sig = 0;
 
 	rds_ibdev = ib_get_client_data(ic->i_cm_id->device, &rds_ib_client);
 
@@ -752,7 +780,7 @@ int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
 		send->s_wr.wr.atomic.compare_add = op->op_swap_add;
 		send->s_wr.wr.atomic.swap = 0;
 	}
-	rds_ib_set_wr_signal_state(ic, send, op->op_notify);
+	nr_sig = rds_ib_set_wr_signal_state(ic, send, op->op_notify);
 	send->s_wr.num_sge = 1;
 	send->s_wr.next = NULL;
 	send->s_wr.wr.atomic.remote_addr = op->op_remote_addr;
@@ -778,6 +806,9 @@ int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
 	rdsdebug("rva %Lx rpa %Lx len %u\n", op->op_remote_addr,
 		 send->s_sge[0].addr, send->s_sge[0].length);
 
+	if (nr_sig)
+		atomic_add(nr_sig, &ic->i_signaled_sends);
+
 	failed_wr = &send->s_wr;
 	ret = ib_post_send(ic->i_cm_id->qp, &send->s_wr, &failed_wr);
 	rdsdebug("ic %p send %p (wr %p) ret %d wr %p\n", ic,
@@ -787,6 +818,7 @@ int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
 		printk(KERN_WARNING "RDS/IB: atomic ib_post_send to %pI4 "
 		       "returned %d\n", &conn->c_faddr, ret);
 		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
+		rds_ib_sub_signaled(ic, nr_sig);
 		goto out;
 	}
 
@@ -817,6 +849,7 @@ int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
 	int sent;
 	int ret;
 	int num_sge;
+	int nr_sig = 0;
 
 	/* map the op the first time we see it */
 	if (!op->op_mapped) {
@@ -859,7 +892,7 @@ int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
 		send->s_queued = jiffies;
 		send->s_op = NULL;
 
-		rds_ib_set_wr_signal_state(ic, send, op->op_notify);
+		nr_sig += rds_ib_set_wr_signal_state(ic, send, op->op_notify);
 
 		send->s_wr.opcode = op->op_write ? IB_WR_RDMA_WRITE : IB_WR_RDMA_READ;
 		send->s_wr.wr.rdma.remote_addr = remote_addr;
@@ -910,6 +943,9 @@ int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
 		work_alloc = i;
 	}
 
+	if (nr_sig)
+		atomic_add(nr_sig, &ic->i_signaled_sends);
+
 	failed_wr = &first->s_wr;
 	ret = ib_post_send(ic->i_cm_id->qp, &first->s_wr, &failed_wr);
 	rdsdebug("ic %p first %p (wr %p) ret %d wr %p\n", ic,
@@ -919,6 +955,7 @@ int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
 		printk(KERN_WARNING "RDS/IB: rdma ib_post_send to %pI4 "
 		       "returned %d\n", &conn->c_faddr, ret);
 		rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
+		rds_ib_sub_signaled(ic, nr_sig);
 		goto out;
 	}