[PATCH v4] xprtrdma: Improve locking around rpcrdma_rep destruction

[Chuck Lever <chuck.lever@oracle.com>]

Currently rpcrdma_reps_destroy() assumes that, at transport
tear-down, the content of the rb_free_reps list is the same as the
content of the rb_all_reps list. Although that is usually true,
using the rb_all_reps list should be more reliable because of
the way it's managed. And, rpcrdma_reps_unmap() uses rb_all_reps;
these two functions should both traverse the "all" list.

Ensure that all rpcrdma_reps are always destroyed whether they are
on the rep free list or not.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/verbs.c |   31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

Changes since v3:
- Rename rpcrdma_rep_destroy_locked() as rpcrdma_rep_free()

As far as I can tell, none of the subsequent patches in v3 of the
series need modification, manual or otherwise.

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 1b599a623eea..2bc4589c37ce 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1007,16 +1007,23 @@ struct rpcrdma_rep *rpcrdma_rep_create(struct rpcrdma_xprt *r_xprt,
 	return NULL;
 }
 
-/* No locking needed here. This function is invoked only by the
- * Receive completion handler, or during transport shutdown.
- */
-static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
+static void rpcrdma_rep_free(struct rpcrdma_rep *rep)
 {
-	list_del(&rep->rr_all);
 	rpcrdma_regbuf_free(rep->rr_rdmabuf);
 	kfree(rep);
 }
 
+static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
+{
+	struct rpcrdma_buffer *buf = &rep->rr_rxprt->rx_buf;
+
+	spin_lock(&buf->rb_lock);
+	list_del(&rep->rr_all);
+	spin_unlock(&buf->rb_lock);
+
+	rpcrdma_rep_free(rep);
+}
+
 static struct rpcrdma_rep *rpcrdma_rep_get_locked(struct rpcrdma_buffer *buf)
 {
 	struct llist_node *node;
@@ -1049,8 +1056,18 @@ static void rpcrdma_reps_destroy(struct rpcrdma_buffer *buf)
 {
 	struct rpcrdma_rep *rep;
 
-	while ((rep = rpcrdma_rep_get_locked(buf)) != NULL)
-		rpcrdma_rep_destroy(rep);
+	spin_lock(&buf->rb_lock);
+	while ((rep = list_first_entry_or_null(&buf->rb_all_reps,
+					       struct rpcrdma_rep,
+					       rr_all)) != NULL) {
+		list_del(&rep->rr_all);
+		spin_unlock(&buf->rb_lock);
+
+		rpcrdma_rep_free(rep);
+
+		spin_lock(&buf->rb_lock);
+	}
+	spin_unlock(&buf->rb_lock);
 }
 
 /**