[PATCH v1 5/6] xprtrdma: Fix MR list handling

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

Close some holes introduced by commit 6dc6ec9e04c4 ("xprtrdma: Cache
free MRs in each rpcrdma_req") that could result in list corruption.

In addition, the result that is tabulated in @count is no longer
used, so @count is removed.

Fixes: 6dc6ec9e04c4 ("xprtrdma: Cache free MRs in each rpcrdma_req")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 net/sunrpc/xprtrdma/verbs.c |   41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 3a1a31c..82361e7 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -79,7 +79,6 @@
 static void rpcrdma_reps_destroy(struct rpcrdma_buffer *buf);
 static void rpcrdma_mrs_create(struct rpcrdma_xprt *r_xprt);
 static void rpcrdma_mrs_destroy(struct rpcrdma_buffer *buf);
-static void rpcrdma_mr_free(struct rpcrdma_mr *mr);
 static struct rpcrdma_regbuf *
 rpcrdma_regbuf_alloc(size_t size, enum dma_data_direction direction,
 		     gfp_t flags);
@@ -966,7 +965,7 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_xprt *r_xprt)
 		mr->mr_xprt = r_xprt;
 
 		spin_lock(&buf->rb_lock);
-		list_add(&mr->mr_list, &buf->rb_mrs);
+		rpcrdma_mr_push(mr, &buf->rb_mrs);
 		list_add(&mr->mr_all, &buf->rb_all_mrs);
 		spin_unlock(&buf->rb_lock);
 	}
@@ -1183,10 +1182,19 @@ int rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
  */
 void rpcrdma_req_destroy(struct rpcrdma_req *req)
 {
+	struct rpcrdma_mr *mr;
+
 	list_del(&req->rl_all);
 
-	while (!list_empty(&req->rl_free_mrs))
-		rpcrdma_mr_free(rpcrdma_mr_pop(&req->rl_free_mrs));
+	while ((mr = rpcrdma_mr_pop(&req->rl_free_mrs))) {
+		struct rpcrdma_buffer *buf = &mr->mr_xprt->rx_buf;
+
+		spin_lock(&buf->rb_lock);
+		list_del(&mr->mr_all);
+		spin_unlock(&buf->rb_lock);
+
+		frwr_release_mr(mr);
+	}
 
 	rpcrdma_regbuf_free(req->rl_recvbuf);
 	rpcrdma_regbuf_free(req->rl_sendbuf);
@@ -1194,24 +1202,28 @@ void rpcrdma_req_destroy(struct rpcrdma_req *req)
 	kfree(req);
 }
 
-static void
-rpcrdma_mrs_destroy(struct rpcrdma_buffer *buf)
+/**
+ * rpcrdma_mrs_destroy - Release all of a transport's MRs
+ * @buf: controlling buffer instance
+ *
+ * Relies on caller holding the transport send lock to protect
+ * removing mr->mr_list from req->rl_free_mrs safely.
+ */
+static void rpcrdma_mrs_destroy(struct rpcrdma_buffer *buf)
 {
 	struct rpcrdma_xprt *r_xprt = container_of(buf, struct rpcrdma_xprt,
 						   rx_buf);
 	struct rpcrdma_mr *mr;
-	unsigned int count;
 
-	count = 0;
 	spin_lock(&buf->rb_lock);
 	while ((mr = list_first_entry_or_null(&buf->rb_all_mrs,
 					      struct rpcrdma_mr,
 					      mr_all)) != NULL) {
+		list_del(&mr->mr_list);
 		list_del(&mr->mr_all);
 		spin_unlock(&buf->rb_lock);
 
 		frwr_release_mr(mr);
-		count++;
 		spin_lock(&buf->rb_lock);
 	}
 	spin_unlock(&buf->rb_lock);
@@ -1284,17 +1296,6 @@ void rpcrdma_mr_put(struct rpcrdma_mr *mr)
 	rpcrdma_mr_push(mr, &mr->mr_req->rl_free_mrs);
 }
 
-static void rpcrdma_mr_free(struct rpcrdma_mr *mr)
-{
-	struct rpcrdma_xprt *r_xprt = mr->mr_xprt;
-	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-
-	mr->mr_req = NULL;
-	spin_lock(&buf->rb_lock);
-	rpcrdma_mr_push(mr, &buf->rb_mrs);
-	spin_unlock(&buf->rb_lock);
-}
-
 /**
  * rpcrdma_buffer_get - Get a request buffer
  * @buffers: Buffer pool from which to obtain a buffer