[PATCH] 9p/trans_fd: Fix concurrency del of req_list in p9_fd_cancelled/p9_read_work

[Wang Hai]

p9_read_work and p9_fd_cancelled may be called concurrently.
Before list_del(&m->rreq->req_list) in p9_read_work is called,
the req->req_list may have been deleted in p9_fd_cancelled.
We can fix it by setting req->status to REQ_STATUS_FLSHD after
list_del(&req->req_list) in p9_fd_cancelled.

Before list_del(&req->req_list) in p9_fd_cancelled is called,
the req->req_list may have been deleted in p9_read_work.
We should return when req->status = REQ_STATUS_RCVD which means
we just received a response for oldreq, so we need do nothing
in p9_fd_cancelled.

Fixes: 60ff779c4abb ("9p: client: remove unused code and any reference to "cancelled" function")
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
---
 net/9p/trans_fd.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index f868cf6fba79..a563699629cb 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -718,11 +718,18 @@ static int p9_fd_cancelled(struct p9_client *client, struct p9_req_t *req)
 {
 	p9_debug(P9_DEBUG_TRANS, "client %p req %p\n", client, req);
 
-	/* we haven't received a response for oldreq,
-	 * remove it from the list.
+	/* If req->status == REQ_STATUS_RCVD, it means we just received a
+	 * response for oldreq, we need do nothing here. Else, remove it from
+	 * the list.
 	 */
 	spin_lock(&client->lock);
+	if (req->status == REQ_STATUS_RCVD) {
+		spin_unlock(&client->lock);
+		return 0;
+	}
+
 	list_del(&req->req_list);
+	req->status = REQ_STATUS_FLSHD;
 	spin_unlock(&client->lock);
 	p9_req_put(req);
 
-- 
2.17.1