9P: Fix race between p9_write_work() and p9_fd_request()
Race scenario:
thread A thread B
p9_write_work() p9_fd_request()
if (list_empty
(&m->unsent_req_list))
...
spin_lock(&client->lock);
req->status = REQ_STATUS_UNSENT;
list_add_tail(..., &m->unsent_req_list);
spin_unlock(&client->lock);
....
if (n & POLLOUT &&
!test_and_set_bit(Wworksched, &m->wsched)
schedule_work(&m->wq);
--> not done because Wworksched is set
clear_bit(Wworksched, &m->wsched);
return;
--> nobody will take care of sending the new request.
This is not very likely to happen though, because p9_write_work()
being called with an empty unsent_req_list is not frequent.
But this also means that taking the lock earlier will not be costly.
Signed-off-by: Simon Derr <simon.derr@bull.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index b2c308f..0031a8c 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -453,12 +453,13 @@
}
if (!m->wsize) {
+ spin_lock(&m->client->lock);
if (list_empty(&m->unsent_req_list)) {
clear_bit(Wworksched, &m->wsched);
+ spin_unlock(&m->client->lock);
return;
}
- spin_lock(&m->client->lock);
req = list_entry(m->unsent_req_list.next, struct p9_req_t,
req_list);
req->status = REQ_STATUS_SENT;