Commit 8757d5ff authored May 30, 2019 by Bjorn Andersson Committed by Chris Lew Oct 01, 2019

net: qrtr: Make qrtr_port_lookup() use RCU



The important part of qrtr_port_lookup() wrt synchronization is that the
function returns a reference counted struct qrtr_sock, or fail.

As such we need only to ensure that an decrement of the object's
refcount happens inbetween the finding of the object in the idr and
qrtr_port_lookup()'s own increment of the object.

By using RCU and putting a synchronization point after we remove the
mapping from the idr, but before it can be released we achieve this -
with the benefit of not having to hold the mutex in qrtr_port_lookup().

Change-Id: Ia9907a9c97a29e92a92e67afa988207f501a2f48
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Patch-mainline: linux-arm-kernel @ 07/05/19, 23:06
Signed-off-by: Chris Lew <clew@codeaurora.org>

parent 83e68efe

net/qrtr/qrtr.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -639,11 +639,11 @@ static struct qrtr_sock *qrtr_port_lookup(int port)
		if (port == QRTR_PORT_CTRL)
		port = 0;

		mutex_lock(&qrtr_port_lock);
		rcu_read_lock();
		ipc = idr_find(&qrtr_ports, port);
		if (ipc)
		sock_hold(&ipc->sk);
		mutex_unlock(&qrtr_port_lock);
		rcu_read_unlock();

		return ipc;
		}
		@@ -685,6 +685,10 @@ static void qrtr_port_remove(struct qrtr_sock *ipc)
		mutex_lock(&qrtr_port_lock);
		idr_remove(&qrtr_ports, port);
		mutex_unlock(&qrtr_port_lock);

		/* Ensure that if qrtr_port_lookup() did enter the RCU read section we
		* wait for it to up increment the refcount */
		synchronize_rcu();
		}

		/* Assign port number to socket.