Messages in this thread Patch in this message |  | | From | Bjorn Andersson <> | Subject | [PATCH v3 4/5] net: qrtr: Make qrtr_port_lookup() use RCU | Date | Mon, 6 Jan 2020 21:47:12 -0800 |
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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().
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org> ---
Changes since v2: - None
net/qrtr/qrtr.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c index c2bbfa7ec6e2..aae24c1d8531 100644 --- a/net/qrtr/qrtr.c +++ b/net/qrtr/qrtr.c @@ -641,11 +641,11 @@ 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; } @@ -687,6 +687,10 @@ 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. -- 2.24.0
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