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net: qrtr: Make qrtr_port_lookup() use RCU

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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().

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>
This commit is contained in:
Bjorn Andersson 2019-05-30 18:17:52 -07:00 • committed by Chris Lew
commit 8757d5ff17
1 changed files with 6 additions and 2 deletions
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8
net/qrtr/qrtr.c
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@ -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.