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[104.188.17.28]) by smtp.gmail.com with ESMTPSA id k21sm67129177pfa.63.2020.01.06.21.48.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jan 2020 21:48:00 -0800 (PST) From: Bjorn Andersson To: "David S. Miller" Cc: Arun Kumar Neelakantam , Chris Lew , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org Subject: [PATCH v3 4/5] net: qrtr: Make qrtr_port_lookup() use RCU Date: Mon, 6 Jan 2020 21:47:12 -0800 Message-Id: <20200107054713.3909260-5-bjorn.andersson@linaro.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20200107054713.3909260-1-bjorn.andersson@linaro.org> References: <20200107054713.3909260-1-bjorn.andersson@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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