netdev - [PATCH net] r8152: Re-order napi_disable in rtl8152

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Message-Id: <20191120194020.8796-1-pmalani@chromium.org>
Date:   Wed, 20 Nov 2019 11:40:21 -0800
From:   Prashant Malani <pmalani@...omium.org>
To:     hayeswang@...ltek.com
Cc:     grundler@...omium.org, netdev@...r.kernel.org,
        nic_swsd@...ltek.com, Prashant Malani <pmalani@...omium.org>
Subject: [PATCH net] r8152: Re-order napi_disable in rtl8152_close

Both rtl_work_func_t() and rtl8152_close() call napi_disable().
Since the two calls aren't protected by a lock, if the close
function starts executing before the work function, we can get into a
situation where the napi_disable() function is called twice in
succession (first by rtl8152_close(), then by set_carrier()).

In such a situation, the second call would loop indefinitely, since
rtl8152_close() doesn't call napi_enable() to clear the NAPI_STATE_SCHED
bit.

The rtl8152_close() function in turn issues a
cancel_delayed_work_sync(), and so it would wait indefinitely for the
rtl_work_func_t() to complete. Since rtl8152_close() is called by a
process holding rtnl_lock() which is requested by other processes, this
eventually leads to a system deadlock and crash.

Re-order the napi_disable() call to occur after the work function
disabling and urb cancellation calls are issued.

Change-Id: I6ef0b703fc214998a037a68f722f784e1d07815e
Reported-by: http://crbug.com/1017928
Signed-off-by: Prashant Malani <pmalani@...omium.org>
---
 drivers/net/usb/r8152.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index d4a95b50bda6b..4d34c01826f30 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -4283,10 +4283,10 @@ static int rtl8152_close(struct net_device *netdev)
 	unregister_pm_notifier(&tp->pm_notifier);
 #endif
 	tasklet_disable(&tp->tx_tl);
-	napi_disable(&tp->napi);
 	clear_bit(WORK_ENABLE, &tp->flags);
 	usb_kill_urb(tp->intr_urb);
 	cancel_delayed_work_sync(&tp->schedule);
+	napi_disable(&tp->napi);
 	netif_stop_queue(netdev);

 	res = usb_autopm_get_interface(tp->intf);
-- 
2.24.0.432.g9d3f5f5b63-goog