netdev - [PATCH 10/11] arch: xtensa: platforms: Fix deadlock in iss_net

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Message-Id: <9867ac04591f1d30b2471cea1b091134f812fd60.1649310812.git.duoming@zju.edu.cn>
Date:   Thu,  7 Apr 2022 14:37:26 +0800
From:   Duoming Zhou <duoming@....edu.cn>
To:     linux-kernel@...r.kernel.org
Cc:     chris@...kel.net, jcmvbkbc@...il.com, mustafa.ismail@...el.com,
        shiraz.saleem@...el.com, jgg@...pe.ca, wg@...ndegger.com,
        mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, jes@...ined-monkey.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        alexander.deucher@....com, linux-xtensa@...ux-xtensa.org,
        linux-rdma@...r.kernel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-hippi@...site.dk,
        linux-staging@...ts.linux.dev, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org, Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH 10/11] arch: xtensa: platforms: Fix deadlock in iss_net_close()

There is a deadlock in iss_net_close(), which is shown
below:

   (Thread 1)              |      (Thread 2)
                           | iss_net_open()
iss_net_close()            |  mod_timer()
 spin_lock_bh() //(1)      |  (wait a time)
 ...                       | iss_net_timer()
 del_timer_sync()          |  spin_lock() //(2)
 (wait timer to stop)      |  ...

We hold lp->lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler
also need lp->lock in position (2) of thread 2. As a result,
iss_net_close() will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_bh(), which could let timer handler to obtain
the needed lock.

Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 arch/xtensa/platforms/iss/network.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/xtensa/platforms/iss/network.c b/arch/xtensa/platforms/iss/network.c
index be3aaaad8be..48340f17e39 100644
--- a/arch/xtensa/platforms/iss/network.c
+++ b/arch/xtensa/platforms/iss/network.c
@@ -403,7 +403,9 @@ static int iss_net_close(struct net_device *dev)
 	list_del(&opened);
 	spin_unlock(&opened_lock);
 
+	spin_unlock_bh(&lp->lock);
 	del_timer_sync(&lp->timer);
+	spin_lock_bh(&lp->lock);
 
 	lp->tp.close(lp);
 
-- 
2.17.1