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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Duoming Zhou <duoming@zju.edu.cn>, Paolo Abeni <pabeni@redhat.com>,
        Sasha Levin <sashal@kernel.org>, jes@trained-monkey.org,
        davem@davemloft.net, kuba@kernel.org, linux-hippi@sunsite.dk,
        netdev@vger.kernel.org
Subject: [PATCH AUTOSEL 4.9 2/3] drivers: net: hippi: Fix deadlock in rr_close()
Date:   Tue, 26 Apr 2022 15:03:02 -0400
Message-Id: <20220426190304.2351976-2-sashal@kernel.org>
In-Reply-To: <20220426190304.2351976-1-sashal@kernel.org>
References: <20220426190304.2351976-1-sashal@kernel.org>
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From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit bc6de2878429e85c1f1afaa566f7b5abb2243eef ]

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

   (Thread 1)                |      (Thread 2)
                             | rr_open()
rr_close()                   |  add_timer()
 spin_lock_irqsave() //(1)   |  (wait a time)
 ...                         | rr_timer()
 del_timer_sync()            |  spin_lock_irqsave() //(2)
 (wait timer to stop)        |  ...

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

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

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220417125519.82618-1-duoming@zju.edu.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/hippi/rrunner.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/hippi/rrunner.c b/drivers/net/hippi/rrunner.c
index 6f3519123eb6..0e1a422d9567 100644
--- a/drivers/net/hippi/rrunner.c
+++ b/drivers/net/hippi/rrunner.c
@@ -1354,7 +1354,9 @@ static int rr_close(struct net_device *dev)
 
 	rrpriv->fw_running = 0;
 
+	spin_unlock_irqrestore(&rrpriv->lock, flags);
 	del_timer_sync(&rrpriv->timer);
+	spin_lock_irqsave(&rrpriv->lock, flags);
 
 	writel(0, &regs->TxPi);
 	writel(0, &regs->IpRxPi);
-- 
2.35.1