drivers: net: hippi: Fix deadlock in rr_close()

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>

diff --git a/drivers/net/hippi/rrunner.c b/drivers/net/hippi/rrunner.c
index 16105292b140bbc44c97cd9370c4f6db163dea2d..74e845fa2e07ed8e2430c57c2d24b830be361be8 100644 (file)
--- a/drivers/net/hippi/rrunner.c
+++ b/drivers/net/hippi/rrunner.c
@@ -1355,7 +1355,9 @@ 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);