drivers: usb: host: Fix deadlock in oxu_bus_suspend()

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

   (Thread 1)              |      (Thread 2)
                           | timer_action()
oxu_bus_suspend()          |  mod_timer()
 spin_lock_irq() //(1)     |  (wait a time)
 ...                       | oxu_watchdog()
 del_timer_sync()          |  spin_lock_irq() //(2)
 (wait timer to stop)      |  ...

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

This patch extracts del_timer_sync() from the protection of
spin_lock_irq(), 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/20220417120305.64577-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/oxu210hp-hcd.c b/drivers/usb/host/oxu210hp-hcd.c
index ddc1558..8b73c61 100644 (file)
--- a/drivers/usb/host/oxu210hp-hcd.c
+++ b/drivers/usb/host/oxu210hp-hcd.c
@@ -3909,8 +3909,10 @@ static int oxu_bus_suspend(struct usb_hcd *hcd)
                }
        }
 
+       spin_unlock_irq(&oxu->lock);
        /* turn off now-idle HC */
        del_timer_sync(&oxu->watchdog);
+       spin_lock_irq(&oxu->lock);
        ehci_halt(oxu);
        hcd->state = HC_STATE_SUSPENDED;