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    Subject[PATCH 5.10 123/172] drivers: usb: host: Fix deadlock in oxu_bus_suspend()
    Date
    From: Duoming Zhou <duoming@zju.edu.cn>

    [ Upstream commit 4d378f2ae58138d4c55684e1d274e7dd94aa6524 ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/usb/host/oxu210hp-hcd.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/usb/host/oxu210hp-hcd.c b/drivers/usb/host/oxu210hp-hcd.c
    index e832909a924f..6df2881cd7b9 100644
    --- a/drivers/usb/host/oxu210hp-hcd.c
    +++ b/drivers/usb/host/oxu210hp-hcd.c
    @@ -3908,8 +3908,10 @@ 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;

    --
    2.35.1


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