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    Subject[PATCH AUTOSEL 5.17 11/60] drivers: staging: rtl8192e: Fix deadlock in rtllib_beacons_stop()
    Date
    From: Duoming Zhou <duoming@zju.edu.cn>

    [ Upstream commit 9b6bdbd9337de3917945847bde262a34a87a6303 ]

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

    (Thread 1) | (Thread 2)
    | rtllib_send_beacon()
    rtllib_beacons_stop() | mod_timer()
    spin_lock_irqsave() //(1) | (wait a time)
    ... | rtllib_send_beacon_cb()
    del_timer_sync() | spin_lock_irqsave() //(2)
    (wait timer to stop) | ...

    We hold ieee->beacon_lock in position (1) of thread 1 and
    use del_timer_sync() to wait timer to stop, but timer handler
    also need ieee->beacon_lock in position (2) of thread 2.
    As a result, rtllib_beacons_stop() 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/20220417141641.124388-1-duoming@zju.edu.cn
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/staging/rtl8192e/rtllib_softmac.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/staging/rtl8192e/rtllib_softmac.c b/drivers/staging/rtl8192e/rtllib_softmac.c
    index 4b6c2295a3cf..b5a38f0a8d79 100644
    --- a/drivers/staging/rtl8192e/rtllib_softmac.c
    +++ b/drivers/staging/rtl8192e/rtllib_softmac.c
    @@ -651,9 +651,9 @@ static void rtllib_beacons_stop(struct rtllib_device *ieee)
    spin_lock_irqsave(&ieee->beacon_lock, flags);

    ieee->beacon_txing = 0;
    - del_timer_sync(&ieee->beacon_timer);

    spin_unlock_irqrestore(&ieee->beacon_lock, flags);
    + del_timer_sync(&ieee->beacon_timer);

    }

    --
    2.35.1
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