From: Xie He <xie.he.0141@gmail.com> [ Upstream commit 1fef73597fa545c35fddc953979013882fbd4e55 ] ppp_cp_event is called directly or indirectly by ppp_rx with "ppp->lock" held. It may call mod_timer to add a new timer. However, at the same time ppp_timer may be already running and waiting for "ppp->lock". In this case, there's no need for ppp_timer to continue running and it can just exit. If we let ppp_timer continue running, it may call add_timer. This causes kernel panic because add_timer can't be called with a timer pending. This patch fixes this problem. Fixes: e022c2f07ae5 ("WAN: new synchronous PPP implementation for generic HDLC.") Cc: Krzysztof Halasa <khc@pm.waw.pl> Signed-off-by: Xie He <xie.he.0141@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- drivers/net/wan/hdlc_ppp.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c index 20d9b6585fba..d67623d61dc4 100644 --- a/drivers/net/wan/hdlc_ppp.c +++ b/drivers/net/wan/hdlc_ppp.c @@ -572,6 +572,13 @@ static void ppp_timer(struct timer_list *t) unsigned long flags; spin_lock_irqsave(&ppp->lock, flags); + /* mod_timer could be called after we entered this function but + * before we got the lock. + */ + if (timer_pending(&proto->timer)) { + spin_unlock_irqrestore(&ppp->lock, flags); + return; + } switch (proto->state) { case STOPPING: case REQ_SENT: -- 2.25.1