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From: Guillaume Nault <>
Subject: Re: [PATCH v2 1/1] ppp: Fix one deadlock issue of PPP when send frame
Date: Wed, 17 Aug 2016 17:42:19 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Aug 16, 2016 at 07:33:38PM +0800, wrote:
> From: Gao Feng <>
> PPP channel holds one spinlock before send frame. But the skb may
> select the same PPP channel with wrong route policy. As a result,
> the skb reaches the same channel path. It tries to get the same
> spinlock which is held before. Bang, the deadlock comes out.
Unless I misunderstood the problem you're trying to solve, this patch
doesn't really help: deadlock still occurs if the same IP is used for
L2TP and PPP's peer address.

> Now add one lock owner to avoid it like xmit_lock_owner of
> netdev_queue. Check the lock owner before try to get the spinlock.
> If the current cpu is already the owner, needn't lock again. When
> PPP channel holds the spinlock at the first time, it sets owner
> with current CPU ID.
I think you should forbid lock recursion entirely, and drop the packet
if the owner tries to re-acquire the channel lock. Otherwise you just
move the deadlock down the stack (l2tp_xmit_skb() can't be called

> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index 70cfa06..6909ab1 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -162,6 +162,37 @@ struct ppp {
> +struct chennel_lock {
I guess you meant 'channel_lock'.

> +	spinlock_t lock;
> +	u32 owner;
This field's default value is -1. So why not declaring it as 'int'?

  reply	other threads:[~2016-08-17 17:42 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-16 11:33 [PATCH v2 1/1] ppp: Fix one deadlock issue of PPP when send frame fgao
2016-08-17 17:42 ` Guillaume Nault [this message]
2016-08-18  0:58   ` Feng Gao
2016-08-18 16:13     ` Guillaume Nault
2016-08-18 22:52       ` Feng Gao
2016-08-19 21:57         ` Guillaume Nault

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