From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guillaume Nault Date: Wed, 17 Aug 2016 17:42:19 +0000 Subject: Re: [PATCH v2 1/1] ppp: Fix one deadlock issue of PPP when send frame Message-Id: <20160817174219.y4opmhj4u77m3ufq@alphalink.fr> List-Id: References: <1471347218-24472-1-git-send-email-fgao@ikuai8.com> In-Reply-To: <1471347218-24472-1-git-send-email-fgao@ikuai8.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: fgao@ikuai8.com Cc: paulus@samba.org, linux-ppp@vger.kernel.org, netdev@vger.kernel.org, gfree.wind@gmail.com On Tue, Aug 16, 2016 at 07:33:38PM +0800, fgao@ikuai8.com 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 recursively). > 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 { > |SC_MULTILINK|SC_MP_SHORTSEQ|SC_MP_XSHORTSEQ \ > |SC_COMP_TCP|SC_REJ_COMP_TCP|SC_MUST_COMP) > > +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'?