netdev - Re: [PATCH net] ppp: fix xmit recursion detection on ppp channels

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Date:   Tue, 8 Aug 2017 15:58:27 +0200
From:   Guillaume Nault <g.nault@...halink.fr>
To:     Gao Feng <gfree.wind@....163.com>
Cc:     netdev@...r.kernel.org, Liu Jianying <jianying.liu@...ai8.com>,
        David Miller <davem@...emloft.net>, linux-ppp@...r.kernel.org,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH net] ppp: fix xmit recursion detection on ppp channels

On Tue, Aug 08, 2017 at 09:16:33PM +0800, Gao Feng wrote:
> At 2017-08-08 17:43:24, "Guillaume Nault" <g.nault@...halink.fr> wrote:
> >--- a/drivers/net/ppp/ppp_generic.c
> >+++ b/drivers/net/ppp/ppp_generic.c
> >@@ -1915,21 +1915,23 @@ static void __ppp_channel_push(struct channel *pch)
> > 	spin_unlock(&pch->downl);
> > 	/* see if there is anything from the attached unit to be sent */
> > 	if (skb_queue_empty(&pch->file.xq)) {
> >-		read_lock(&pch->upl);
> > 		ppp = pch->ppp;
> > 		if (ppp)
> >-			ppp_xmit_process(ppp);
> >-		read_unlock(&pch->upl);
> >+			__ppp_xmit_process(ppp);
> > 	}
> > }
> > 
> > static void ppp_channel_push(struct channel *pch)
> > {
> >-	local_bh_disable();
> >-
> >-	__ppp_channel_push(pch);
> >-
> >-	local_bh_enable();
> >+	read_lock_bh(&pch->upl);
> >+	if (pch->ppp) {
> >+		(*this_cpu_ptr(pch->ppp->xmit_recursion))++;
> >+		__ppp_channel_push(pch);
> >+		(*this_cpu_ptr(pch->ppp->xmit_recursion))--;
> >+	} else {
> >+		__ppp_channel_push(pch);
> >+	}
> >+	read_unlock_bh(&pch->upl);
> 
> If invoked read_lock_bh in ppp_channel_push, it would be unnecessary to invoke read_lock(&pch->upl)
> in the __ppp_channel_push.
> 
But this patch does remove read_lock(&pch->upl) from
__ppp_channel_push(). Or have I misunderstood your point?