linux-kernel - Re: [PATCH] tipc: fix stall during bclink wakeup procedure

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Date:	Wed, 02 Sep 2015 16:27:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	kolmakov.dmitriy@...wei.com
Cc:	jon.maloy@...csson.com, ying.xue@...driver.com,
	tipc-discussion@...ts.sourceforge.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tipc: fix stall during bclink wakeup procedure

From: Kolmakov Dmitriy <kolmakov.dmitriy@...wei.com>
Date: Wed, 2 Sep 2015 15:33:00 +0000

> If an attempt to wake up users of broadcast link is made when there
> is no enough place in send queue than it may hang up inside the
> tipc_sk_rcv() function since the loop breaks only after the wake up
> queue becomes empty. This can lead to complete CPU stall with the
> following message generated by RCU:

I don't understand how it can loop forever.

It should either successfully deliver each packet to the socket,
or respond with a TIPC_ERR_OVERLOAD.

In both cases, the SKB is dequeued from the queue and forward
progress is made.

If there really is a problem somewhere in here, then two things:

1) You need to describe exactly the sequence of tests and conditions
   that lead to the endless loop in this code, because I cannot see
   it.

2) I suspect the fix is more likely to be appropriate in tipc_sk_rcv()
   or similar, rather than creating a dummy queue to workaround it's
   behavior.

Thanks.
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