netdev - Re: Fw: [Bug 86851] New: Reproducible panic on heavy UDP traffic

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Message-ID: <1414370826.16231.1.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 26 Oct 2014 17:47:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nikolay Aleksandrov <nikolay@...hat.com>
Cc:	Florian Westphal <fw@...len.de>,
	Stephen Hemminger <stephen@...workplumber.org>,
	netdev@...r.kernel.org
Subject: Re: Fw: [Bug 86851] New: Reproducible panic on heavy UDP traffic

On Mon, 2014-10-27 at 00:28 +0100, Nikolay Aleksandrov wrote:

> 
> Thanks for CCing me.
> I'll dig in the code tomorrow but my first thought when I saw this was
> could it be possible that we have a race condition between
> ip_frag_queue() and inet_frag_evict(), more precisely between the
> ipq_kill() calls from ip_frag_queue and inet_frag_evict since the frag
> could be found before we have entered the evictor which then can add it to
> its expire list but the ipq_kill() from ip_frag_queue() can do a list_del
> after we release the chain lock in the evictor so we may end up like this ?

Yes, either we use hlist_del_init() but loose poison aid, or test if
frag was evicted :

Not sure about refcount.

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 9eb89f3f0ee4..894ec30c5896 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -285,7 +285,8 @@ static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
 	struct inet_frag_bucket *hb;
 
 	hb = get_frag_bucket_locked(fq, f);
-	hlist_del(&fq->list);
+	if (!(fq->flags & INET_FRAG_EVICTED))
+		hlist_del(&fq->list);
 	spin_unlock(&hb->chain_lock);
 }
 


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