netdev - [net-next PATCH 1/3] net: frag, avoid several CPUs grabbing same frag queue during LRU evictor loop

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Date:	Wed, 27 Mar 2013 16:55:25 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
	Florian Westphal <fw@...len.de>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: [net-next PATCH 1/3] net: frag,
	avoid several CPUs grabbing same frag queue during LRU evictor loop

The LRU list is protected by its own lock, since commit 3ef0eb0db4
(net: frag, move LRU list maintenance outside of rwlock), and
no-longer by a read_lock.

This makes it possible, to remove the inet_frag_queue, which is about
to be "evicted", from the LRU list head.  This avoids the problem, of
several CPUs grabbing the same frag queue.

Note, cannot remove the inet_frag_lru_del() call in fq_unlink()
called by inet_frag_kill(), because inet_frag_kill() is also used in
other situations.  Thus, we use list_del_init() to allow this
double list_del to work.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---

 net/ipv4/inet_fragment.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 2bff045..8ba548a 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -204,6 +204,9 @@ int inet_frag_evictor(struct netns_frags *nf, struct inet_frags *f, bool force)
 		q = list_first_entry(&nf->lru_list,
 				struct inet_frag_queue, lru_list);
 		atomic_inc(&q->refcnt);
+		/* Remove q from list to avoid several CPUs grabbing it */
+		list_del_init(&q->lru_list);
+
 		spin_unlock(&nf->lru_lock);
 
 		spin_lock(&q->lock);

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