From 382299a020add34cc75ac501bbcb655195c123b8 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Tue, 14 Feb 2017 09:03:51 -0800
Subject: [PATCH] packet: fix races in fanout_add()

commit d199fab63c11998a602205f7ee7ff7c05c97164b upstream.

Multiple threads can call fanout_add() at the same time.

We need to grab fanout_mutex earlier to avoid races that could
lead to one thread freeing po->rollover that was set by another thread.

Do the same in fanout_release(), for peace of mind, and to help us
finding lockdep issues earlier.

Fixes: dc99f600698d ("packet: Add fanout support.")
Fixes: 0648ab70afe6 ("packet: rollover prepare: per-socket state")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
 - No rollover queue stats
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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