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Date:   Mon, 23 Jul 2018 12:59:15 +0200
From:   Florian Westphal <fw@strlen.de>
To:     shaochun chen <cscnull@gmail.com>
Cc:     Florian Westphal <fw@strlen.de>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        David Miller <davem@davemloft.net>,
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        netfilter-devel <netfilter-devel@vger.kernel.org>,
        tom <tom@quantonium.net>, netdev <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] netlink: fix memory leak of dump
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shaochun chen <cscnull@gmail.com> wrote:
> I have a question: we will try_module_get in __netlink_dump_start(),

Thats too late, we release rcu read lock before this, so the module
implementing ->dump might have been removed already.

> but why we need to call try_module_get again in  nft_netlink_dump_start ??

Its the other way around.
This is the first try_module_get; at this point we still hold rcu read
lock.

If nf_tables module is being removed, try_module_get will fail and
we can error out.

If it succeeds, its safe to drop the rcu read lock.