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Date:   Mon, 7 Nov 2022 19:55:26 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Jacob Keller <jacob.e.keller@intel.com>
Cc:     Leon Romanovsky <leon@kernel.org>,
        "Ruhl, Michael J" <michael.j.ruhl@intel.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@intel.com>,
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        Kees Cook <keescook@chromium.org>,
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        "Brandeburg, Jesse" <jesse.brandeburg@intel.com>,
        "intel-wired-lan@lists.osuosl.org" <intel-wired-lan@lists.osuosl.org>,
        "G, GurucharanX" <gurucharanx.g@intel.com>
Subject: Re: [PATCH net-next 5/6] igb: Do not free q_vector unless new one
 was allocated
Message-ID: <20221107195526.5ef1262e@kernel.org>
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On Mon, 7 Nov 2022 10:35:14 -0800 Jacob Keller wrote:
> > I understand the issue what you are trying to solve, I just don't
> > understand your RCU code. I would expect calls to rcu_dereference()
> > in order to get q_vector and rcu_assign_pointer() to clear
> > adapter->q_vector[v_idx], but igb has none.
> 
> the uses of kfree_rcu were introduced by 5536d2102a2d ("igb: Combine 
> q_vector and ring allocation into a single function")
> 
> The commit doesn't mention switching from kfree to kfree_rcu and I 
> suspect that the igb driver is not actually really using RCU semantics 
> properly.
> 
> The closest explanation is that the get_stats64 function might be 
> accessing the ring and thus needs the RCU grace period.. but I think 
> you're right in that we're missing the necessary RCU access macros.

Alright, expecting a follow up for this.