From: Dean Nelson <dnelson@redhat.com>
To: David Miller <davem@davemloft.net>, Vadim.Lomovtsev@caviumnetworks.com
Cc: rric@kernel.org, sgoutham@cavium.com,
linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, Vadim.Lomovtsev@cavium.com
Subject: Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode
Date: Mon, 11 Jun 2018 06:22:14 -0500 [thread overview]
Message-ID: <036618ae-887f-44b5-2b39-451b81191cc1@redhat.com> (raw)
In-Reply-To: <20180610.123551.885190586229525170.davem@davemloft.net>
On 06/10/2018 02:35 PM, David Miller wrote:
> From: Vadim Lomovtsev <Vadim.Lomovtsev@caviumnetworks.com>
> Date: Fri, 8 Jun 2018 02:27:59 -0700
>
>> + /* Save message data locally to prevent them from
>> + * being overwritten by next ndo_set_rx_mode call().
>> + */
>> + spin_lock(&nic->rx_mode_wq_lock);
>> + mode = vf_work->mode;
>> + mc = vf_work->mc;
>> + vf_work->mc = NULL;
If I'm reading this code correctly, I believe nic->rx_mode_work.mc will
have been set to NULL before the lock is dropped by
nicvf_set_rx_mode_task() and acquired by nicvf_set_rx_mode().
>> + spin_unlock(&nic->rx_mode_wq_lock);
>
> At the moment you drop this lock, the memory behind 'mc' can be
> freed up by:
>
>> + spin_lock(&nic->rx_mode_wq_lock);
>> + kfree(nic->rx_mode_work.mc);
So the kfree() will be called with a NULL pointer and quickly return.
>
> And you'll crash when you dereference it above via
> __nicvf_set_rx_mode_task().
>
I believe the call to kfree() in nicvf_set_rx_mode() is there to free
up a mc_list that has been allocated by nicvf_set_rx_mode() during a
previous callback to the function, one that has not yet been processed
by nicvf_set_rx_mode_task().
In this way only the last 'unprocessed' callback to nicvf_set_rx_mode()
gets processed should there be multiple callbacks occurring between the
times the nicvf_set_rx_mode_task() runs.
In my testing with this patch, this is what I see happening.
next prev parent reply other threads:[~2018-06-11 11:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-08 9:27 [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode Vadim Lomovtsev
2018-06-10 19:35 ` David Miller
2018-06-11 11:22 ` Dean Nelson [this message]
2018-06-12 22:25 ` David Miller
2018-06-13 9:15 ` Vadim Lomovtsev
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