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    SubjectRe: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode
    Sorry for delay.

    On Tue, Jun 12, 2018 at 03:25:40PM -0700, David Miller wrote:
    > From: Dean Nelson <dnelson@redhat.com>
    > Date: Mon, 11 Jun 2018 06:22:14 -0500
    >
    > > 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.
    >
    > You're right, my bad.
    >
    > Patch applied.

    Thank you for your time.

    WBR,
    Vadim

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