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    SubjectRe: [PATCH 4.4 026/124] iwlwifi: pcie: fix race in Rx buffer allocator
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    On Sat, 2018-08-04 at 11:00 +0200, Greg Kroah-Hartman wrote:
    > 4.4-stable review patch.  If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Shaul Triebitz <shaul.triebitz@intel.com>
    >
    > [ Upstream commit 0f22e40053bd5378ad1e3250e65c574fd61c0cd6 ]
    >
    > Make sure the rx_allocator worker is canceled before running the
    > rx_init routine.  rx_init frees and re-allocates all rxb's pages.  The
    > rx_allocator worker also allocates pages for the used rxb's.  Running
    > rx_init and rx_allocator simultaniously causes a kernel panic.  Fix
    > that by canceling the work in rx_init.
    >
    > Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
    > Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
    > Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > ---
    >  drivers/net/wireless/iwlwifi/pcie/rx.c |    2 ++
    >  1 file changed, 2 insertions(+)
    >
    > --- a/drivers/net/wireless/iwlwifi/pcie/rx.c
    > +++ b/drivers/net/wireless/iwlwifi/pcie/rx.c
    > @@ -713,6 +713,8 @@ int iwl_pcie_rx_init(struct iwl_trans *t
    >   WQ_HIGHPRI | WQ_UNBOUND, 1);
    >   INIT_WORK(&rba->rx_alloc, iwl_pcie_rx_allocator_work);
    >  
    > + cancel_work_sync(&rba->rx_alloc);
    > +
    >   spin_lock(&rba->lock);
    >   atomic_set(&rba->req_pending, 0);
    >   atomic_set(&rba->req_ready, 0);

    This seems to be an incomplete fix. INIT_WORK() will overwrite the
    list pointers in the work item, so there is still a race condition.

    I think that the RX initialisation and reinitialisation/reset cases
    need to be explicitly distinguished. In the initialisation case the
    driver should do only INIT_WORK() and in the reset case it should do
    only cancel_work_sync() (although it would be safe to do INIT_WORK()
    *after* that).

    Ben.

    --
    Ben Hutchings, Software Developer   Codethink Ltd
    https://www.codethink.co.uk/ Dale House, 35 Dale Street
    Manchester, M1 2HF, United Kingdom

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