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    Subject[PATCH 4.14 016/199] PCI/switchtec: Fix init_completion race condition with poll_wait()
    Date
    From: Logan Gunthorpe <logang@deltatee.com>

    [ Upstream commit efbdc769601f4d50018bf7ca50fc9f7c67392ece ]

    The call to init_completion() in mrpc_queue_cmd() can theoretically
    race with the call to poll_wait() in switchtec_dev_poll().

    poll() write()
    switchtec_dev_poll() switchtec_dev_write()
    poll_wait(&s->comp.wait); mrpc_queue_cmd()
    init_completion(&s->comp)
    init_waitqueue_head(&s->comp.wait)

    To my knowledge, no one has hit this bug.

    Fix this by using reinit_completion() instead of init_completion() in
    mrpc_queue_cmd().

    Fixes: 080b47def5e5 ("MicroSemi Switchtec management interface driver")

    Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: Bjorn Helgaas <bhelgaas@google.com>
    Link: https://lkml.kernel.org/r/20200313183608.2646-1-logang@deltatee.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/pci/switch/switchtec.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
    index bf229b442e723..6ef0d4b756f09 100644
    --- a/drivers/pci/switch/switchtec.c
    +++ b/drivers/pci/switch/switchtec.c
    @@ -412,7 +412,7 @@ static int mrpc_queue_cmd(struct switchtec_user *stuser)
    kref_get(&stuser->kref);
    stuser->read_len = sizeof(stuser->data);
    stuser_set_state(stuser, MRPC_QUEUED);
    - init_completion(&stuser->comp);
    + reinit_completion(&stuser->comp);
    list_add_tail(&stuser->list, &stdev->mrpc_queue);

    mrpc_cmd_submit(stdev);
    --
    2.20.1


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