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    SubjectRe: Possible null pointer dereference in rcar-dmac.ko
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    Hi Anton

    # add Laurent

    > While searching for races in the Linux kernel I've come across
    > "drivers/dma/sh/rcar-dmac.ko" module. Here is a question that I came
    > up with while analyzing results. Lines are given using the info from
    > Linux v4.12.
    >
    > Consider the following case:
    >
    > Thread 1: Thread 2:
    > rcar_dmac_probe
    > ->rcar_dmac_chan_probe
    > (&dmac->channels[i])
    > rchan = &dmac->channels[i]
    > chan = &rchan->chan
    > devm_request_threaded_irq(rchan)
    > chan->device = &dmac->engine rcar_dmac_isr_channel
    > ->rcar_dmac_isr_transfer_end(chan)
    > ->rcar_dmac_chan_start_xfer(chan)
    > engine->dev = &pdev->dev; <READ chan->chan.device->dev>
    > (rcar-dmac.c: line 1828) (rcar-dmac.c: line 351)
    >
    > As far as I understand engine->dev is NULL before its initialization
    > in probe. Thus there might be a NULL pointer dereference in
    > rcar_dmac_chan_start_xfer while accessing chan->chan.device->dev which
    > is equal to (&dmac->engine)->dev. Is this possible from your point of
    > view?

    Very rare case, but not impossible (?).
    I think these engine->xxx initialize should be done before
    of_dma_controller_register();
    engine.channels is initialized independently somehow...

    Best regards
    ---
    Kuninori Morimoto

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