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:
    rchan = &dmac->channels[i]
    chan = &rchan->chan
    chan->device = &dmac->engine    rcar_dmac_isr_channel
  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?

Thank you for your time.

-- Anton Volkov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org
e-mail: avol...@ispras.ru

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