dma_chan_to_owner() dereferences the driver from the struct device to
obtain the owner and call module_[get|put](). However, if the backing
device is unbound before the dma_device is unregistered, the driver
will be cleared and this will cause a NULL pointer dereference.
Instead, store a pointer to the owner module in the dma_device struct
so the module reference can be properly put when the channel is put, even
if the backing device was destroyed first.
This change helps to support a safer unbind of DMA engines.
If the dma_device is unregistered in the driver's remove function,
there's no guarantee that there are no existing clients and a users
action may trigger the WARN_ONCE in dma_async_device_unregister()
which is unlikely to leave the system in a consistent state.
Instead, a better approach is to allow the backing driver to go away
and fail any subsequent requests to it.
Signed-off-by: Logan Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>
Logan Gunthorpe
dae7a589c1