From: Logan Gunthorpe <logang@xxxxxxxxxxxx> [ Upstream commit dae7a589c18a4d979d5f14b09374e871b995ceb1 ] 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 <logang@xxxxxxxxxxxx> Link: https://lore.kernel.org/r/20191216190120.21374-2-logang@xxxxxxxxxxxx Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/dma/dmaengine.c | 4 +++- include/linux/dmaengine.h | 2 ++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index f1a441ab395d7..8a52a5efee4f5 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -190,7 +190,7 @@ __dma_device_satisfies_mask(struct dma_device *device, static struct module *dma_chan_to_owner(struct dma_chan *chan) { - return chan->device->dev->driver->owner; + return chan->device->owner; } /** @@ -923,6 +923,8 @@ int dma_async_device_register(struct dma_device *device) return -EIO; } + device->owner = device->dev->driver->owner; + if (dma_has_cap(DMA_MEMCPY, device->cap_mask) && !device->device_prep_dma_memcpy) { dev_err(device->dev, "Device claims capability %s, but op is not defined\n", diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h index 0647f436f88c2..50128c36f0b48 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -686,6 +686,7 @@ struct dma_filter { * @fill_align: alignment shift for memset operations * @dev_id: unique device ID * @dev: struct device reference for dma mapping api + * @owner: owner module (automatically set based on the provided dev) * @src_addr_widths: bit mask of src addr widths the device supports * Width is specified in bytes, e.g. for a device supporting * a width of 4 the mask should have BIT(4) set. @@ -749,6 +750,7 @@ struct dma_device { int dev_id; struct device *dev; + struct module *owner; u32 src_addr_widths; u32 dst_addr_widths; -- 2.20.1
