Commit dae7a589 authored Dec 16, 2019 by Logan Gunthorpe Committed by Vinod Koul Dec 24, 2019

dmaengine: Store module owner in dma_device struct

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@deltatee.com>
Link: https://lore.kernel.org/r/20191216190120.21374-2-logang@deltatee.com

Signed-off-by: Vinod Koul <vkoul@kernel.org>

parent 20f5a659

drivers/dma/dmaengine.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -179,7 +179,7 @@ __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;
		}

		/**
		@@ -919,6 +919,8 @@ 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",

include/linux/dmaengine.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -674,6 +674,7 @@ 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.
		@@ -737,6 +738,7 @@ struct dma_device {

		int dev_id;
		struct device *dev;
		struct module *owner;

		u32 src_addr_widths;
		u32 dst_addr_widths;

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