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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>
This commit is contained in:
Logan Gunthorpe 2019-12-16 12:01:16 -07:00 committed by Vinod Koul
parent 20f5a65955
commit dae7a589c1
2 changed files with 5 additions and 1 deletions
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4
drivers/dma/dmaengine.c
View File

@ -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",

2
include/linux/dmaengine.h
View File

@ -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;