[PATCH AUTOSEL 4.19 117/252] dmaengine: Store module owner in dma_device struct

[Sasha Levin <sashal@kernel.org>]

From: Logan Gunthorpe <logang@deltatee.com>

[ 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@deltatee.com>
Link: https://lore.kernel.org/r/20191216190120.21374-2-logang@deltatee.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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