blob: 330ab5f62cf6a6ded123d647d7669357fc00add3 [file] [log] [blame]
From 8747e5b482d745c1fa6acc4d69b6cec3542a72cd Mon Sep 17 00:00:00 2001
From: Logan Gunthorpe <>
Date: Mon, 16 Dec 2019 12:01:16 -0700
Subject: [PATCH] dmaengine: Store module owner in dma_device struct
commit dae7a589c18a4d979d5f14b09374e871b995ceb1 upstream.
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 <>
Signed-off-by: Vinod Koul <>
Signed-off-by: Paul Gortmaker <>
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 58cbf9fd5a46..dd22dbd0c4ea 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -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;
@@ -913,6 +913,8 @@ 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) {
"Device claims capability %s, but op is not defined\n",
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index bc6c92dacca3..fa3e8f91b3f5 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -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;