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Let drivers add their own sysfs > attributes to that device directly, via a new dma_device.chan_groups > field. > > This avoids drivers needing a second, separately-managed kobject to > expose driver-specific attributes. That's a use-after-free issue: > kobject_put() can invoke the ktype's release() and free the structure > embedding dma_chan while the core (or the driver) still expects to > reference it afterward, so avoiding it requires careful ordering and > bookkeeping that's easy to get wrong. The channel's struct device > already has the correct lifetime, and sysfs_create_group() supports > the same named-subdirectory layout (attribute_group.name) that a bare > kobject would provide. > > To let show()/store() callbacks safely recover the struct dma_chan from > the struct device they're attached to without exposing dma_list_mutex > itself to drivers, add a small dma_chan_from_dev_lock() / > dma_chan_from_dev_unlock() pair that take / release the lock, and > wrap them in a dma_chan_from_dev CLASS so callers can write: > > CLASS(dma_chan_from_dev, c)(dev); > if (!c) > return -ENODEV; > > Signed-off-by: Logan Gunthorpe > --- > drivers/dma/dmaengine.c | 27 +++++++++++++++++++++++++++ > drivers/dma/dmaengine.h | 19 +++++++++++++++++++ > include/linux/dmaengine.h | 4 ++++ > 3 files changed, 50 insertions(+) > > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c > index 9049171df857..060a0a482eb3 100644 > --- a/drivers/dma/dmaengine.c > +++ b/drivers/dma/dmaengine.c > @@ -161,6 +161,32 @@ static struct dma_chan *dev_to_dma_chan(struct device *dev) > return chan_dev->chan; > } > > +/** > + * dma_chan_from_dev_lock - take dma_list_mutex and convert a channel's > + * struct device to its dma_chan > + * @dev: the channel's struct device, embedded in struct dma_chan_dev > + * > + * Returns NULL if the channel has already been unregistered. Pairs with > + * dma_chan_from_dev_unlock(); see the dma_chan_from_dev CLASS in > + * drivers/dma/dmaengine.h. > + */ > +struct dma_chan *dma_chan_from_dev_lock(struct device *dev) > +{ > + mutex_lock(&dma_list_mutex); > + return dev_to_dma_chan(dev); > +} > +EXPORT_SYMBOL_GPL(dma_chan_from_dev_lock); > + New dma API should start from dmaengine Any one outside dmaengine need access dma_list_mutex? I'd like use dma_list_mutex directly. > +/** > + * dma_chan_from_dev_unlock - release the lock taken by dma_chan_from_dev_lock() > + * @chan: unused; matches the value produced by dma_chan_from_dev_lock() > + */ > +void dma_chan_from_dev_unlock(struct dma_chan *chan) > +{ > + mutex_unlock(&dma_list_mutex); > +} > +EXPORT_SYMBOL_GPL(dma_chan_from_dev_unlock); > + > static ssize_t memcpy_count_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > @@ -1098,6 +1124,7 @@ static int __dma_async_device_channel_register(struct dma_device *device, > > chan->dev->device.class = &dma_devclass; > chan->dev->device.parent = device->dev; > + chan->dev->device.groups = device->chan_groups; > chan->dev->chan = chan; > chan->dev->dev_id = device->dev_id; > if (!name) > diff --git a/drivers/dma/dmaengine.h b/drivers/dma/dmaengine.h > index 53f16d3f0029..224126e64d54 100644 > --- a/drivers/dma/dmaengine.h > +++ b/drivers/dma/dmaengine.h > @@ -182,6 +182,25 @@ dmaengine_desc_callback_valid(struct dmaengine_desc_callback *cb) > struct dma_chan *dma_get_slave_channel(struct dma_chan *chan); > struct dma_chan *dma_get_any_slave_channel(struct dma_device *device); > > +/* > + * dma_chan_from_dev_lock() / dma_chan_from_dev_unlock() bracket a critical > + * section across which a channel's struct device can be safely converted > + * back to its struct dma_chan: dma_chan_from_dev_lock() returns NULL if the > + * channel has already been unregistered, and the lock it takes must be held > + * for as long as the returned channel (or anything derived from it) is > + * accessed. > + * > + * Use these through the dma_chan_from_dev CLASS below rather than calling > + * them directly. > + */ > +struct dma_chan *dma_chan_from_dev_lock(struct device *dev); > +void dma_chan_from_dev_unlock(struct dma_chan *chan); > + > +DEFINE_CLASS(dma_chan_from_dev, struct dma_chan *, > + dma_chan_from_dev_unlock(_T), > + dma_chan_from_dev_lock(dev), > + struct device *dev) > + > #ifdef CONFIG_DEBUG_FS > #include > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h > index b3d251c9734e..f4e7861b2507 100644 > --- a/include/linux/dmaengine.h > +++ b/include/linux/dmaengine.h > @@ -803,6 +803,9 @@ struct dma_filter { > * @dev: struct device reference for dma mapping api > * @owner: owner module (automatically set based on the provided dev) > * @chan_ida: unique channel ID > + * @chan_groups: optional NULL-terminated array of sysfs attribute groups > + * added to each channel's struct device, for driver-specific per-channel > + * attributes > * @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. > @@ -886,6 +889,7 @@ struct dma_device { > struct device *dev; > struct module *owner; > struct ida chan_ida; > + const struct attribute_group **chan_groups; It is per channel group, why not put into dma_chan struct. Frank > > u32 src_addr_widths; > u32 dst_addr_widths; > -- > 2.47.3 >