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Message-ID: <a44aca93adc60ce56a64c50797a029631900172e.camel@crapouillou.net>
Subject: Re: [PATCH v3 3/4] usb: gadget: functionfs: Add DMABUF import
 interface
From: Paul Cercueil <paul@crapouillou.net>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Sumit Semwal
 <sumit.semwal@linaro.org>, Christian =?ISO-8859-1?Q?K=F6nig?=
 <christian.koenig@amd.com>, Jonathan Corbet <corbet@lwn.net>, Michael
 Hennerich <Michael.Hennerich@analog.com>, linux-doc@vger.kernel.org, 
 linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, 
 dri-devel@lists.freedesktop.org, Andrzej Pietrasiewicz
 <andrzej.p@collabora.com>,  linaro-mm-sig@lists.linaro.org, Nuno
 =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>, Jonathan Cameron
 <jic23@kernel.org>,  linux-media@vger.kernel.org
Date: Mon, 08 Jan 2024 15:21:21 +0100
In-Reply-To: <ZZvtEXL8DLPPdtPs@phenom.ffwll.local>
References: <20240108120056.22165-1-paul@crapouillou.net>
	 <20240108120056.22165-4-paul@crapouillou.net>
	 <ZZvtEXL8DLPPdtPs@phenom.ffwll.local>
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Hi Daniel (Sima?),

Le lundi 08 janvier 2024 =C3=A0 13:39 +0100, Daniel Vetter a =C3=A9crit=C2=
=A0:
> On Mon, Jan 08, 2024 at 01:00:55PM +0100, Paul Cercueil wrote:
> > This patch introduces three new ioctls. They all should be called
> > on a
> > data endpoint (ie. not ep0). They are:
> >=20
> > - FUNCTIONFS_DMABUF_ATTACH, which takes the file descriptor of a
> > DMABUF
> > =C2=A0 object to attach to the endpoint.
> >=20
> > - FUNCTIONFS_DMABUF_DETACH, which takes the file descriptor of the
> > =C2=A0 DMABUF to detach from the endpoint. Note that closing the
> > endpoint's
> > =C2=A0 file descriptor will automatically detach all attached DMABUFs.
> >=20
> > - FUNCTIONFS_DMABUF_TRANSFER, which requests a data transfer from /
> > to
> > =C2=A0 the given DMABUF. Its argument is a structure that packs the
> > DMABUF's
> > =C2=A0 file descriptor, the size in bytes to transfer (which should
> > generally
> > =C2=A0 be set to the size of the DMABUF), and a 'flags' field which is
> > unused
> > =C2=A0 for now.
> > =C2=A0 Before this ioctl can be used, the related DMABUF must be
> > attached
> > =C2=A0 with FUNCTIONFS_DMABUF_ATTACH.
> >=20
> > These three ioctls enable the FunctionFS code to transfer data
> > between
> > the USB stack and a DMABUF object, which can be provided by a
> > driver
> > from a completely different subsystem, in a zero-copy fashion.
> >=20
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> >=20
> > ---
> > v2:
> > - Make ffs_dma_resv_lock() static
> > - Add MODULE_IMPORT_NS(DMA_BUF);
> > - The attach/detach functions are now performed without locking the
> > =C2=A0 eps_lock spinlock. The transfer function starts with the spinloc=
k
> > =C2=A0 unlocked, then locks it before allocating and queueing the USB
> > =C2=A0 transfer.
> >=20
> > v3:
> > - Inline to_ffs_dma_fence() which was called only once.
> > - Simplify ffs_dma_resv_lock()
> > - Add comment explaining why we unref twice in ffs_dmabuf_detach()
> > - Document uapi struct usb_ffs_dmabuf_transfer_req and IOCTLs
> > ---
> > =C2=A0drivers/usb/gadget/function/f_fs.c=C2=A0 | 417
> > ++++++++++++++++++++++++++++
> > =C2=A0include/uapi/linux/usb/functionfs.h |=C2=A0 41 +++
> > =C2=A02 files changed, 458 insertions(+)
> >=20
> > diff --git a/drivers/usb/gadget/function/f_fs.c
> > b/drivers/usb/gadget/function/f_fs.c
> > index ed2a6d5fcef7..9df1f5abb0d4 100644
> > --- a/drivers/usb/gadget/function/f_fs.c
> > +++ b/drivers/usb/gadget/function/f_fs.c
> > @@ -15,6 +15,9 @@
> > =C2=A0/* #define VERBOSE_DEBUG */
> > =C2=A0
> > =C2=A0#include <linux/blkdev.h>
> > +#include <linux/dma-buf.h>
> > +#include <linux/dma-fence.h>
> > +#include <linux/dma-resv.h>
> > =C2=A0#include <linux/pagemap.h>
> > =C2=A0#include <linux/export.h>
> > =C2=A0#include <linux/fs_parser.h>
> > @@ -43,6 +46,8 @@
> > =C2=A0
> > =C2=A0#define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest
> > dice roll ;) */
> > =C2=A0
> > +MODULE_IMPORT_NS(DMA_BUF);
> > +
> > =C2=A0/* Reference counter handling */
> > =C2=A0static void ffs_data_get(struct ffs_data *ffs);
> > =C2=A0static void ffs_data_put(struct ffs_data *ffs);
> > @@ -124,6 +129,21 @@ struct ffs_ep {
> > =C2=A0	u8				num;
> > =C2=A0};
> > =C2=A0
> > +struct ffs_dmabuf_priv {
> > +	struct list_head entry;
> > +	struct kref ref;
> > +	struct dma_buf_attachment *attach;
> > +	spinlock_t lock;
> > +	u64 context;
> > +};
> > +
> > +struct ffs_dma_fence {
> > +	struct dma_fence base;
> > +	struct ffs_dmabuf_priv *priv;
> > +	struct sg_table *sgt;
> > +	enum dma_data_direction dir;
> > +};
> > +
> > =C2=A0struct ffs_epfile {
> > =C2=A0	/* Protects ep->ep and ep->req. */
> > =C2=A0	struct mutex			mutex;
> > @@ -197,6 +217,8 @@ struct ffs_epfile {
> > =C2=A0	unsigned char			isoc;	/* P: ffs-
> > >eps_lock */
> > =C2=A0
> > =C2=A0	unsigned char			_pad;
> > +
> > +	struct list_head		dmabufs;
> > =C2=A0};
> > =C2=A0
> > =C2=A0struct ffs_buffer {
> > @@ -1271,10 +1293,44 @@ static ssize_t ffs_epfile_read_iter(struct
> > kiocb *kiocb, struct iov_iter *to)
> > =C2=A0	return res;
> > =C2=A0}
> > =C2=A0
> > +static void ffs_dmabuf_release(struct kref *ref)
> > +{
> > +	struct ffs_dmabuf_priv *priv =3D container_of(ref, struct
> > ffs_dmabuf_priv, ref);
> > +	struct dma_buf_attachment *attach =3D priv->attach;
> > +	struct dma_buf *dmabuf =3D attach->dmabuf;
> > +
> > +	pr_debug("FFS DMABUF release\n");
> > +	dma_buf_detach(attach->dmabuf, attach);
> > +	dma_buf_put(dmabuf);
> > +
> > +	list_del(&priv->entry);
>=20
> I didn't find any locking for this list here.

Yeah. I'll add some.

> > +	kfree(priv);
> > +}
> > +
> > +static void ffs_dmabuf_get(struct dma_buf_attachment *attach)
> > +{
> > +	struct ffs_dmabuf_priv *priv =3D attach->importer_priv;
> > +
> > +	kref_get(&priv->ref);
> > +}
> > +
> > +static void ffs_dmabuf_put(struct dma_buf_attachment *attach)
> > +{
> > +	struct ffs_dmabuf_priv *priv =3D attach->importer_priv;
> > +
> > +	kref_put(&priv->ref, ffs_dmabuf_release);
> > +}
> > +
> > =C2=A0static int
> > =C2=A0ffs_epfile_release(struct inode *inode, struct file *file)
> > =C2=A0{
> > =C2=A0	struct ffs_epfile *epfile =3D inode->i_private;
> > +	struct ffs_dmabuf_priv *priv, *tmp;
> > +
> > +	/* Close all attached DMABUFs */
> > +	list_for_each_entry_safe(priv, tmp, &epfile->dmabufs,
> > entry) {
> > +		ffs_dmabuf_put(priv->attach);
> > +	}
> > =C2=A0
> > =C2=A0	__ffs_epfile_read_buffer_free(epfile);
> > =C2=A0	ffs_data_closed(epfile->ffs);
> > @@ -1282,6 +1338,328 @@ ffs_epfile_release(struct inode *inode,
> > struct file *file)
> > =C2=A0	return 0;
> > =C2=A0}
> > =C2=A0
> > +static void ffs_dmabuf_signal_done(struct ffs_dma_fence
> > *dma_fence, int ret)
> > +{
> > +	struct ffs_dmabuf_priv *priv =3D dma_fence->priv;
> > +	struct dma_fence *fence =3D &dma_fence->base;
> > +
> > +	dma_fence_get(fence);
> > +	fence->error =3D ret;
> > +	dma_fence_signal(fence);
> > +
> > +	dma_buf_unmap_attachment(priv->attach, dma_fence->sgt,
> > dma_fence->dir);
> > +	dma_fence_put(fence);
> > +	ffs_dmabuf_put(priv->attach);
>=20
> So this can in theory take the dma_resv lock, and if the usb
> completion
> isn't an unlimited worker this could hold up completion of future
> dma_fence, resulting in a deadlock.
>=20
> Needs to be checked how usb works, and if stalling indefinitely in
> the
> io_complete callback can hold up the usb stack you need to:
>=20
> - drop a dma_fence_begin/end_signalling annotations in here
> - pull out the unref stuff into a separate preallocated worker (or at
> =C2=A0 least the final unrefs for ffs_dma_buf).

Only ffs_dmabuf_put() can attempt to take the dma_resv and would have
to be in a worker, right? Everything else would be inside the
dma_fence_begin/end_signalling() annotations?

>=20
> > +}
> > +
> > +static void ffs_epfile_dmabuf_io_complete(struct usb_ep *ep,
> > +					=C2=A0 struct usb_request *req)
> > +{
> > +	pr_debug("FFS: DMABUF transfer complete, status=3D%d\n",
> > req->status);
> > +	ffs_dmabuf_signal_done(req->context, req->status);
> > +	usb_ep_free_request(ep, req);
> > +}
> > +
> > +static const char *ffs_dmabuf_get_driver_name(struct dma_fence
> > *fence)
> > +{
> > +	return "functionfs";
> > +}
> > +
> > +static const char *ffs_dmabuf_get_timeline_name(struct dma_fence
> > *fence)
> > +{
> > +	return "";
> > +}
> > +
> > +static void ffs_dmabuf_fence_release(struct dma_fence *fence)
> > +{
> > +	struct ffs_dma_fence *dma_fence =3D
> > +		container_of(fence, struct ffs_dma_fence, base);
> > +
> > +	kfree(dma_fence);
> > +}
> > +
> > +static const struct dma_fence_ops ffs_dmabuf_fence_ops =3D {
> > +	.get_driver_name	=3D ffs_dmabuf_get_driver_name,
> > +	.get_timeline_name	=3D ffs_dmabuf_get_timeline_name,
> > +	.release		=3D ffs_dmabuf_fence_release,
> > +};
> > +
> > +static int ffs_dma_resv_lock(struct dma_buf *dmabuf, bool
> > nonblock)
> > +{
> > +	int ret;
> > +
> > +	ret =3D dma_resv_lock_interruptible(dmabuf->resv, NULL);
> > +	if (ret) {
> > +		if (ret !=3D -EDEADLK)
> > +			return ret;
> > +		if (nonblock)
> > +			return -EBUSY;
> > +
> > +		ret =3D dma_resv_lock_slow_interruptible(dmabuf-
> > >resv, NULL);
>=20
> This is overkill, without a reservation context you will never get
> -EDEADLK and so never have to do slowpath locking. So just dead code.
>=20
> If you want to check, build with CONFIG_DEBUG_WW_MUTEX_SLOWPATH=3Dy

Ok.

>=20
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +static struct dma_buf_attachment *
> > +ffs_dmabuf_find_attachment(struct device *dev, struct dma_buf
> > *dmabuf,
> > +			=C2=A0=C2=A0 bool nonblock)
> > +{
> > +	struct dma_buf_attachment *elm, *attach =3D NULL;
> > +	int ret;
> > +
> > +	ret =3D ffs_dma_resv_lock(dmabuf, nonblock);
> > +	if (ret)
> > +		return ERR_PTR(ret);
> > +
> > +	list_for_each_entry(elm, &dmabuf->attachments, node) {
> > +		if (elm->dev =3D=3D dev) {
> > +			attach =3D elm;
> > +			break;
> > +		}
> > +	}
> > +
> > +	if (attach)
> > +		ffs_dmabuf_get(elm);
>=20
> This needs a kref_get_unless_zero or you can race with the final
> free.
>=20
> I'm not super keen that usb-gadget is noodling around in the
> attachment
> list like this, your own lookup structure (you have the dma-buf list
> already anyway to keep track of all attachments) would be much nicer.
> But
> the get_unless_zero I think is mandatory here for this weak
> reference.

Christian suggested to move that to a dma_buf function.
Alternatively I can browse my epfile->dmabufs list, sure - that won't
be hard to do. That's probably a better idea too.

>=20
> > +
> > +	dma_resv_unlock(dmabuf->resv);
> > +
> > +	return attach ?: ERR_PTR(-EPERM);
> > +}
> > +
> > +static int ffs_dmabuf_attach(struct file *file, int fd)
> > +{
> > +	struct ffs_epfile *epfile =3D file->private_data;
> > +	struct usb_gadget *gadget =3D epfile->ffs->gadget;
> > +	struct dma_buf_attachment *attach;
> > +	struct ffs_dmabuf_priv *priv;
> > +	struct dma_buf *dmabuf;
> > +	int err;
> > +
> > +	if (!gadget || !gadget->sg_supported)
> > +		return -EPERM;
> > +
> > +	dmabuf =3D dma_buf_get(fd);
> > +	if (IS_ERR(dmabuf))
> > +		return PTR_ERR(dmabuf);
> > +
> > +	attach =3D dma_buf_attach(dmabuf, gadget->dev.parent);
> > +	if (IS_ERR(attach)) {
> > +		err =3D PTR_ERR(attach);
> > +		goto err_dmabuf_put;
> > +	}
> > +
> > +	priv =3D kzalloc(sizeof(*priv), GFP_KERNEL);
> > +	if (!priv) {
> > +		err =3D -ENOMEM;
> > +		goto err_dmabuf_detach;
> > +	}
> > +
> > +	attach->importer_priv =3D priv;
> > +
> > +	priv->attach =3D attach;
> > +	spin_lock_init(&priv->lock);
> > +	kref_init(&priv->ref);
> > +	priv->context =3D dma_fence_context_alloc(1);
>=20
> Just to check: usb gagdet gurantees that all requests on an ep are
> ordered?

The documentation of usb_ep_queue() states that the transfer requests
are processed in FIFO order, yes.

>=20
> > +
> > +	list_add(&priv->entry, &epfile->dmabufs);
> > +
> > +	return 0;
> > +
> > +err_dmabuf_detach:
> > +	dma_buf_detach(dmabuf, attach);
> > +err_dmabuf_put:
> > +	dma_buf_put(dmabuf);
> > +
> > +	return err;
> > +}
> > +
> > +static int ffs_dmabuf_detach(struct file *file, int fd)
> > +{
> > +	struct ffs_epfile *epfile =3D file->private_data;
> > +	struct usb_gadget *gadget =3D epfile->ffs->gadget;
> > +	bool nonblock =3D file->f_flags & O_NONBLOCK;
> > +	struct dma_buf_attachment *attach;
> > +	struct dma_buf *dmabuf;
> > +	int ret =3D 0;
> > +
> > +	dmabuf =3D dma_buf_get(fd);
> > +	if (IS_ERR(dmabuf))
> > +		return PTR_ERR(dmabuf);
> > +
> > +	attach =3D ffs_dmabuf_find_attachment(gadget->dev.parent,
> > +					=C2=A0=C2=A0=C2=A0 dmabuf, nonblock);
> > +	if (IS_ERR(attach)) {
> > +		ret =3D PTR_ERR(attach);
> > +		goto out_dmabuf_put;
> > +	}
> > +
> > +	/*
> > +	 * Unref twice to release the reference obtained with
> > +	 * ffs_dmabuf_find_attachment() above, and the one
> > obtained in
> > +	 * ffs_dmabuf_attach().
> > +	 */
> > +	ffs_dmabuf_put(attach);
>=20
> This looks strange, what's stopping userspace from calling detach
> multiple
> times while a transfer is pending (so that the destruction is
> delayed)?
> That smells like a refcount underflow.

My idea was that the second ffs_dmabuf_put() would trigger
ffs_dmabuf_release(), which calls the list_del(); so a second call to
ffs_dmabuf_detach() would fail to find the attachment.

Indeed, if there's an on-going transfer, the refcount is higher, and
this breaks miserably.

Christian pointed out that it breaks if ffs_dmabuf_detach() is called
concurrently, but this is even worse :)


> You probably need to tie the refcounts you acquire in
> ffs_dmabuf_attach to
> epfile->dmabufs 1:1 to make sure there's no way userspace can pull
> you
> over the table. This is also the reason why I looked for the locking
> of
> that list, and didn't find it.

I'll change the code to atomically get the dma_buf_attachment and
remove it from the list.

>=20
> > +	ffs_dmabuf_put(attach);
> > +
> > +out_dmabuf_put:
> > +	dma_buf_put(dmabuf);
> > +	return ret;
> > +}
> > +
> > +static int ffs_dmabuf_transfer(struct file *file,
> > +			=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const struct
> > usb_ffs_dmabuf_transfer_req *req)
> > +{
> > +	bool dma_to_ram, nonblock =3D file->f_flags & O_NONBLOCK;
> > +	struct ffs_epfile *epfile =3D file->private_data;
> > +	struct usb_gadget *gadget =3D epfile->ffs->gadget;
> > +	struct dma_buf_attachment *attach;
> > +	struct ffs_dmabuf_priv *priv;
> > +	enum dma_data_direction dir;
> > +	struct ffs_dma_fence *fence;
> > +	struct usb_request *usb_req;
> > +	struct sg_table *sg_table;
> > +	struct dma_buf *dmabuf;
> > +	struct ffs_ep *ep;
> > +	int ret;
> > +
> > +	if (req->flags & ~USB_FFS_DMABUF_TRANSFER_MASK)
> > +		return -EINVAL;
> > +
> > +	dmabuf =3D dma_buf_get(req->fd);
> > +	if (IS_ERR(dmabuf))
> > +		return PTR_ERR(dmabuf);
> > +
> > +	if (req->length > dmabuf->size || req->length =3D=3D 0) {
> > +		ret =3D -EINVAL;
> > +		goto err_dmabuf_put;
> > +	}
> > +
> > +	attach =3D ffs_dmabuf_find_attachment(gadget->dev.parent,
> > +					=C2=A0=C2=A0=C2=A0 dmabuf, nonblock);
> > +	if (IS_ERR(attach)) {
> > +		ret =3D PTR_ERR(attach);
> > +		goto err_dmabuf_put;
> > +	}
> > +
> > +	priv =3D attach->importer_priv;
> > +
> > +	if (epfile->in)
> > +		dir =3D DMA_FROM_DEVICE;
> > +	else
> > +		dir =3D DMA_TO_DEVICE;
> > +
> > +	sg_table =3D dma_buf_map_attachment(attach, dir);
> > +	if (IS_ERR(sg_table)) {
> > +		ret =3D PTR_ERR(sg_table);
> > +		goto err_attachment_put;
> > +	}
> > +
> > +	ep =3D ffs_epfile_wait_ep(file);
> > +	if (IS_ERR(ep)) {
> > +		ret =3D PTR_ERR(ep);
> > +		goto err_unmap_attachment;
> > +	}
> > +
> > +	ret =3D ffs_dma_resv_lock(dmabuf, nonblock);
> > +	if (ret)
> > +		goto err_unmap_attachment;
> > +
> > +	/* Make sure we don't have writers */
> > +	if (!dma_resv_test_signaled(dmabuf->resv,
> > DMA_RESV_USAGE_WRITE)) {
> > +		pr_debug("FFS WRITE fence is not signaled\n");
> > +		ret =3D -EBUSY;
> > +		goto err_resv_unlock;
> > +	}
> > +
> > +	dma_to_ram =3D dir =3D=3D DMA_FROM_DEVICE;
> > +
> > +	/* If we're writing to the DMABUF, make sure we don't have
> > readers */
> > +	if (dma_to_ram &&
> > +	=C2=A0=C2=A0=C2=A0 !dma_resv_test_signaled(dmabuf->resv,
> > DMA_RESV_USAGE_READ)) {
> > +		pr_debug("FFS READ fence is not signaled\n");
> > +		ret =3D -EBUSY;
> > +		goto err_resv_unlock;
> > +	}
> > +
> > +	ret =3D dma_resv_reserve_fences(dmabuf->resv, 1);
> > +	if (ret)
> > +		goto err_resv_unlock;
> > +
> > +	fence =3D kmalloc(sizeof(*fence), GFP_KERNEL);
> > +	if (!fence) {
> > +		ret =3D -ENOMEM;
> > +		goto err_resv_unlock;
> > +	}
> > +
> > +	fence->sgt =3D sg_table;
> > +	fence->dir =3D dir;
> > +	fence->priv =3D priv;
> > +
> > +	dma_fence_init(&fence->base, &ffs_dmabuf_fence_ops,
> > +		=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &priv->lock, priv->context, 0);
>=20
> You need a real seqno here or things break with fence merging. Or
> alternatively unordered dma_fence (which are implemented by
> allocating a
> new context for each fence, maybe we should change that eventually
> ...).

Understood.

> > +
> > +	spin_lock_irq(&epfile->ffs->eps_lock);
> > +
> > +	/* In the meantime, endpoint got disabled or changed. */
> > +	if (epfile->ep !=3D ep) {
> > +		ret =3D -ESHUTDOWN;
> > +		goto err_fence_put;
> > +	}
> > +
> > +	usb_req =3D usb_ep_alloc_request(ep->ep, GFP_ATOMIC);
> > +	if (!usb_req) {
> > +		ret =3D -ENOMEM;
> > +		goto err_fence_put;
> > +	}
> > +
> > +	dma_resv_add_fence(dmabuf->resv, &fence->base,
> > +			=C2=A0=C2=A0 dma_resv_usage_rw(dma_to_ram));
> > +	dma_resv_unlock(dmabuf->resv);
> > +
> > +	/* Now that the dma_fence is in place, queue the transfer.
> > */
> > +
> > +	usb_req->length =3D req->length;
> > +	usb_req->buf =3D NULL;
> > +	usb_req->sg =3D sg_table->sgl;
> > +	usb_req->num_sgs =3D sg_nents_for_len(sg_table->sgl, req-
> > >length);
> > +	usb_req->sg_was_mapped =3D true;
> > +	usb_req->context=C2=A0 =3D fence;
> > +	usb_req->complete =3D ffs_epfile_dmabuf_io_complete;
> > +
> > +	ret =3D usb_ep_queue(ep->ep, usb_req, GFP_ATOMIC);
> > +	if (ret) {
> > +		usb_ep_free_request(ep->ep, usb_req);
> > +
> > +		spin_unlock_irq(&epfile->ffs->eps_lock);
> > +
> > +		pr_warn("FFS: Failed to queue DMABUF: %d\n", ret);
> > +		ffs_dmabuf_signal_done(fence, ret);
> > +		goto out_dma_buf_put;
> > +	}
> > +
> > +	spin_unlock_irq(&epfile->ffs->eps_lock);
> > +
> > +out_dma_buf_put:
> > +	dma_buf_put(dmabuf);
> > +
> > +	return ret;
> > +
> > +err_fence_put:
> > +	spin_unlock_irq(&epfile->ffs->eps_lock);
> > +	dma_fence_put(&fence->base);
> > +err_resv_unlock:
> > +	dma_resv_unlock(dmabuf->resv);
> > +err_unmap_attachment:
> > +	dma_buf_unmap_attachment(attach, sg_table, dir);
> > +err_attachment_put:
> > +	ffs_dmabuf_put(attach);
> > +err_dmabuf_put:
> > +	dma_buf_put(dmabuf);
> > +
> > +	return ret;
> > +}
> > +
> > =C2=A0static long ffs_epfile_ioctl(struct file *file, unsigned code,
> > =C2=A0			=C2=A0=C2=A0=C2=A0=C2=A0 unsigned long value)
> > =C2=A0{
> > @@ -1292,6 +1670,44 @@ static long ffs_epfile_ioctl(struct file
> > *file, unsigned code,
> > =C2=A0	if (WARN_ON(epfile->ffs->state !=3D FFS_ACTIVE))
> > =C2=A0		return -ENODEV;
> > =C2=A0
> > +	switch (code) {
> > +	case FUNCTIONFS_DMABUF_ATTACH:
> > +	{
> > +		int fd;
> > +
> > +		if (copy_from_user(&fd, (void __user *)value,
> > sizeof(fd))) {
> > +			ret =3D -EFAULT;
> > +			break;
> > +		}
> > +
> > +		return ffs_dmabuf_attach(file, fd);
> > +	}
> > +	case FUNCTIONFS_DMABUF_DETACH:
> > +	{
> > +		int fd;
> > +
> > +		if (copy_from_user(&fd, (void __user *)value,
> > sizeof(fd))) {
> > +			ret =3D -EFAULT;
> > +			break;
> > +		}
> > +
> > +		return ffs_dmabuf_detach(file, fd);
> > +	}
> > +	case FUNCTIONFS_DMABUF_TRANSFER:
> > +	{
> > +		struct usb_ffs_dmabuf_transfer_req req;
> > +
> > +		if (copy_from_user(&req, (void __user *)value,
> > sizeof(req))) {
> > +			ret =3D -EFAULT;
> > +			break;
> > +		}
> > +
> > +		return ffs_dmabuf_transfer(file, &req);
> > +	}
> > +	default:
> > +		break;
> > +	}
> > +
> > =C2=A0	/* Wait for endpoint to be enabled */
> > =C2=A0	ep =3D ffs_epfile_wait_ep(file);
> > =C2=A0	if (IS_ERR(ep))
> > @@ -1869,6 +2285,7 @@ static int ffs_epfiles_create(struct ffs_data
> > *ffs)
> > =C2=A0	for (i =3D 1; i <=3D count; ++i, ++epfile) {
> > =C2=A0		epfile->ffs =3D ffs;
> > =C2=A0		mutex_init(&epfile->mutex);
> > +		INIT_LIST_HEAD(&epfile->dmabufs);
> > =C2=A0		if (ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
> > =C2=A0			sprintf(epfile->name, "ep%02x", ffs-
> > >eps_addrmap[i]);
> > =C2=A0		else
> > diff --git a/include/uapi/linux/usb/functionfs.h
> > b/include/uapi/linux/usb/functionfs.h
> > index 078098e73fd3..9f88de9c3d66 100644
> > --- a/include/uapi/linux/usb/functionfs.h
> > +++ b/include/uapi/linux/usb/functionfs.h
> > @@ -86,6 +86,22 @@ struct usb_ext_prop_desc {
> > =C2=A0	__le16	wPropertyNameLength;
> > =C2=A0} __attribute__((packed));
> > =C2=A0
> > +/* Flags for usb_ffs_dmabuf_transfer_req->flags (none for now) */
> > +#define USB_FFS_DMABUF_TRANSFER_MASK	0x0
> > +
> > +/**
> > + * struct usb_ffs_dmabuf_transfer_req - Transfer request for a
> > DMABUF object
> > + * @fd:		file descriptor of the DMABUF object
> > + * @flags:	one or more USB_FFS_DMABUF_TRANSFER_* flags
> > + * @length:	number of bytes used in this DMABUF for the data
> > transfer.
> > + *		Should generally be set to the DMABUF's size.
> > + */
> > +struct usb_ffs_dmabuf_transfer_req {
> > +	int fd;
> > +	__u32 flags;
> > +	__u64 length;
> > +} __attribute__((packed));
> > +
> > =C2=A0#ifndef __KERNEL__
> > =C2=A0
> > =C2=A0/*
> > @@ -290,6 +306,31 @@ struct usb_functionfs_event {
> > =C2=A0#define	FUNCTIONFS_ENDPOINT_DESC	_IOR('g', 130, \
> > =C2=A0					=C2=A0=C2=A0=C2=A0=C2=A0 struct
> > usb_endpoint_descriptor)
> > =C2=A0
> > +/*
> > + * Attach the DMABUF object, identified by its file descriptor, to
> > the
> > + * data endpoint. Returns zero on success, and a negative errno
> > value
> > + * on error.
> > + */
> > +#define FUNCTIONFS_DMABUF_ATTACH	_IOW('g', 131, int)
> > +
> > =C2=A0
> > +/*
> > + * Detach the given DMABUF object, identified by its file
> > descriptor,
> > + * from the data endpoint. Returns zero on success, and a negative
> > + * errno value on error. Note that closing the endpoint's file
> > + * descriptor will automatically detach all attached DMABUFs.
> > + */
> > +#define FUNCTIONFS_DMABUF_DETACH	_IOW('g', 132, int)
> > +
> > +/*
> > + * Enqueue the previously attached DMABUF to the transfer queue.
> > + * The argument is a structure that packs the DMABUF's file
> > descriptor,
> > + * the size in bytes to transfer (which should generally
> > correspond to
> > + * the size of the DMABUF), and a 'flags' field which is unused
> > + * for now. Returns zero on success, and a negative errno value on
> > + * error.
> > + */
> > +#define FUNCTIONFS_DMABUF_TRANSFER	_IOW('g', 133, \
> > +					=C2=A0=C2=A0=C2=A0=C2=A0 struct
> > usb_ffs_dmabuf_transfer_req)
> > =C2=A0
> > =C2=A0#endif /* _UAPI__LINUX_FUNCTIONFS_H__ */
>=20
> Only things I've found are (I think at least) bugs in the usb gadget
> logic, not directly in how dma-buf/fence is used. The only thing I've
> noticed is the lack of actual dma_fence seqno (which I think
> Christian
> already pointed out in an already review, looking at archives at
> least).
> With that addressed:
>=20
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>=20
> Cheers, Sima

Thanks for the review!

Cheers,
-Paul