Re: [PATCH v3] dma-buf: remove restriction of IOCTL:DMA_BUF_SET_NAME

[Christian König]

Am 26.10.21 um 13:52 schrieb guangming.cao@xxxxxxxxxxxx:
> From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
>
> On Tue, 2021-10-26 at 13:18 +0200, Christian König wrote:
> > Am 14.10.21 um 12:25 schrieb guangming.cao@xxxxxxxxxxxx:
> > > From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
> > >
> > > In this patch(https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.freedesktop.org%2Fpatch%2F310349&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C6652f423b96547b8321308d998772121%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637708459727236977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=4EFg60sCxQzNuMKB0VjhbpvoeGlcAbofErMtcjPtIfw%3D&amp;reserved=0),
> > > it add a new IOCTL to support dma-buf user to set debug name.
> > >
> > > But it also added a limitation of this IOCTL, it needs the
> > > attachments of dmabuf should be empty, otherwise it will fail.
> > >
> > > For the original series, the idea was that allowing name change
> > > mid-use could confuse the users about the dma-buf.
> > > However, the rest of the series also makes sure each dma-buf have a
> > > unique
> > > inode(https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.freedesktop.org%2Fpatch%2F310387%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C6652f423b96547b8321308d998772121%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637708459727236977%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=c%2Bbso%2BSxiPjwlv%2B9tAzA4x0gf5UktREhSiAsODFkihk%3D&amp;reserved=0), and any
> > > accounting
> > > should probably use that, without relying on the name as much.
> > >
> > > So, removing this restriction will let dma-buf userspace users to
> > > use it
> > > more comfortably and without any side effect.
> > >
> > > Signed-off-by: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
> > We could now cleanup the return value from dma_buf_set_name() into a
> > void since that function can't fail any more as far as I can see.
> >
> > But that isn't mandatory I think, patch is Reviewed-by: Christian
> > König
> > <christian.koenig@xxxxxxx>
> So, here is no need to check return value of 'strndup_user',
> just return without error code if the almost impossible error occurs?

Good point, totally missed that one.

In that case I'm going to push the patch to drm-misc-next as is.

Regards,
Christian.

> Guangming.
>
> > Regards,
> > Christian.
> >
> > > ---
> > >    drivers/dma-buf/dma-buf.c | 17 +++--------------
> > >    1 file changed, 3 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > > index 511fe0d217a0..5fbb3a2068a3 100644
> > > --- a/drivers/dma-buf/dma-buf.c
> > > +++ b/drivers/dma-buf/dma-buf.c
> > > @@ -325,10 +325,8 @@ static __poll_t dma_buf_poll(struct file
> > > *file, poll_table *poll)
> > >    
> > >    /**
> > >     * dma_buf_set_name - Set a name to a specific dma_buf to track
> > > the usage.
> > > - * The name of the dma-buf buffer can only be set when the dma-buf
> > > is not
> > > - * attached to any devices. It could theoritically support
> > > changing the
> > > - * name of the dma-buf if the same piece of memory is used for
> > > multiple
> > > - * purpose between different devices.
> > > + * It could support changing the name of the dma-buf if the same
> > > + * piece of memory is used for multiple purpose between different
> > > devices.
> > >     *
> > >     * @dmabuf: [in]     dmabuf buffer that will be renamed.
> > >     * @buf:    [in]     A piece of userspace memory that contains
> > > the name of
> > > @@ -341,25 +339,16 @@ static __poll_t dma_buf_poll(struct file
> > > *file, poll_table *poll)
> > >    static long dma_buf_set_name(struct dma_buf *dmabuf, const char
> > > __user *buf)
> > >    {
> > >    	char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
> > > -	long ret = 0;
> > >    
> > >    	if (IS_ERR(name))
> > >    		return PTR_ERR(name);
> > >    
> > > -	dma_resv_lock(dmabuf->resv, NULL);
> > > -	if (!list_empty(&dmabuf->attachments)) {
> > > -		ret = -EBUSY;
> > > -		kfree(name);
> > > -		goto out_unlock;
> > > -	}
> > >    	spin_lock(&dmabuf->name_lock);
> > >    	kfree(dmabuf->name);
> > >    	dmabuf->name = name;
> > >    	spin_unlock(&dmabuf->name_lock);
> > >    
> > > -out_unlock:
> > > -	dma_resv_unlock(dmabuf->resv);
> > > -	return ret;
> > > +	return 0;
> > >    }
> > >    
> > >    static long dma_buf_ioctl(struct file *file,