[PATCH] dma-buf: Use dma_fence_unwrap_for_each when importing fences

[Jason Ekstrand]

On Sun, 2022-08-07 at 18:35 +0200, Christian König wrote:
> Am 02.08.22 um 23:01 schrieb Jason Ekstrand:
> > Ever since 68129f431faa ("dma-buf: warn about containers in
> > dma_resv object"),
> > dma_resv_add_shared_fence will warn if you attempt to add a
> > container fence.
> > While most drivers were fine, fences can also be added to a
> > dma_resv via the
> > recently added DMA_BUF_IOCTL_IMPORT_SYNC_FILE.  Use
> > dma_fence_unwrap_for_each
> > to add each fence one at a time.
> > 
> > Fixes: 594740497e99 ("dma-buf: Add an API for importing sync files
> > (v10)")
> > Signed-off-by: Jason Ekstrand <jason.ekstrand at collabora.com>
> > Reported-by: Sarah Walker <Sarah.Walker at imgtec.com>
> > Cc: Christian König <christian.koenig at amd.com>
> > ---
> >   drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++------
> >   1 file changed, 17 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 630133284e2b..8d5d45112f52 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -15,6 +15,7 @@
> >   #include <linux/slab.h>
> >   #include <linux/dma-buf.h>
> >   #include <linux/dma-fence.h>
> > +#include <linux/dma-fence-unwrap.h>
> >   #include <linux/anon_inodes.h>
> >   #include <linux/export.h>
> >   #include <linux/debugfs.h>
> > @@ -391,8 +392,10 @@ static long dma_buf_import_sync_file(struct
> > dma_buf *dmabuf,
> >                                      const void __user *user_data)
> >   {
> >         struct dma_buf_import_sync_file arg;
> > -       struct dma_fence *fence;
> > +       struct dma_fence *fence, *f;
> >         enum dma_resv_usage usage;
> > +       struct dma_fence_unwrap iter;
> > +       unsigned int num_fences;
> >         int ret = 0;
> >   
> >         if (copy_from_user(&arg, user_data, sizeof(arg)))
> > @@ -411,13 +414,21 @@ static long dma_buf_import_sync_file(struct
> > dma_buf *dmabuf,
> >         usage = (arg.flags & DMA_BUF_SYNC_WRITE) ?
> > DMA_RESV_USAGE_WRITE :
> >                                                   
> > DMA_RESV_USAGE_READ;
> >   
> > -       dma_resv_lock(dmabuf->resv, NULL);
> > +       num_fences = 0;
> > +       dma_fence_unwrap_for_each(f, &iter, fence)
> > +               ++num_fences;
> >   
> > -       ret = dma_resv_reserve_fences(dmabuf->resv, 1);
> > -       if (!ret)
> > -               dma_resv_add_fence(dmabuf->resv, fence, usage);
> > +       if (num_fences > 0) {
> > +               dma_resv_lock(dmabuf->resv, NULL);
> >   
> > -       dma_resv_unlock(dmabuf->resv);
> > +               ret = dma_resv_reserve_fences(dmabuf->resv,
> > num_fences);
> 
> That looks like it is misplaced.
> 
> You *must* only lock the reservation object once and then add all
> fences 
> in one go.

That's what I'm doing.  Lock, reserve, add a bunch, unlock.  I am
assuming that the iterator won't suddenly want to iterate more fences
between my initial count and when I go to add them but I think that
assumption is ok.

--Jason


> Thinking now about it we probably had a bug around that before as
> well. 
> Going to double check tomorrow.
> 
> Regards,
> Christian.
> 
> > +               if (!ret) {
> > +                       dma_fence_unwrap_for_each(f, &iter, fence)
> > +                               dma_resv_add_fence(dmabuf->resv, f,
> > usage);
> > +               }
> > +
> > +               dma_resv_unlock(dmabuf->resv);
> > +       }
> >   
> >         dma_fence_put(fence);
> >   
>