On Tue, Jul 03, 2018 at 01:46:44PM +0200, Christian König wrote: > Am 25.06.2018 um 11:12 schrieb Daniel Vetter: > > On Mon, Jun 25, 2018 at 10:22:31AM +0200, Daniel Vetter wrote: > > > On Fri, Jun 22, 2018 at 04:11:01PM +0200, Christian König wrote: > > > > First step towards unpinned DMA buf operation. > > > > > > > > I've checked the DRM drivers to potential locking of the reservation > > > > object, but essentially we need to audit all implementations of the > > > > dma_buf _ops for this to work. > > > > > > > > v2: reordered > > > > > > > > Signed-off-by: Christian König <christian.koenig@xxxxxxx> > > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > Ok I did review drivers a bit, but apparently not well enough by far. i915 > > CI is unhappy: > > > > https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_9400/fi-whl-u/igt@gem_mmap_gtt@xxxxxxxxxxxxxxxxxxxxxxxxxx > > > > So yeah inserting that lock in there isn't the most trivial thing :-/ > > > > I kinda assume that other drivers will have similar issues, e.g. omapdrm's > > use of dev->struct_mutex also very much looks like it'll result in a new > > locking inversion. > > Ah, crap. Already feared that this wouldn't be easy, but yeah that it is as > bad as this is rather disappointing. > > Thanks for the info, going to keep thinking about how to solve those issues. Side note: We want to make sure that drivers don't get the reservation_obj locking hierarchy wrong in other places (using dev->struct_mutex is kinda a pre-existing mis-use that we can't wish away retroactively unfortunately). One really important thing is that shrinker vs resv_obj must work with trylocks in the shrinker, so that you can allocate memory while holding reservation objects. One neat trick to teach lockdep about this would be to have a dummy if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { ww_mutex_lock(dma_buf->resv_obj); fs_reclaim_acquire(GFP_KERNEL); fs_reclaim_release(GFP_KERNEL); ww_mutex_unlock(dma_buf->resv_obj); } in dma_buf_init(). We're using the fs_reclaim_acquire/release check very successfully to improve our igt test coverage for i915.ko in other areas. Totally unrelated to dev->struct_mutex, but thoughts? Well for dev->struct_mutex we could at least decide on one true way to nest resv_obj vs. dev->struct_mutex as maybe an interim step, but not sure how much that would help. -Daniel > > Christian. > > > -Daniel > > > > > > --- > > > > drivers/dma-buf/dma-buf.c | 9 ++++++--- > > > > include/linux/dma-buf.h | 4 ++++ > > > > 2 files changed, 10 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > > > > index dc94e76e2e2a..49f23b791eb8 100644 > > > > --- a/drivers/dma-buf/dma-buf.c > > > > +++ b/drivers/dma-buf/dma-buf.c > > > > @@ -665,7 +665,9 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, > > > > if (WARN_ON(!attach || !attach->dmabuf)) > > > > return ERR_PTR(-EINVAL); > > > > - sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction); > > > > + reservation_object_lock(attach->dmabuf->resv, NULL); > > > > + sg_table = dma_buf_map_attachment_locked(attach, direction); > > > > + reservation_object_unlock(attach->dmabuf->resv); > > > > if (!sg_table) > > > > sg_table = ERR_PTR(-ENOMEM); > > > > @@ -715,8 +717,9 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, > > > > if (WARN_ON(!attach || !attach->dmabuf || !sg_table)) > > > > return; > > > > - attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, > > > > - direction); > > > > + reservation_object_lock(attach->dmabuf->resv, NULL); > > > > + dma_buf_unmap_attachment_locked(attach, sg_table, direction); > > > > + reservation_object_unlock(attach->dmabuf->resv); > > > > } > > > > EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment); > > > > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h > > > > index a25e754ae2f7..024658d1f22e 100644 > > > > --- a/include/linux/dma-buf.h > > > > +++ b/include/linux/dma-buf.h > > > > @@ -118,6 +118,8 @@ struct dma_buf_ops { > > > > * any other kind of sharing that the exporter might wish to make > > > > * available to buffer-users. > > > > * > > > > + * This is called with the dmabuf->resv object locked. > > > > + * > > > > * Returns: > > > > * > > > > * A &sg_table scatter list of or the backing storage of the DMA buffer, > > > > @@ -138,6 +140,8 @@ struct dma_buf_ops { > > > > * It should also unpin the backing storage if this is the last mapping > > > > * of the DMA buffer, it the exporter supports backing storage > > > > * migration. > > > > + * > > > > + * This is called with the dmabuf->resv object locked. > > > > */ > > > > void (*unmap_dma_buf)(struct dma_buf_attachment *, > > > > struct sg_table *, > > > > -- > > > > 2.14.1 > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
