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@amd.com
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
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_mma...
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.-- 2.14.1
-- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch