Re: [PATCH 1/2] drm/i915/gem: Correct the locking and pin pattern for dma-buf (v5)

On Mon, Jul 12, 2021 at 06:12:33PM -0500, Jason Ekstrand wrote:

From: Thomas Hellström thomas.hellstrom@linux.intel.com

If our exported dma-bufs are imported by another instance of our driver, that instance will typically have the imported dma-bufs locked during dma_buf_map_attachment(). But the exporter also locks the same reservation object in the map_dma_buf() callback, which leads to recursive locking.

So taking the lock inside _pin_pages_unlocked() is incorrect.

Additionally, the current pinning code path is contrary to the defined way that pinning should occur.

Remove the explicit pin/unpin from the map/umap functions and move them to the attach/detach allowing correct locking to occur, and to match the static dma-buf drm_prime pattern.

Add a live selftest to exercise both dynamic and non-dynamic exports.

v2:

• Extend the selftest with a fake dynamic importer.
• Provide real pin and unpin callbacks to not abuse the interface.

v3: (ruhl)

• Remove the dynamic export support and move the pinning into the attach/detach path.

v4: (ruhl)

• Put pages does not need to assert on the dma-resv

v5: (jason)

• Lock around dma_buf_unmap_attachment() when emulating a dynamic importer in the subtests.
• Use pin_pages_unlocked

Reported-by: Michael J. Ruhl michael.j.ruhl@intel.com Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com Signed-off-by: Michael J. Ruhl michael.j.ruhl@intel.com Signed-off-by: Jason Ekstrand jason@jlekstrand.net Reviewed-by: Jason Ekstrand jason@jlekstrand.net

---

drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 43 +++++-- .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 118 +++++++++++++++++- 2 files changed, 147 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c index 616c3a2f1baf0..9a655f69a0671 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c @@ -12,6 +12,8 @@ #include "i915_gem_object.h" #include "i915_scatterlist.h"

+I915_SELFTEST_DECLARE(static bool force_different_devices;)

static struct drm_i915_gem_object *dma_buf_to_obj(struct dma_buf *buf) { return to_intel_bo(buf->priv); @@ -25,15 +27,11 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme struct scatterlist *src, *dst; int ret, i;

• ret = i915_gem_object_pin_pages_unlocked(obj);
• if (ret)

• goto err;
  

• /* Copy sg so that we make an independent mapping */ st = kmalloc(sizeof(struct sg_table), GFP_KERNEL); if (st == NULL) { ret = -ENOMEM;

• goto err_unpin_pages;
  

• goto err;
  

  }

  ret = sg_alloc_table(st, obj->mm.pages->nents, GFP_KERNEL);

@@ -58,8 +56,6 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme sg_free_table(st); err_free: kfree(st); -err_unpin_pages:

• i915_gem_object_unpin_pages(obj);

err: return ERR_PTR(ret); } @@ -68,13 +64,9 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment, struct sg_table *sg, enum dma_data_direction dir) {

• struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);
• dma_unmap_sgtable(attachment->dev, sg, dir, DMA_ATTR_SKIP_CPU_SYNC); sg_free_table(sg); kfree(sg);
• i915_gem_object_unpin_pages(obj);

}

static int i915_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct dma_buf_map *map) @@ -168,7 +160,31 @@ static int i915_gem_end_cpu_access(struct dma_buf *dma_buf, enum dma_data_direct return err; }

+/**

• • i915_gem_dmabuf_attach - Do any extra attach work necessary
• • @dmabuf: imported dma-buf
• • @attach: new attach to do work on
• */

+static int i915_gem_dmabuf_attach(struct dma_buf *dmabuf,

• 		  struct dma_buf_attachment *attach)
  

+{

• struct drm_i915_gem_object *obj = dma_buf_to_obj(dmabuf);
• return i915_gem_object_pin_pages_unlocked(obj);

+}

+static void i915_gem_dmabuf_detach(struct dma_buf *dmabuf,

• 		   struct dma_buf_attachment *attach)
  

+{

• struct drm_i915_gem_object *obj = dma_buf_to_obj(dmabuf);
• i915_gem_object_unpin_pages(obj);

+}

static const struct dma_buf_ops i915_dmabuf_ops = {

• .attach = i915_gem_dmabuf_attach,
• .detach = i915_gem_dmabuf_detach, .map_dma_buf = i915_gem_map_dma_buf, .unmap_dma_buf = i915_gem_unmap_dma_buf, .release = drm_gem_dmabuf_release,

@@ -204,6 +220,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj) struct sg_table *pages; unsigned int sg_page_sizes;

• assert_object_held(obj);
• pages = dma_buf_map_attachment(obj->base.import_attach, DMA_BIDIRECTIONAL); if (IS_ERR(pages))

@@ -241,7 +259,8 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev, if (dma_buf->ops == &i915_dmabuf_ops) { obj = dma_buf_to_obj(dma_buf); /* is it from our device? */

• if (obj->base.dev == dev) {
  

• if (obj->base.dev == dev &&
  

•     !I915_SELFTEST_ONLY(force_different_devices)) {
  /*
   * Importing dmabuf exported from out own gem increases
   * refcount on gem itself instead of f_count of dmabuf.
  

diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c index dd74bc09ec88d..3dc0f8b3cdab0 100644 --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c @@ -35,7 +35,7 @@ static int igt_dmabuf_export(void *arg) static int igt_dmabuf_import_self(void *arg) { struct drm_i915_private *i915 = arg;

• struct drm_i915_gem_object *obj;

• struct drm_i915_gem_object *obj, *import_obj; struct drm_gem_object *import; struct dma_buf *dmabuf; int err;

@@ -65,14 +65,127 @@ static int igt_dmabuf_import_self(void *arg) err = -EINVAL; goto out_import; }

• import_obj = to_intel_bo(import);

• i915_gem_object_lock(import_obj, NULL);

• err = ____i915_gem_object_get_pages(import_obj);

• i915_gem_object_unlock(import_obj);

• if (err) {

• pr_err("Same object dma-buf get_pages failed!\n");
  

• goto out_import;
  

• }

  err = 0;

out_import:

• i915_gem_object_put(to_intel_bo(import));

• i915_gem_object_put(import_obj);

+out_dmabuf:

• dma_buf_put(dmabuf);

+out:

• i915_gem_object_put(obj);
• return err;

+}

+static void igt_dmabuf_move_notify(struct dma_buf_attachment *attach) +{

• GEM_WARN_ON(1);

+}

+static const struct dma_buf_attach_ops igt_dmabuf_attach_ops = {

• .move_notify = igt_dmabuf_move_notify,

+};

+static int igt_dmabuf_import_same_driver(void *arg) +{

• struct drm_i915_private *i915 = arg;
• struct drm_i915_gem_object *obj, *import_obj;
• struct drm_gem_object *import;
• struct dma_buf *dmabuf;
• struct dma_buf_attachment *import_attach;
• struct sg_table *st;
• long timeout;
• int err;
• force_different_devices = true;
• obj = i915_gem_object_create_shmem(i915, PAGE_SIZE);
• if (IS_ERR(obj))

• goto out_ret;
  

• dmabuf = i915_gem_prime_export(&obj->base, 0);
• if (IS_ERR(dmabuf)) {

• pr_err("i915_gem_prime_export failed with err=%d\n",
  

•        (int)PTR_ERR(dmabuf));
  

• err = PTR_ERR(dmabuf);
  

• goto out;
  

• }
• import = i915_gem_prime_import(&i915->drm, dmabuf);
• if (IS_ERR(import)) {

• pr_err("i915_gem_prime_import failed with err=%d\n",
  

•        (int)PTR_ERR(import));
  

• err = PTR_ERR(import);
  

• goto out_dmabuf;
  

• }
• if (import == &obj->base) {

• pr_err("i915_gem_prime_import reused gem object!\n");
  

• err = -EINVAL;
  

• goto out_import;
  

• }
• import_obj = to_intel_bo(import);
• i915_gem_object_lock(import_obj, NULL);
• err = ____i915_gem_object_get_pages(import_obj);
• if (err) {

• pr_err("Different objects dma-buf get_pages failed!\n");
  

• i915_gem_object_unlock(import_obj);
  

• goto out_import;
  

• }
• /*

• * If the exported object is not in system memory, something
  

• * weird is going on. TODO: When p2p is supported, this is no
  

• * longer considered weird.
  

• */
  

• if (obj->mm.region != i915->mm.regions[INTEL_REGION_SMEM]) {

• pr_err("Exported dma-buf is not in system memory\n");
  

• err = -EINVAL;
  

• }
• i915_gem_object_unlock(import_obj);
• /* Now try a fake dynamic importer */
• import_attach = dma_buf_dynamic_attach(dmabuf, obj->base.dev->dev,

Since we don't do a fake dynamic importer please use the non-dynamic version here. I think just needs you to delete the attach_ops.

• 			       &igt_dmabuf_attach_ops,
  

• 			       NULL);
  

• if (IS_ERR(import_attach))

• goto out_import;
  

• dma_resv_lock(dmabuf->resv, NULL);

Also non-dynamic doesn't need dma_resv_lock here (dma-buf.c does that for you if needed).

• st = dma_buf_map_attachment(import_attach, DMA_BIDIRECTIONAL);
• dma_resv_unlock(dmabuf->resv);
• if (IS_ERR(st))

• goto out_detach;
  

• timeout = dma_resv_wait_timeout(dmabuf->resv, false, true, 5 * HZ);

And also not this one here.

With that:

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

• if (!timeout) {

• pr_err("dmabuf wait for exclusive fence timed out.\n");
  

• timeout = -ETIME;
  

• }
• err = timeout > 0 ? 0 : timeout;
• dma_resv_lock(dmabuf->resv, NULL);
• dma_buf_unmap_attachment(import_attach, st, DMA_BIDIRECTIONAL);
• dma_resv_unlock(dmabuf->resv);

+out_detach:

• dma_buf_detach(dmabuf, import_attach);

+out_import:

• i915_gem_object_put(import_obj);

out_dmabuf: dma_buf_put(dmabuf); out: i915_gem_object_put(obj); +out_ret:

• force_different_devices = false; return err;

}

@@ -286,6 +399,7 @@ int i915_gem_dmabuf_live_selftests(struct drm_i915_private *i915) { static const struct i915_subtest tests[] = { SUBTEST(igt_dmabuf_export),

• SUBTEST(igt_dmabuf_import_same_driver),
  

  };

  return i915_subtests(tests, i915);

-- 2.31.1