[PATCH 1/2] drm/i915/gem: Correct the locking and pin pattern for dma-buf
Daniel Vetter
daniel at ffwll.ch
Fri Jul 2 17:09:39 UTC 2021
On Thu, Jul 1, 2021 at 4:24 PM Michael J. Ruhl <michael.j.ruhl at intel.com> wrote:
>
> From: Thomas Hellström <thomas.hellstrom at 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.
>
> Reported-by: Michael J. Ruhl <michael.j.ruhl at intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Signed-off-by: Michael J. Ruhl <michael.j.ruhl at intel.com>
CI splat is because I got the locking rules wrong, I thought
->attach/detach are called under the dma_resv_lock, because when we
used the old dma_buf->lock those calls where protected by that lock
under the same critical section as adding/removing from the list. But
we changed that in
f45f57cce584 ("dma-buf: stop using the dmabuf->lock so much v2")
15fd552d186c ("dma-buf: change DMA-buf locking convention v3")
Because keeping dma_resv_lock over ->attach/detach would go boom on
all the ttm drivers, which pin/unpin the buffer in there. Iow we need
the unlocked version there, but also having this split up is a bit
awkward and might be good to patch up so that it's atomic again. Would
mean updating a bunch of drivers. Christian, any thoughts?
Mike, for now I'd just keep using the _unlocked variants and we should be fine.
-Daniel
> ---
> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 46 ++++++--
> .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 111 +++++++++++++++++-
> 2 files changed, 143 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 616c3a2f1baf..00338c8d3739 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 +160,32 @@ 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);
> +
> + assert_object_held(obj);
> + return i915_gem_object_pin_pages(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 +221,8 @@ 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))
> @@ -219,6 +238,8 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj)
> static void i915_gem_object_put_pages_dmabuf(struct drm_i915_gem_object *obj,
> struct sg_table *pages)
> {
> + assert_object_held(obj);
> +
> dma_buf_unmap_attachment(obj->base.import_attach, pages,
> DMA_BIDIRECTIONAL);
> }
> @@ -241,7 +262,8 @@ 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_differnt_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 dd74bc09ec88..10a113cc00a5 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 +65,120 @@ 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 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,
> + &igt_dmabuf_attach_ops,
> + NULL);
> + if (IS_ERR(import_attach))
> + goto out_import;
> +
> + dma_resv_lock(dmabuf->resv, NULL);
> + 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);
> + if (!timeout) {
> + pr_err("dmabuf wait for exclusive fence timed out.\n");
> + timeout = -ETIME;
> + }
> + err = timeout > 0 ? 0 : timeout;
> + dma_buf_unmap_attachment(import_attach, st, DMA_BIDIRECTIONAL);
> +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 +392,7 @@ 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
More information about the dri-devel
mailing list