[Intel-gfx] [PATCH v3 4/5] drm/i915/gem: Fix same-driver-another-instance dma-buf export
Thomas Hellström
thomas.hellstrom at linux.intel.com
Tue Jun 29 09:36:19 UTC 2021
On 6/29/21 10:43 AM, Daniel Vetter wrote:
> On Mon, Jun 28, 2021 at 07:45:31PM +0000, Ruhl, Michael J wrote:
>>> -----Original Message-----
>>> From: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>>> Sent: Monday, June 28, 2021 10:46 AM
>>> To: intel-gfx at lists.freedesktop.org; dri-devel at lists.freedesktop.org
>>> Cc: Auld, Matthew <matthew.auld at intel.com>;
>>> maarten.lankhorst at linux.intel.com; Thomas Hellström
>>> <thomas.hellstrom at linux.intel.com>; Ruhl; Ruhl, Michael J
>>> <michael.j.ruhl at intel.com>
>>> Subject: [PATCH v3 4/5] drm/i915/gem: Fix same-driver-another-instance
>>> dma-buf export
>>>
>>> If our exported dma-bufs are imported by another instance of our driver,
>>> that instance will typically have the imported dma-bufs locked during
>>> map_attachment(). But the exporter also locks the same reservation
>>> object in the map_dma_buf() callback, which leads to recursive locking.
>>>
>>> Add a live selftest to catch this case, and as a workaround until
>>> we fully support dynamic import and export, declare the exporter dynamic
>>> by providing NOP pin() and unpin() functions. This means our map_dma_buf()
>>> callback will *always* get called locked, and by pinning unconditionally
>>> in i915_gem_map_dma_buf() we make sure we don't need to use the
>>> move_notify() functionality which is not yet implemented.
>> An interesting abuse of the interface, but it seems reasonable (for now) to me.
> Hm I'm not sure this is the best interface abuse, since if we combine this
> with amdgpu it goes boom. Also I thought the dynamic stuff is optional (or
> is that only for the importer).
I'm not sure what would go wrong here when combined with amdgpu? I
figure an amdgpu importer being dynamic, would expect to get notified
using move_notify() on move, but that never happens since the exported
bo is pinned. If it matters for interface abuse then I could add real
implementations of pin() and unpin(). But choosing to not evict a mapped
dma-buf must remain at the exporter's discretion and is not an interface
abuse IMO.
Could you point me to a case that would not work with this code?
> What I discussed a bit with Maarten on irc is to essentially emulate the
> rules of what a dynamic exporter would end up with with a non-dynamic
> importer: pin/unpin the buffer at attach/detach time. We could fake this
> in our attach/detach callbacks.
Yes, but that would only reimplement what's already in the dma-buf core?
Since we're about to add a real and correct implementation of this, that
sounds like a waste of time IMHO.
>
> At least I don't think it's the locking changes that saves us here, but
> the caching of the sgt list in attach/detach.
Yes that saves us for the case of a non-locking non-dynamic importer,
but for same-driver-another-instance, it's indeed the locking changes.
> As long as we hand-roll that
> we should be fine. So hand-rolling that feels like the best option to make
> sure we're not making this worse, as long as we haven't fully validated
> the true dynamic importer _and_ exporter case.
/Thomas
>
> Cheers, Daniel
>
>> Reviewed-by: Michael J. Ruhl <michael.j.ruhl at intel.com>
>>
>> Mike
>>
>>> Reported-by: Ruhl, Michael J <michael.j.ruhl at intel.com>
>>> Cc: Ruhl, Michael J <michael.j.ruhl at intel.com>
>>> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>>> ---
>>> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 31 ++++++-
>>> .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 81
>>> ++++++++++++++++++-
>>> 2 files changed, 108 insertions(+), 4 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..1d1eeb167d28 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);
>>> @@ -25,7 +27,9 @@ 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);
>>> + assert_object_held(obj);
>>> +
>>> + ret = i915_gem_object_pin_pages(obj);
>>> if (ret)
>>> goto err;
>>>
>>> @@ -168,6 +172,26 @@ static int i915_gem_end_cpu_access(struct dma_buf
>>> *dma_buf, enum dma_data_direct
>>> return err;
>>> }
>>>
>>> +/*
>>> + * As a workaround until we fully support dynamic import and export,
>>> + * declare the exporter dynamic by providing NOP pin() and unpin()
>>> functions.
>>> + * This means our i915_gem_map_dma_buf() callback will *always* get
>>> called
>>> + * locked, and by pinning unconditionally in i915_gem_map_dma_buf() we
>>> make
>>> + * sure we don't need to use the move_notify() functionality which is
>>> + * not yet implemented. Typically for the same-driver-another-instance case,
>>> + * i915_gem_map_dma_buf() will be called at importer attach time and the
>>> + * mapped sg_list will be cached by the dma-buf core for the
>>> + * duration of the attachment.
>>> + */
>>> +static int i915_gem_dmabuf_pin(struct dma_buf_attachment *attach)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> +static void i915_gem_dmabuf_unpin(struct dma_buf_attachment *attach)
>>> +{
>>> +}
>>> +
>>> static const struct dma_buf_ops i915_dmabuf_ops = {
>>> .map_dma_buf = i915_gem_map_dma_buf,
>>> .unmap_dma_buf = i915_gem_unmap_dma_buf,
>>> @@ -177,6 +201,8 @@ static const struct dma_buf_ops i915_dmabuf_ops = {
>>> .vunmap = i915_gem_dmabuf_vunmap,
>>> .begin_cpu_access = i915_gem_begin_cpu_access,
>>> .end_cpu_access = i915_gem_end_cpu_access,
>>> + .pin = i915_gem_dmabuf_pin,
>>> + .unpin = i915_gem_dmabuf_unpin,
>>> };
>>>
>>> struct dma_buf *i915_gem_prime_export(struct drm_gem_object
>>> *gem_obj, int flags)
>>> @@ -241,7 +267,8 @@ 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 dd74bc09ec88..24735d6c12a2 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 +65,90 @@ 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 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;
>>> + 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);
>>> +
>>> +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 +362,7 @@ 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
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