| Message ID | 20220831153757.97381-7-dmitry.osipenko@collabora.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Move all drivers to a common dma-buf locking convention | expand |
Am 31.08.22 um 17:37 schrieb Dmitry Osipenko: > Prepare i915 driver to the common dynamic dma-buf locking convention > by starting to use the unlocked versions of dma-buf API functions > and handling cases where importer now holds the reservation lock. > > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Acked-by: Christian König <christian.koenig@amd.com>, but it's probably best if somebody from the Intel guys take a look as well. > --- > drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 +- > drivers/gpu/drm/i915/gem/i915_gem_object.c | 12 ++++++++++++ > .../gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c | 16 ++++++++-------- > 3 files changed, 21 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c > index f5062d0c6333..07eee1c09aaf 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c > @@ -72,7 +72,7 @@ static int i915_gem_dmabuf_vmap(struct dma_buf *dma_buf, > struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf); > void *vaddr; > > - vaddr = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB); > + vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB); > if (IS_ERR(vaddr)) > return PTR_ERR(vaddr); > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c > index 389e9f157ca5..7e2a9b02526c 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c > @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915, > continue; > } > > + /* > + * dma_buf_unmap_attachment() requires reservation to be > + * locked. The imported GEM shouldn't share reservation lock, > + * so it's safe to take the lock. > + */ > + if (obj->base.import_attach) > + i915_gem_object_lock(obj, NULL); > + > __i915_gem_object_pages_fini(obj); > + > + if (obj->base.import_attach) > + i915_gem_object_unlock(obj); > + > __i915_gem_free_object(obj); > > /* But keep the pointer alive for RCU-protected lookups */ > 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 62c61af77a42..9e3ed634aa0e 100644 > --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c > +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c > @@ -213,7 +213,7 @@ static int igt_dmabuf_import_same_driver(struct drm_i915_private *i915, > goto out_import; > } > > - st = dma_buf_map_attachment(import_attach, DMA_BIDIRECTIONAL); > + st = dma_buf_map_attachment_unlocked(import_attach, DMA_BIDIRECTIONAL); > if (IS_ERR(st)) { > err = PTR_ERR(st); > goto out_detach; > @@ -226,7 +226,7 @@ static int igt_dmabuf_import_same_driver(struct drm_i915_private *i915, > timeout = -ETIME; > } > err = timeout > 0 ? 0 : timeout; > - dma_buf_unmap_attachment(import_attach, st, DMA_BIDIRECTIONAL); > + dma_buf_unmap_attachment_unlocked(import_attach, st, DMA_BIDIRECTIONAL); > out_detach: > dma_buf_detach(dmabuf, import_attach); > out_import: > @@ -296,7 +296,7 @@ static int igt_dmabuf_import(void *arg) > goto out_obj; > } > > - err = dma_buf_vmap(dmabuf, &map); > + err = dma_buf_vmap_unlocked(dmabuf, &map); > dma_map = err ? NULL : map.vaddr; > if (!dma_map) { > pr_err("dma_buf_vmap failed\n"); > @@ -337,7 +337,7 @@ static int igt_dmabuf_import(void *arg) > > err = 0; > out_dma_map: > - dma_buf_vunmap(dmabuf, &map); > + dma_buf_vunmap_unlocked(dmabuf, &map); > out_obj: > i915_gem_object_put(obj); > out_dmabuf: > @@ -358,7 +358,7 @@ static int igt_dmabuf_import_ownership(void *arg) > if (IS_ERR(dmabuf)) > return PTR_ERR(dmabuf); > > - err = dma_buf_vmap(dmabuf, &map); > + err = dma_buf_vmap_unlocked(dmabuf, &map); > ptr = err ? NULL : map.vaddr; > if (!ptr) { > pr_err("dma_buf_vmap failed\n"); > @@ -367,7 +367,7 @@ static int igt_dmabuf_import_ownership(void *arg) > } > > memset(ptr, 0xc5, PAGE_SIZE); > - dma_buf_vunmap(dmabuf, &map); > + dma_buf_vunmap_unlocked(dmabuf, &map); > > obj = to_intel_bo(i915_gem_prime_import(&i915->drm, dmabuf)); > if (IS_ERR(obj)) { > @@ -418,7 +418,7 @@ static int igt_dmabuf_export_vmap(void *arg) > } > i915_gem_object_put(obj); > > - err = dma_buf_vmap(dmabuf, &map); > + err = dma_buf_vmap_unlocked(dmabuf, &map); > ptr = err ? NULL : map.vaddr; > if (!ptr) { > pr_err("dma_buf_vmap failed\n"); > @@ -435,7 +435,7 @@ static int igt_dmabuf_export_vmap(void *arg) > memset(ptr, 0xc5, dmabuf->size); > > err = 0; > - dma_buf_vunmap(dmabuf, &map); > + dma_buf_vunmap_unlocked(dmabuf, &map); > out: > dma_buf_put(dmabuf); > return err;
On 9/1/22 09:45, Christian König wrote: > Am 31.08.22 um 17:37 schrieb Dmitry Osipenko: >> Prepare i915 driver to the common dynamic dma-buf locking convention >> by starting to use the unlocked versions of dma-buf API functions >> and handling cases where importer now holds the reservation lock. >> >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> > > Acked-by: Christian König <christian.koenig@amd.com>, but it's probably > best if somebody from the Intel guys take a look as well. + Chris Wilson, who touched locks of __i915_gem_free_objects() recently >> --- >> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 +- >> drivers/gpu/drm/i915/gem/i915_gem_object.c | 12 ++++++++++++ >> .../gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c | 16 ++++++++-------- >> 3 files changed, 21 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >> b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >> index f5062d0c6333..07eee1c09aaf 100644 >> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >> @@ -72,7 +72,7 @@ static int i915_gem_dmabuf_vmap(struct dma_buf >> *dma_buf, >> struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf); >> void *vaddr; >> - vaddr = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB); >> + vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB); >> if (IS_ERR(vaddr)) >> return PTR_ERR(vaddr); >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c >> b/drivers/gpu/drm/i915/gem/i915_gem_object.c >> index 389e9f157ca5..7e2a9b02526c 100644 >> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >> drm_i915_private *i915, >> continue; >> } >> + /* >> + * dma_buf_unmap_attachment() requires reservation to be >> + * locked. The imported GEM shouldn't share reservation lock, >> + * so it's safe to take the lock. >> + */ >> + if (obj->base.import_attach) >> + i915_gem_object_lock(obj, NULL); >> + >> __i915_gem_object_pages_fini(obj); >> + >> + if (obj->base.import_attach) >> + i915_gem_object_unlock(obj); >> + >> __i915_gem_free_object(obj); >> /* But keep the pointer alive for RCU-protected lookups */ >> 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 62c61af77a42..9e3ed634aa0e 100644 >> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c >> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c >> @@ -213,7 +213,7 @@ static int igt_dmabuf_import_same_driver(struct >> drm_i915_private *i915, >> goto out_import; >> } >> - st = dma_buf_map_attachment(import_attach, DMA_BIDIRECTIONAL); >> + st = dma_buf_map_attachment_unlocked(import_attach, >> DMA_BIDIRECTIONAL); >> if (IS_ERR(st)) { >> err = PTR_ERR(st); >> goto out_detach; >> @@ -226,7 +226,7 @@ static int igt_dmabuf_import_same_driver(struct >> drm_i915_private *i915, >> timeout = -ETIME; >> } >> err = timeout > 0 ? 0 : timeout; >> - dma_buf_unmap_attachment(import_attach, st, DMA_BIDIRECTIONAL); >> + dma_buf_unmap_attachment_unlocked(import_attach, st, >> DMA_BIDIRECTIONAL); >> out_detach: >> dma_buf_detach(dmabuf, import_attach); >> out_import: >> @@ -296,7 +296,7 @@ static int igt_dmabuf_import(void *arg) >> goto out_obj; >> } >> - err = dma_buf_vmap(dmabuf, &map); >> + err = dma_buf_vmap_unlocked(dmabuf, &map); >> dma_map = err ? NULL : map.vaddr; >> if (!dma_map) { >> pr_err("dma_buf_vmap failed\n"); >> @@ -337,7 +337,7 @@ static int igt_dmabuf_import(void *arg) >> err = 0; >> out_dma_map: >> - dma_buf_vunmap(dmabuf, &map); >> + dma_buf_vunmap_unlocked(dmabuf, &map); >> out_obj: >> i915_gem_object_put(obj); >> out_dmabuf: >> @@ -358,7 +358,7 @@ static int igt_dmabuf_import_ownership(void *arg) >> if (IS_ERR(dmabuf)) >> return PTR_ERR(dmabuf); >> - err = dma_buf_vmap(dmabuf, &map); >> + err = dma_buf_vmap_unlocked(dmabuf, &map); >> ptr = err ? NULL : map.vaddr; >> if (!ptr) { >> pr_err("dma_buf_vmap failed\n"); >> @@ -367,7 +367,7 @@ static int igt_dmabuf_import_ownership(void *arg) >> } >> memset(ptr, 0xc5, PAGE_SIZE); >> - dma_buf_vunmap(dmabuf, &map); >> + dma_buf_vunmap_unlocked(dmabuf, &map); >> obj = to_intel_bo(i915_gem_prime_import(&i915->drm, dmabuf)); >> if (IS_ERR(obj)) { >> @@ -418,7 +418,7 @@ static int igt_dmabuf_export_vmap(void *arg) >> } >> i915_gem_object_put(obj); >> - err = dma_buf_vmap(dmabuf, &map); >> + err = dma_buf_vmap_unlocked(dmabuf, &map); >> ptr = err ? NULL : map.vaddr; >> if (!ptr) { >> pr_err("dma_buf_vmap failed\n"); >> @@ -435,7 +435,7 @@ static int igt_dmabuf_export_vmap(void *arg) >> memset(ptr, 0xc5, dmabuf->size); >> err = 0; >> - dma_buf_vunmap(dmabuf, &map); >> + dma_buf_vunmap_unlocked(dmabuf, &map); >> out: >> dma_buf_put(dmabuf); >> return err; >
>-----Original Message----- >From: Dmitry Osipenko <dmitry.osipenko@collabora.com> >Sent: Wednesday, August 31, 2022 11:38 AM >To: David Airlie <airlied@linux.ie>; Gerd Hoffmann <kraxel@redhat.com>; >Gurchetan Singh <gurchetansingh@chromium.org>; Chia-I Wu ><olvaffe@gmail.com>; Daniel Vetter <daniel@ffwll.ch>; Daniel Almeida ><daniel.almeida@collabora.com>; Gert Wollny <gert.wollny@collabora.com>; >Gustavo Padovan <gustavo.padovan@collabora.com>; Daniel Stone ><daniel@fooishbar.org>; Tomeu Vizoso <tomeu.vizoso@collabora.com>; >Maarten Lankhorst <maarten.lankhorst@linux.intel.com>; Maxime Ripard ><mripard@kernel.org>; Thomas Zimmermann <tzimmermann@suse.de>; >Rob Clark <robdclark@gmail.com>; Sumit Semwal ><sumit.semwal@linaro.org>; Christian König <christian.koenig@amd.com>; >Pan, Xinhui <Xinhui.Pan@amd.com>; Thierry Reding ><thierry.reding@gmail.com>; Tomasz Figa <tfiga@chromium.org>; Marek >Szyprowski <m.szyprowski@samsung.com>; Mauro Carvalho Chehab ><mchehab@kernel.org>; Alex Deucher <alexander.deucher@amd.com>; Jani >Nikula <jani.nikula@linux.intel.com>; Joonas Lahtinen ><joonas.lahtinen@linux.intel.com>; Vivi, Rodrigo <rodrigo.vivi@intel.com>; >Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>; Thomas Hellström ><thomas_os@shipmail.org>; Qiang Yu <yuq825@gmail.com>; Srinivas >Kandagatla <srinivas.kandagatla@linaro.org>; Amol Maheshwari ><amahesh@qti.qualcomm.com>; Jason Gunthorpe <jgg@ziepe.ca>; Leon >Romanovsky <leon@kernel.org>; Gross, Jurgen <jgross@suse.com>; Stefano >Stabellini <sstabellini@kernel.org>; Oleksandr Tyshchenko ><oleksandr_tyshchenko@epam.com>; Tomi Valkeinen <tomba@kernel.org>; >Russell King <linux@armlinux.org.uk>; Lucas Stach <l.stach@pengutronix.de>; >Christian Gmeiner <christian.gmeiner@gmail.com> >Cc: dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; Dmitry >Osipenko <digetx@gmail.com>; linux-media@vger.kernel.org; linaro-mm- >sig@lists.linaro.org; amd-gfx@lists.freedesktop.org; intel- >gfx@lists.freedesktop.org; kernel@collabora.com; virtualization@lists.linux- >foundation.org; linux-rdma@vger.kernel.org; linux-arm- >msm@vger.kernel.org >Subject: [PATCH v4 06/21] drm/i915: Prepare to dynamic dma-buf locking >specification > >Prepare i915 driver to the common dynamic dma-buf locking convention >by starting to use the unlocked versions of dma-buf API functions >and handling cases where importer now holds the reservation lock. > >Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> >--- > drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 +- > drivers/gpu/drm/i915/gem/i915_gem_object.c | 12 ++++++++++++ > .../gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c | 16 ++++++++-------- > 3 files changed, 21 insertions(+), 9 deletions(-) > >diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >index f5062d0c6333..07eee1c09aaf 100644 >--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c >@@ -72,7 +72,7 @@ static int i915_gem_dmabuf_vmap(struct dma_buf >*dma_buf, > struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf); > void *vaddr; > >- vaddr = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB); >+ vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB); > if (IS_ERR(vaddr)) > return PTR_ERR(vaddr); > >diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c >b/drivers/gpu/drm/i915/gem/i915_gem_object.c >index 389e9f157ca5..7e2a9b02526c 100644 >--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >@@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >drm_i915_private *i915, > continue; > } > >+ /* >+ * dma_buf_unmap_attachment() requires reservation to be >+ * locked. The imported GEM shouldn't share reservation lock, >+ * so it's safe to take the lock. >+ */ >+ if (obj->base.import_attach) >+ i915_gem_object_lock(obj, NULL); There is a lot of stuff going here. Taking the lock may be premature... > __i915_gem_object_pages_fini(obj); The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where unmap_attachment is actually called, would it make more sense to make do the locking there? Mike >+ >+ if (obj->base.import_attach) >+ i915_gem_object_unlock(obj); >+ > __i915_gem_free_object(obj); > > /* But keep the pointer alive for RCU-protected lookups */ >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 62c61af77a42..9e3ed634aa0e 100644 >--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c >+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c >@@ -213,7 +213,7 @@ static int igt_dmabuf_import_same_driver(struct >drm_i915_private *i915, > goto out_import; > } > >- st = dma_buf_map_attachment(import_attach, >DMA_BIDIRECTIONAL); >+ st = dma_buf_map_attachment_unlocked(import_attach, >DMA_BIDIRECTIONAL); > if (IS_ERR(st)) { > err = PTR_ERR(st); > goto out_detach; >@@ -226,7 +226,7 @@ static int igt_dmabuf_import_same_driver(struct >drm_i915_private *i915, > timeout = -ETIME; > } > err = timeout > 0 ? 0 : timeout; >- dma_buf_unmap_attachment(import_attach, st, >DMA_BIDIRECTIONAL); >+ dma_buf_unmap_attachment_unlocked(import_attach, st, >DMA_BIDIRECTIONAL); > out_detach: > dma_buf_detach(dmabuf, import_attach); > out_import: >@@ -296,7 +296,7 @@ static int igt_dmabuf_import(void *arg) > goto out_obj; > } > >- err = dma_buf_vmap(dmabuf, &map); >+ err = dma_buf_vmap_unlocked(dmabuf, &map); > dma_map = err ? NULL : map.vaddr; > if (!dma_map) { > pr_err("dma_buf_vmap failed\n"); >@@ -337,7 +337,7 @@ static int igt_dmabuf_import(void *arg) > > err = 0; > out_dma_map: >- dma_buf_vunmap(dmabuf, &map); >+ dma_buf_vunmap_unlocked(dmabuf, &map); > out_obj: > i915_gem_object_put(obj); > out_dmabuf: >@@ -358,7 +358,7 @@ static int igt_dmabuf_import_ownership(void *arg) > if (IS_ERR(dmabuf)) > return PTR_ERR(dmabuf); > >- err = dma_buf_vmap(dmabuf, &map); >+ err = dma_buf_vmap_unlocked(dmabuf, &map); > ptr = err ? NULL : map.vaddr; > if (!ptr) { > pr_err("dma_buf_vmap failed\n"); >@@ -367,7 +367,7 @@ static int igt_dmabuf_import_ownership(void *arg) > } > > memset(ptr, 0xc5, PAGE_SIZE); >- dma_buf_vunmap(dmabuf, &map); >+ dma_buf_vunmap_unlocked(dmabuf, &map); > > obj = to_intel_bo(i915_gem_prime_import(&i915->drm, dmabuf)); > if (IS_ERR(obj)) { >@@ -418,7 +418,7 @@ static int igt_dmabuf_export_vmap(void *arg) > } > i915_gem_object_put(obj); > >- err = dma_buf_vmap(dmabuf, &map); >+ err = dma_buf_vmap_unlocked(dmabuf, &map); > ptr = err ? NULL : map.vaddr; > if (!ptr) { > pr_err("dma_buf_vmap failed\n"); >@@ -435,7 +435,7 @@ static int igt_dmabuf_export_vmap(void *arg) > memset(ptr, 0xc5, dmabuf->size); > > err = 0; >- dma_buf_vunmap(dmabuf, &map); >+ dma_buf_vunmap_unlocked(dmabuf, &map); > out: > dma_buf_put(dmabuf); > return err; >-- >2.37.2
01.09.2022 17:02, Ruhl, Michael J пишет: ... >> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >> drm_i915_private *i915, >> continue; >> } >> >> + /* >> + * dma_buf_unmap_attachment() requires reservation to be >> + * locked. The imported GEM shouldn't share reservation lock, >> + * so it's safe to take the lock. >> + */ >> + if (obj->base.import_attach) >> + i915_gem_object_lock(obj, NULL); > > There is a lot of stuff going here. Taking the lock may be premature... > >> __i915_gem_object_pages_fini(obj); > > The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where > unmap_attachment is actually called, would it make more sense to make > do the locking there? The __i915_gem_object_put_pages() is invoked with a held reservation lock, while freeing object is a special time when we know that GEM is unused. The __i915_gem_free_objects() was taking the lock two weeks ago until the change made Chris Wilson [1] reached linux-next. [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=2826d447fbd60e6a05e53d5f918bceb8c04e315c I don't think we can take the lock within i915_gem_object_put_pages_dmabuf(), it may/should deadlock other code paths.
02.09.2022 13:31, Dmitry Osipenko пишет: > 01.09.2022 17:02, Ruhl, Michael J пишет: > ... >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >>> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >>> drm_i915_private *i915, >>> continue; >>> } >>> >>> + /* >>> + * dma_buf_unmap_attachment() requires reservation to be >>> + * locked. The imported GEM shouldn't share reservation lock, >>> + * so it's safe to take the lock. >>> + */ >>> + if (obj->base.import_attach) >>> + i915_gem_object_lock(obj, NULL); >> >> There is a lot of stuff going here. Taking the lock may be premature... >> >>> __i915_gem_object_pages_fini(obj); >> >> The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where >> unmap_attachment is actually called, would it make more sense to make >> do the locking there? > > The __i915_gem_object_put_pages() is invoked with a held reservation > lock, while freeing object is a special time when we know that GEM is > unused. > > The __i915_gem_free_objects() was taking the lock two weeks ago until > the change made Chris Wilson [1] reached linux-next. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=2826d447fbd60e6a05e53d5f918bceb8c04e315c > > I don't think we can take the lock within > i915_gem_object_put_pages_dmabuf(), it may/should deadlock other code paths. On the other hand, we can check whether the GEM's refcount number is zero in i915_gem_object_put_pages_dmabuf() and then take the lock if it's zero. Also, seems it should be possible just to bail out from i915_gem_object_put_pages_dmabuf() if refcount=0. The further drm_prime_gem_destroy() will take care of unmapping. Perhaps this could be the best option, I'll give it a test.
>-----Original Message----- >From: Dmitry Osipenko <digetx@gmail.com> >Sent: Friday, September 2, 2022 6:39 AM >To: Ruhl, Michael J <michael.j.ruhl@intel.com>; Dmitry Osipenko ><dmitry.osipenko@collabora.com>; Jani Nikula <jani.nikula@linux.intel.com>; >Joonas Lahtinen <joonas.lahtinen@linux.intel.com>; Vivi, Rodrigo ><rodrigo.vivi@intel.com>; Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>; >Thomas Hellström <thomas_os@shipmail.org>; Christian König ><christian.koenig@amd.com>; Chris Wilson <chris@chris-wilson.co.uk> >Cc: dri-devel@lists.freedesktop.org; linux-kernel@vger.kernel.org; linux- >media@vger.kernel.org; linaro-mm-sig@lists.linaro.org; amd- >gfx@lists.freedesktop.org; intel-gfx@lists.freedesktop.org; >kernel@collabora.com; virtualization@lists.linux-foundation.org; linux- >rdma@vger.kernel.org; linux-arm-msm@vger.kernel.org; David Airlie ><airlied@linux.ie>; Gerd Hoffmann <kraxel@redhat.com>; Gurchetan Singh ><gurchetansingh@chromium.org>; Chia-I Wu <olvaffe@gmail.com>; Daniel >Vetter <daniel@ffwll.ch>; Daniel Almeida <daniel.almeida@collabora.com>; >Gert Wollny <gert.wollny@collabora.com>; Gustavo Padovan ><gustavo.padovan@collabora.com>; Daniel Stone <daniel@fooishbar.org>; >Tomeu Vizoso <tomeu.vizoso@collabora.com>; Maarten Lankhorst ><maarten.lankhorst@linux.intel.com>; Maxime Ripard ><mripard@kernel.org>; Thomas Zimmermann <tzimmermann@suse.de>; >Rob Clark <robdclark@gmail.com>; Sumit Semwal ><sumit.semwal@linaro.org>; Pan, Xinhui <Xinhui.Pan@amd.com>; Thierry >Reding <thierry.reding@gmail.com>; Tomasz Figa <tfiga@chromium.org>; >Marek Szyprowski <m.szyprowski@samsung.com>; Mauro Carvalho Chehab ><mchehab@kernel.org>; Alex Deucher <alexander.deucher@amd.com>; >Qiang Yu <yuq825@gmail.com>; Srinivas Kandagatla ><srinivas.kandagatla@linaro.org>; Amol Maheshwari ><amahesh@qti.qualcomm.com>; Jason Gunthorpe <jgg@ziepe.ca>; Leon >Romanovsky <leon@kernel.org>; Gross, Jurgen <jgross@suse.com>; Stefano >Stabellini <sstabellini@kernel.org>; Oleksandr Tyshchenko ><oleksandr_tyshchenko@epam.com>; Tomi Valkeinen <tomba@kernel.org>; >Russell King <linux@armlinux.org.uk>; Lucas Stach <l.stach@pengutronix.de>; >Christian Gmeiner <christian.gmeiner@gmail.com> >Subject: Re: [PATCH v4 06/21] drm/i915: Prepare to dynamic dma-buf locking >specification > >02.09.2022 13:31, Dmitry Osipenko пишет: >> 01.09.2022 17:02, Ruhl, Michael J пишет: >> ... >>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >>>> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >>>> drm_i915_private *i915, >>>> continue; >>>> } >>>> >>>> + /* >>>> + * dma_buf_unmap_attachment() requires reservation to be >>>> + * locked. The imported GEM shouldn't share reservation lock, >>>> + * so it's safe to take the lock. >>>> + */ >>>> + if (obj->base.import_attach) >>>> + i915_gem_object_lock(obj, NULL); >>> >>> There is a lot of stuff going here. Taking the lock may be premature... >>> >>>> __i915_gem_object_pages_fini(obj); >>> >>> The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where >>> unmap_attachment is actually called, would it make more sense to make >>> do the locking there? >> >> The __i915_gem_object_put_pages() is invoked with a held reservation >> lock, while freeing object is a special time when we know that GEM is >> unused. >> >> The __i915_gem_free_objects() was taking the lock two weeks ago until >> the change made Chris Wilson [1] reached linux-next. >> >> [1] >> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux- >next.git/commit/?id=2826d447fbd60e6a05e53d5f918bceb8c04e315c >> >> I don't think we can take the lock within >> i915_gem_object_put_pages_dmabuf(), it may/should deadlock other code >paths. > >On the other hand, we can check whether the GEM's refcount number is >zero in i915_gem_object_put_pages_dmabuf() and then take the lock if >it's zero. > >Also, seems it should be possible just to bail out from >i915_gem_object_put_pages_dmabuf() if refcount=0. The further >drm_prime_gem_destroy() will take care of unmapping. Perhaps this could >be the best option, I'll give it a test. i915_gem_object_put_pages() is uses the SG, and the usage for drm_prim_gem_destroy() from __i915_gem_free_objects() doesn't use the SG because it has been "freed" already, I am not sure if that would work... Hmm.. with that in mind, maybe moving the base.import_attach check to __i915_gem_object_put_pages with your attach check? atomic_set(&obj->mm.pages_pin_count, 0); if (obj->base.import) i915_gem_object_lock(obj, NULL); __i915_gem_object_put_pages(obj); if (obj->base.import) i915_gem_object_unlock(obj, NULL); GEM_BUG_ON(i915_gem_object_has_pages(obj)); Pretty much one step up from the dmabuf interface, but we are guaranteed to not have any pinned pages? The other caller of __i915_gem_object_pages_fini is the i915_ttm move_notify which should not conflict (export side, not import side). Since it appears that not locking during the clean up is desirable, trying to make sure take the lock is taken at the last moment might be the right path? M
On 9/2/22 19:26, Ruhl, Michael J wrote: >> 02.09.2022 13:31, Dmitry Osipenko пишет: >>> 01.09.2022 17:02, Ruhl, Michael J пишет: >>> ... >>>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c >>>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c >>>>> @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct >>>>> drm_i915_private *i915, >>>>> continue; >>>>> } >>>>> >>>>> + /* >>>>> + * dma_buf_unmap_attachment() requires reservation to be >>>>> + * locked. The imported GEM shouldn't share reservation lock, >>>>> + * so it's safe to take the lock. >>>>> + */ >>>>> + if (obj->base.import_attach) >>>>> + i915_gem_object_lock(obj, NULL); >>>> >>>> There is a lot of stuff going here. Taking the lock may be premature... >>>> >>>>> __i915_gem_object_pages_fini(obj); >>>> >>>> The i915_gem_dmabuf.c:i915_gem_object_put_pages_dmabuf is where >>>> unmap_attachment is actually called, would it make more sense to make >>>> do the locking there? >>> >>> The __i915_gem_object_put_pages() is invoked with a held reservation >>> lock, while freeing object is a special time when we know that GEM is >>> unused. >>> >>> The __i915_gem_free_objects() was taking the lock two weeks ago until >>> the change made Chris Wilson [1] reached linux-next. >>> >>> [1] >>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux- >> next.git/commit/?id=2826d447fbd60e6a05e53d5f918bceb8c04e315c >>> >>> I don't think we can take the lock within >>> i915_gem_object_put_pages_dmabuf(), it may/should deadlock other code >> paths. >> >> On the other hand, we can check whether the GEM's refcount number is >> zero in i915_gem_object_put_pages_dmabuf() and then take the lock if >> it's zero. >> >> Also, seems it should be possible just to bail out from >> i915_gem_object_put_pages_dmabuf() if refcount=0. The further >> drm_prime_gem_destroy() will take care of unmapping. Perhaps this could >> be the best option, I'll give it a test. > > i915_gem_object_put_pages() is uses the SG, and the usage for > drm_prim_gem_destroy() > > from __i915_gem_free_objects() doesn't use the SG because it has been "freed" > already, I am not sure if that would work... > > Hmm.. with that in mind, maybe moving the base.import_attach check to > __i915_gem_object_put_pages with your attach check? I see you meant __i915_gem_object_pages_fini() here. > atomic_set(&obj->mm.pages_pin_count, 0); > if (obj->base.import) > i915_gem_object_lock(obj, NULL); > > __i915_gem_object_put_pages(obj); > > if (obj->base.import) > i915_gem_object_unlock(obj, NULL); > GEM_BUG_ON(i915_gem_object_has_pages(obj)); > > Pretty much one step up from the dmabuf interface, but we are guaranteed to > not have any pinned pages? Importer shouldn't hold pages outside of dma-buf API, otherwise it should be a bug. > The other caller of __i915_gem_object_pages_fini is the i915_ttm move_notify > which should not conflict (export side, not import side). > > Since it appears that not locking during the clean up is desirable, trying to make sure take the lock > is taken at the last moment might be the right path? Reducing the scope of locking usually is preferred more. Yours suggestion works okay, I couldn't spot any problems at least for a non-TTM code paths. It's indeed a bit not nice that __i915_gem_object_pages_fini() is used by TTM, but should be safe for imported objects. Will be great if anyone from i915 maintainers could ack this variant.
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c index f5062d0c6333..07eee1c09aaf 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c @@ -72,7 +72,7 @@ static int i915_gem_dmabuf_vmap(struct dma_buf *dma_buf, struct drm_i915_gem_object *obj = dma_buf_to_obj(dma_buf); void *vaddr; - vaddr = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB); + vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB); if (IS_ERR(vaddr)) return PTR_ERR(vaddr); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c index 389e9f157ca5..7e2a9b02526c 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -331,7 +331,19 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915, continue; } + /* + * dma_buf_unmap_attachment() requires reservation to be + * locked. The imported GEM shouldn't share reservation lock, + * so it's safe to take the lock. + */ + if (obj->base.import_attach) + i915_gem_object_lock(obj, NULL); + __i915_gem_object_pages_fini(obj); + + if (obj->base.import_attach) + i915_gem_object_unlock(obj); + __i915_gem_free_object(obj); /* But keep the pointer alive for RCU-protected lookups */ 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 62c61af77a42..9e3ed634aa0e 100644 --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c @@ -213,7 +213,7 @@ static int igt_dmabuf_import_same_driver(struct drm_i915_private *i915, goto out_import; } - st = dma_buf_map_attachment(import_attach, DMA_BIDIRECTIONAL); + st = dma_buf_map_attachment_unlocked(import_attach, DMA_BIDIRECTIONAL); if (IS_ERR(st)) { err = PTR_ERR(st); goto out_detach; @@ -226,7 +226,7 @@ static int igt_dmabuf_import_same_driver(struct drm_i915_private *i915, timeout = -ETIME; } err = timeout > 0 ? 0 : timeout; - dma_buf_unmap_attachment(import_attach, st, DMA_BIDIRECTIONAL); + dma_buf_unmap_attachment_unlocked(import_attach, st, DMA_BIDIRECTIONAL); out_detach: dma_buf_detach(dmabuf, import_attach); out_import: @@ -296,7 +296,7 @@ static int igt_dmabuf_import(void *arg) goto out_obj; } - err = dma_buf_vmap(dmabuf, &map); + err = dma_buf_vmap_unlocked(dmabuf, &map); dma_map = err ? NULL : map.vaddr; if (!dma_map) { pr_err("dma_buf_vmap failed\n"); @@ -337,7 +337,7 @@ static int igt_dmabuf_import(void *arg) err = 0; out_dma_map: - dma_buf_vunmap(dmabuf, &map); + dma_buf_vunmap_unlocked(dmabuf, &map); out_obj: i915_gem_object_put(obj); out_dmabuf: @@ -358,7 +358,7 @@ static int igt_dmabuf_import_ownership(void *arg) if (IS_ERR(dmabuf)) return PTR_ERR(dmabuf); - err = dma_buf_vmap(dmabuf, &map); + err = dma_buf_vmap_unlocked(dmabuf, &map); ptr = err ? NULL : map.vaddr; if (!ptr) { pr_err("dma_buf_vmap failed\n"); @@ -367,7 +367,7 @@ static int igt_dmabuf_import_ownership(void *arg) } memset(ptr, 0xc5, PAGE_SIZE); - dma_buf_vunmap(dmabuf, &map); + dma_buf_vunmap_unlocked(dmabuf, &map); obj = to_intel_bo(i915_gem_prime_import(&i915->drm, dmabuf)); if (IS_ERR(obj)) { @@ -418,7 +418,7 @@ static int igt_dmabuf_export_vmap(void *arg) } i915_gem_object_put(obj); - err = dma_buf_vmap(dmabuf, &map); + err = dma_buf_vmap_unlocked(dmabuf, &map); ptr = err ? NULL : map.vaddr; if (!ptr) { pr_err("dma_buf_vmap failed\n"); @@ -435,7 +435,7 @@ static int igt_dmabuf_export_vmap(void *arg) memset(ptr, 0xc5, dmabuf->size); err = 0; - dma_buf_vunmap(dmabuf, &map); + dma_buf_vunmap_unlocked(dmabuf, &map); out: dma_buf_put(dmabuf); return err;
Prepare i915 driver to the common dynamic dma-buf locking convention by starting to use the unlocked versions of dma-buf API functions and handling cases where importer now holds the reservation lock. Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> --- drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 +- drivers/gpu/drm/i915/gem/i915_gem_object.c | 12 ++++++++++++ .../gpu/drm/i915/gem/selftests/i915_gem_dmabuf.c | 16 ++++++++-------- 3 files changed, 21 insertions(+), 9 deletions(-)