[PATCH v4 0/6] Move dma-buf mmap() reservation locking down to exporters

[PATCH v4 0/6] Move dma-buf mmap() reservation locking down to exporters

[Dmitry Osipenko]

This patchset makes dma-buf exporters responisble for taking care of
the reservation lock. I also included patch that moves drm-shmem to use
reservation lock, to let CI test the whole set. I'm going to take all
the patches via the drm-misc tree, please give an ack.

Previous policy stated that dma-buf core takes the lock around mmap()
callback. Which meant that both importers and exporters shouldn't touch
the reservation lock in the mmap() code path. This worked well until
Intel-CI found a deadlock problem in a case of self-imported dma-buf [1].

The problem happens when userpace mmaps a self-imported dma-buf, i.e.
mmaps the dma-buf FD. DRM core treats self-imported dma-bufs as own GEMs
[2]. There is no way to differentiate a prime GEM from a normal GEM for
drm-shmem in drm_gem_shmem_mmap(), which resulted in a deadlock problem
for drm-shmem mmap() code path once it's switched to use reservation lock.

It was difficult to fix the drm-shmem problem without adjusting dma-buf
locking policy. In parctice not much changed from importers perspective
because previosly dma-buf was taking the lock in between of importers
and exporters. Now this lock is shifted down to exporters.

[1] https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_114671v2/shard-snb5/igt@prime_vgem@sync@rcs0.html
[2] https://elixir.bootlin.com/linux/v6.3-rc4/source/drivers/gpu/drm/drm_prime.c#L924

Changelog:

v4: - Added dma_resv_assert_held() to drm_gem_shmem_get_pages(), making
      assert consistent with the put() variant. Suggested by Emil Velikov.

v3: - Added r-b from Hans Verkuil to the videobuf2 patch.

    - The v2 fastrpc patch was already applied, not including it anymore.
      Though, the cover-letter says that I'd want to apply all the patches
      via the drm-misc tree to keep the proper ordering of the changes.

    - Previously Intel's CI gave a flake failure to v2, want to re-test
      it again.

v2: - Added ack from Christian König to the DRM patch.

    - Dropped "fixes" tag from the patches, like was requested by
      Christian König. The patches don't actually need a backport
      and merely improve the locking policy.

    - Dropped "reverts" from the patch titles to prevent them from
      auto-backporting by the stable bot based on the title.

    - Added r-b from Emil Velikov and placed the drm_WARN in the
      drm-shmem patch like he suggested in a comment to v1.

    - Corrected drm-shmem patch dma_resv_lock(obj->resv) inconsistently
      used with dma_resv_unlock(shmem->base.resv). Now shmem->base.resv
      variant is used for all locks/unlocks.

Dmitry Osipenko (6):
  media: videobuf2: Don't assert held reservation lock for dma-buf
    mmapping
  dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping
  udmabuf: Don't assert held reservation lock for dma-buf mmapping
  drm: Don't assert held reservation lock for dma-buf mmapping
  dma-buf: Change locking policy for mmap()
  drm/shmem-helper: Switch to reservation lock

 drivers/dma-buf/dma-buf.c                     |  17 +-
 drivers/dma-buf/heaps/cma_heap.c              |   3 -
 drivers/dma-buf/heaps/system_heap.c           |   3 -
 drivers/dma-buf/udmabuf.c                     |   2 -
 drivers/gpu/drm/drm_gem_shmem_helper.c        | 210 ++++++++----------
 drivers/gpu/drm/drm_prime.c                   |   2 -
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    |   2 -
 drivers/gpu/drm/lima/lima_gem.c               |   8 +-
 drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c     |   2 -
 drivers/gpu/drm/panfrost/panfrost_drv.c       |   7 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   6 +-
 drivers/gpu/drm/panfrost/panfrost_mmu.c       |  19 +-
 drivers/gpu/drm/tegra/gem.c                   |   2 -
 .../common/videobuf2/videobuf2-dma-contig.c   |   3 -
 .../media/common/videobuf2/videobuf2-dma-sg.c |   3 -
 .../common/videobuf2/videobuf2-vmalloc.c      |   3 -
 include/drm/drm_gem_shmem_helper.h            |  14 +-
 17 files changed, 119 insertions(+), 187 deletions(-)

-- 
2.40.1

[PATCH v4 1/6] media: videobuf2: Don't assert held reservation lock for dma-buf mmapping

[Dmitry Osipenko]

Don't assert held dma-buf reservation lock on memory mapping of exported
buffer.

We're going to change dma-buf mmap() locking policy such that exporters
will have to handle the lock. The previous locking policy caused deadlock
problem for DRM drivers in a case of self-imported dma-bufs once these
drivers are moved to use reservation lock universally. The problem is
solved by moving the lock down to exporters. This patch prepares videobuf2
for the locking policy update.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/media/common/videobuf2/videobuf2-dma-contig.c | 3 ---
 drivers/media/common/videobuf2/videobuf2-dma-sg.c     | 3 ---
 drivers/media/common/videobuf2/videobuf2-vmalloc.c    | 3 ---
 3 files changed, 9 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
index 205d3cac425c..2fa455d4a048 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
@@ -11,7 +11,6 @@
  */
 
 #include <linux/dma-buf.h>
-#include <linux/dma-resv.h>
 #include <linux/module.h>
 #include <linux/refcount.h>
 #include <linux/scatterlist.h>
@@ -456,8 +455,6 @@ static int vb2_dc_dmabuf_ops_vmap(struct dma_buf *dbuf, struct iosys_map *map)
 static int vb2_dc_dmabuf_ops_mmap(struct dma_buf *dbuf,
 	struct vm_area_struct *vma)
 {
-	dma_resv_assert_held(dbuf->resv);
-
 	return vb2_dc_mmap(dbuf->priv, vma);
 }
 
diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
index 183037fb1273..28f3fdfe23a2 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
@@ -10,7 +10,6 @@
  * the Free Software Foundation.
  */
 
-#include <linux/dma-resv.h>
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/refcount.h>
@@ -498,8 +497,6 @@ static int vb2_dma_sg_dmabuf_ops_vmap(struct dma_buf *dbuf,
 static int vb2_dma_sg_dmabuf_ops_mmap(struct dma_buf *dbuf,
 	struct vm_area_struct *vma)
 {
-	dma_resv_assert_held(dbuf->resv);
-
 	return vb2_dma_sg_mmap(dbuf->priv, vma);
 }
 
diff --git a/drivers/media/common/videobuf2/videobuf2-vmalloc.c b/drivers/media/common/videobuf2/videobuf2-vmalloc.c
index a6c6d2fcaaa4..7c635e292106 100644
--- a/drivers/media/common/videobuf2/videobuf2-vmalloc.c
+++ b/drivers/media/common/videobuf2/videobuf2-vmalloc.c
@@ -10,7 +10,6 @@
  * the Free Software Foundation.
  */
 
-#include <linux/dma-resv.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/mm.h>
@@ -319,8 +318,6 @@ static int vb2_vmalloc_dmabuf_ops_vmap(struct dma_buf *dbuf,
 static int vb2_vmalloc_dmabuf_ops_mmap(struct dma_buf *dbuf,
 	struct vm_area_struct *vma)
 {
-	dma_resv_assert_held(dbuf->resv);
-
 	return vb2_vmalloc_mmap(dbuf->priv, vma);
 }
 
-- 
2.40.1

[PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping

[Dmitry Osipenko]

Don't assert held dma-buf reservation lock on memory mapping of exported
buffer.

We're going to change dma-buf mmap() locking policy such that exporters
will have to handle the lock. The previous locking policy caused deadlock
problem for DRM drivers in a case of self-imported dma-bufs once these
drivers are moved to use reservation lock universally. The problem
solved by moving the lock down to exporters. This patch prepares dma-buf
heaps for the locking policy update.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/dma-buf/heaps/cma_heap.c    | 3 ---
 drivers/dma-buf/heaps/system_heap.c | 3 ---
 2 files changed, 6 deletions(-)

diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index 1131fb943992..28fb04eccdd0 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -13,7 +13,6 @@
 #include <linux/dma-buf.h>
 #include <linux/dma-heap.h>
 #include <linux/dma-map-ops.h>
-#include <linux/dma-resv.h>
 #include <linux/err.h>
 #include <linux/highmem.h>
 #include <linux/io.h>
@@ -183,8 +182,6 @@ static int cma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 {
 	struct cma_heap_buffer *buffer = dmabuf->priv;
 
-	dma_resv_assert_held(dmabuf->resv);
-
 	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
 		return -EINVAL;
 
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index e8bd10e60998..fcf836ba9c1f 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -13,7 +13,6 @@
 #include <linux/dma-buf.h>
 #include <linux/dma-mapping.h>
 #include <linux/dma-heap.h>
-#include <linux/dma-resv.h>
 #include <linux/err.h>
 #include <linux/highmem.h>
 #include <linux/mm.h>
@@ -202,8 +201,6 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
 	struct sg_page_iter piter;
 	int ret;
 
-	dma_resv_assert_held(dmabuf->resv);
-
 	for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
 		struct page *page = sg_page_iter_page(&piter);
 
-- 
2.40.1

Re: [PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping

[T.J. Mercier]

On Mon, May 29, 2023 at 3:46 PM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Don't assert held dma-buf reservation lock on memory mapping of exported
> buffer.
>
> We're going to change dma-buf mmap() locking policy such that exporters
> will have to handle the lock. The previous locking policy caused deadlock
> problem for DRM drivers in a case of self-imported dma-bufs once these
> drivers are moved to use reservation lock universally. The problem
> solved by moving the lock down to exporters. This patch prepares dma-buf
> heaps for the locking policy update.
>
Hi Dmitry,

I see that in patch 6 of this series calls to
dma_resv_lock/dma_resv_unlock have been added to the
drm_gem_shmem_helper functions and some exporters. But I'm curious why
no dma_resv_lock/dma_resv_unlock calls were added to these two dma-buf
heap exporters for mmap?

Thanks,
T.J.

> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>  drivers/dma-buf/heaps/cma_heap.c    | 3 ---
>  drivers/dma-buf/heaps/system_heap.c | 3 ---
>  2 files changed, 6 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> index 1131fb943992..28fb04eccdd0 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -13,7 +13,6 @@
>  #include <linux/dma-buf.h>
>  #include <linux/dma-heap.h>
>  #include <linux/dma-map-ops.h>
> -#include <linux/dma-resv.h>
>  #include <linux/err.h>
>  #include <linux/highmem.h>
>  #include <linux/io.h>
> @@ -183,8 +182,6 @@ static int cma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
>  {
>         struct cma_heap_buffer *buffer = dmabuf->priv;
>
> -       dma_resv_assert_held(dmabuf->resv);
> -
>         if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
>                 return -EINVAL;
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index e8bd10e60998..fcf836ba9c1f 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -13,7 +13,6 @@
>  #include <linux/dma-buf.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/dma-heap.h>
> -#include <linux/dma-resv.h>
>  #include <linux/err.h>
>  #include <linux/highmem.h>
>  #include <linux/mm.h>
> @@ -202,8 +201,6 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
>         struct sg_page_iter piter;
>         int ret;
>
> -       dma_resv_assert_held(dmabuf->resv);
> -
>         for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
>                 struct page *page = sg_page_iter_page(&piter);
>
> --
> 2.40.1
>

Re: [PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping

[Dmitry Osipenko]

Hi,

On 6/21/23 20:21, T.J. Mercier wrote:
> On Mon, May 29, 2023 at 3:46 PM Dmitry Osipenko
> <dmitry.osipenko@collabora.com> wrote:
>>
>> Don't assert held dma-buf reservation lock on memory mapping of exported
>> buffer.
>>
>> We're going to change dma-buf mmap() locking policy such that exporters
>> will have to handle the lock. The previous locking policy caused deadlock
>> problem for DRM drivers in a case of self-imported dma-bufs once these
>> drivers are moved to use reservation lock universally. The problem
>> solved by moving the lock down to exporters. This patch prepares dma-buf
>> heaps for the locking policy update.
>>
> Hi Dmitry,
> 
> I see that in patch 6 of this series calls to
> dma_resv_lock/dma_resv_unlock have been added to the
> drm_gem_shmem_helper functions and some exporters. But I'm curious why
> no dma_resv_lock/dma_resv_unlock calls were added to these two dma-buf
> heap exporters for mmap?

DMA-buf heaps are exporters, drm_gem_shmem_helper is importer. Locking
rules are different for importers and exporters.

DMA-heaps use own locking, they can be moved to resv lock in the future.

DMA-heaps don't protect internal data in theirs mmap() implementations,
nothing to protect there.

-- 
Best regards,
Dmitry

Re: [PATCH v4 2/6] dma-buf/heaps: Don't assert held reservation lock for dma-buf mmapping

[T.J. Mercier]

On Wed, Jun 21, 2023 at 11:16 AM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Hi,
>
> On 6/21/23 20:21, T.J. Mercier wrote:
> > On Mon, May 29, 2023 at 3:46 PM Dmitry Osipenko
> > <dmitry.osipenko@collabora.com> wrote:
> >>
> >> Don't assert held dma-buf reservation lock on memory mapping of exported
> >> buffer.
> >>
> >> We're going to change dma-buf mmap() locking policy such that exporters
> >> will have to handle the lock. The previous locking policy caused deadlock
> >> problem for DRM drivers in a case of self-imported dma-bufs once these
> >> drivers are moved to use reservation lock universally. The problem
> >> solved by moving the lock down to exporters. This patch prepares dma-buf
> >> heaps for the locking policy update.
> >>
> > Hi Dmitry,
> >
> > I see that in patch 6 of this series calls to
> > dma_resv_lock/dma_resv_unlock have been added to the
> > drm_gem_shmem_helper functions and some exporters. But I'm curious why
> > no dma_resv_lock/dma_resv_unlock calls were added to these two dma-buf
> > heap exporters for mmap?
>
> DMA-buf heaps are exporters, drm_gem_shmem_helper is importer. Locking
> rules are different for importers and exporters.
>
> DMA-heaps use own locking, they can be moved to resv lock in the future.
>
> DMA-heaps don't protect internal data in theirs mmap() implementations,
> nothing to protect there.
>
Thanks.

[PATCH v4 3/6] udmabuf: Don't assert held reservation lock for dma-buf mmapping

[Dmitry Osipenko]

Don't assert held dma-buf reservation lock on memory mapping of exported
buffer.

We're going to change dma-buf mmap() locking policy such that exporters
will have to handle the lock. The previous locking policy caused deadlock
problem for DRM drivers in a case of self-imported dma-bufs once these
drivers are moved to use reservation lock universally. The problem is
solved by moving the lock down to exporters. This patch prepares udmabuf
for the locking policy update.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/dma-buf/udmabuf.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 740d6e426ee9..277f1afa9552 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -52,8 +52,6 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
 {
 	struct udmabuf *ubuf = buf->priv;
 
-	dma_resv_assert_held(buf->resv);
-
 	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
 		return -EINVAL;
 
-- 
2.40.1

[PATCH v4 4/6] drm: Don't assert held reservation lock for dma-buf mmapping

[Dmitry Osipenko]

Don't assert held dma-buf reservation lock on memory mapping of exported
buffer.

We're going to change dma-buf mmap() locking policy such that exporters
will have to handle the lock. The previous locking policy caused deadlock
problem for DRM drivers in a case of self-imported dma-bufs once these
drivers are moved to use reservation lock universally. The problem is
solved by moving the lock down to exporters. This patch prepares DRM
drivers for the locking policy update.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_prime.c                | 2 --
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 2 --
 drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c  | 2 --
 drivers/gpu/drm/tegra/gem.c                | 2 --
 4 files changed, 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 149cd4ff6a3b..cea85e84666f 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -781,8 +781,6 @@ int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma)
 	struct drm_gem_object *obj = dma_buf->priv;
 	struct drm_device *dev = obj->dev;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	if (!dev->driver->gem_prime_mmap)
 		return -ENOSYS;
 
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index fd556a076d05..1df74f7aa3dc 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -97,8 +97,6 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int ret;
 
-	dma_resv_assert_held(dma_buf->resv);
-
 	if (obj->base.size < vma->vm_end - vma->vm_start)
 		return -EINVAL;
 
diff --git a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
index 3abc47521b2c..8e194dbc9506 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem_dmabuf.c
@@ -66,8 +66,6 @@ static int omap_gem_dmabuf_mmap(struct dma_buf *buffer,
 	struct drm_gem_object *obj = buffer->priv;
 	int ret = 0;
 
-	dma_resv_assert_held(buffer->resv);
-
 	ret = drm_gem_mmap_obj(obj, omap_gem_mmap_size(obj), vma);
 	if (ret < 0)
 		return ret;
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index bce991a2ccc0..871ef5d26523 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -693,8 +693,6 @@ static int tegra_gem_prime_mmap(struct dma_buf *buf, struct vm_area_struct *vma)
 	struct drm_gem_object *gem = buf->priv;
 	int err;
 
-	dma_resv_assert_held(buf->resv);
-
 	err = drm_gem_mmap_obj(gem, gem->size, vma);
 	if (err < 0)
 		return err;
-- 
2.40.1

[PATCH v4 5/6] dma-buf: Change locking policy for mmap()

[Dmitry Osipenko]

Change locking policy of mmap() callback, making exporters responsible
for handling dma-buf reservation locking. Previous locking policy stated
that dma-buf is locked for both importers and exporters by the dma-buf
core, which caused a deadlock problem for DRM drivers in a case of
self-imported dma-bufs which required to take the lock from the DRM
exporter side.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/dma-buf/dma-buf.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index aa4ea8530cb3..21916bba77d5 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -131,7 +131,6 @@ static struct file_system_type dma_buf_fs_type = {
 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;
-	int ret;
 
 	if (!is_dma_buf_file(file))
 		return -EINVAL;
@@ -147,11 +146,7 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;
 
-	dma_resv_lock(dmabuf->resv, NULL);
-	ret = dmabuf->ops->mmap(dmabuf, vma);
-	dma_resv_unlock(dmabuf->resv);
-
-	return ret;
+	return dmabuf->ops->mmap(dmabuf, vma);
 }
 
 static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
@@ -850,6 +845,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
  *     - &dma_buf_ops.release()
  *     - &dma_buf_ops.begin_cpu_access()
  *     - &dma_buf_ops.end_cpu_access()
+ *     - &dma_buf_ops.mmap()
  *
  * 2. These &dma_buf_ops callbacks are invoked with locked dma-buf
  *    reservation and exporter can't take the lock:
@@ -858,7 +854,6 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
  *     - &dma_buf_ops.unpin()
  *     - &dma_buf_ops.map_dma_buf()
  *     - &dma_buf_ops.unmap_dma_buf()
- *     - &dma_buf_ops.mmap()
  *     - &dma_buf_ops.vmap()
  *     - &dma_buf_ops.vunmap()
  *
@@ -1463,8 +1458,6 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		 unsigned long pgoff)
 {
-	int ret;
-
 	if (WARN_ON(!dmabuf || !vma))
 		return -EINVAL;
 
@@ -1485,11 +1478,7 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 	vma_set_file(vma, dmabuf->file);
 	vma->vm_pgoff = pgoff;
 
-	dma_resv_lock(dmabuf->resv, NULL);
-	ret = dmabuf->ops->mmap(dmabuf, vma);
-	dma_resv_unlock(dmabuf->resv);
-
-	return ret;
+	return dmabuf->ops->mmap(dmabuf, vma);
 }
 EXPORT_SYMBOL_NS_GPL(dma_buf_mmap, DMA_BUF);
 
-- 
2.40.1

Re: [PATCH v4 5/6] dma-buf: Change locking policy for mmap()

[Dmitry Osipenko]

On 5/31/23 22:58, Dmitry Osipenko wrote:
> On 5/30/23 01:39, Dmitry Osipenko wrote:
>> Change locking policy of mmap() callback, making exporters responsible
>> for handling dma-buf reservation locking. Previous locking policy stated
>> that dma-buf is locked for both importers and exporters by the dma-buf
>> core, which caused a deadlock problem for DRM drivers in a case of
>> self-imported dma-bufs which required to take the lock from the DRM
>> exporter side.
>>
>> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>> ---
>>  drivers/dma-buf/dma-buf.c | 17 +++--------------
>>  1 file changed, 3 insertions(+), 14 deletions(-)
> 
> Christian, you acked the drm patch of this series sometime ago, perhaps
> it also implies implicit ack to this patch, but I'd prefer to have the
> explicit ack. I'll apply this series to drm-misc later this week if
> you'll approve this dma-buf change. Thanks in advance!

I'll merge the patches tomorrow. If there are any additional comments,
then please don't hesitate to post them.

-- 
Best regards,
Dmitry

Re: [PATCH v4 5/6] dma-buf: Change locking policy for mmap()

[Christian König]

Am 20.06.23 um 17:58 schrieb Dmitry Osipenko:
> On 5/31/23 22:58, Dmitry Osipenko wrote:
>> On 5/30/23 01:39, Dmitry Osipenko wrote:
>>> Change locking policy of mmap() callback, making exporters responsible
>>> for handling dma-buf reservation locking. Previous locking policy stated
>>> that dma-buf is locked for both importers and exporters by the dma-buf
>>> core, which caused a deadlock problem for DRM drivers in a case of
>>> self-imported dma-bufs which required to take the lock from the DRM
>>> exporter side.
>>>
>>> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>> ---
>>>   drivers/dma-buf/dma-buf.c | 17 +++--------------
>>>   1 file changed, 3 insertions(+), 14 deletions(-)
>> Christian, you acked the drm patch of this series sometime ago, perhaps
>> it also implies implicit ack to this patch, but I'd prefer to have the
>> explicit ack. I'll apply this series to drm-misc later this week if
>> you'll approve this dma-buf change. Thanks in advance!
> I'll merge the patches tomorrow. If there are any additional comments,
> then please don't hesitate to post them.

Sorry for not responding earlier, I have been moving both my office as 
well as my household and still catching up.

I don't have time for an in-deep review, but my ack stands for the whole 
series.

Regards,
Christian.

Re: [PATCH v4 5/6] dma-buf: Change locking policy for mmap()

[Dmitry Osipenko]

On 6/21/23 08:42, Christian König wrote:
> Am 20.06.23 um 17:58 schrieb Dmitry Osipenko:
>> On 5/31/23 22:58, Dmitry Osipenko wrote:
>>> On 5/30/23 01:39, Dmitry Osipenko wrote:
>>>> Change locking policy of mmap() callback, making exporters responsible
>>>> for handling dma-buf reservation locking. Previous locking policy
>>>> stated
>>>> that dma-buf is locked for both importers and exporters by the dma-buf
>>>> core, which caused a deadlock problem for DRM drivers in a case of
>>>> self-imported dma-bufs which required to take the lock from the DRM
>>>> exporter side.
>>>>
>>>> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>>> ---
>>>>   drivers/dma-buf/dma-buf.c | 17 +++--------------
>>>>   1 file changed, 3 insertions(+), 14 deletions(-)
>>> Christian, you acked the drm patch of this series sometime ago, perhaps
>>> it also implies implicit ack to this patch, but I'd prefer to have the
>>> explicit ack. I'll apply this series to drm-misc later this week if
>>> you'll approve this dma-buf change. Thanks in advance!
>> I'll merge the patches tomorrow. If there are any additional comments,
>> then please don't hesitate to post them.
> 
> Sorry for not responding earlier, I have been moving both my office as
> well as my household and still catching up.
> 
> I don't have time for an in-deep review, but my ack stands for the whole
> series.

Thanks! I'll add yours ack and merge patches soon

-- 
Best regards,
Dmitry

[PATCH v4 6/6] drm/shmem-helper: Switch to reservation lock

[Dmitry Osipenko]

Replace all drm-shmem locks with a GEM reservation lock. This makes locks
consistent with dma-buf locking convention where importers are responsible
for holding reservation lock for all operations performed over dma-bufs,
preventing deadlock between dma-buf importers and exporters.

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c        | 210 ++++++++----------
 drivers/gpu/drm/lima/lima_gem.c               |   8 +-
 drivers/gpu/drm/panfrost/panfrost_drv.c       |   7 +-
 .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   6 +-
 drivers/gpu/drm/panfrost/panfrost_mmu.c       |  19 +-
 include/drm/drm_gem_shmem_helper.h            |  14 +-
 6 files changed, 116 insertions(+), 148 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 4ea6507a77e5..a783d2245599 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -88,8 +88,6 @@ __drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
 	if (ret)
 		goto err_release;
 
-	mutex_init(&shmem->pages_lock);
-	mutex_init(&shmem->vmap_lock);
 	INIT_LIST_HEAD(&shmem->madv_list);
 
 	if (!private) {
@@ -141,11 +139,13 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
 
-	drm_WARN_ON(obj->dev, shmem->vmap_use_count);
-
 	if (obj->import_attach) {
 		drm_prime_gem_destroy(obj, shmem->sgt);
 	} else {
+		dma_resv_lock(shmem->base.resv, NULL);
+
+		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
+
 		if (shmem->sgt) {
 			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
 					  DMA_BIDIRECTIONAL, 0);
@@ -154,22 +154,24 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 		}
 		if (shmem->pages)
 			drm_gem_shmem_put_pages(shmem);
-	}
 
-	drm_WARN_ON(obj->dev, shmem->pages_use_count);
+		drm_WARN_ON(obj->dev, shmem->pages_use_count);
+
+		dma_resv_unlock(shmem->base.resv);
+	}
 
 	drm_gem_object_release(obj);
-	mutex_destroy(&shmem->pages_lock);
-	mutex_destroy(&shmem->vmap_lock);
 	kfree(shmem);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_free);
 
-static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
+static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
 	struct page **pages;
 
+	dma_resv_assert_held(shmem->base.resv);
+
 	if (shmem->pages_use_count++ > 0)
 		return 0;
 
@@ -197,35 +199,16 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
 }
 
 /*
- * drm_gem_shmem_get_pages - Allocate backing pages for a shmem GEM object
+ * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
  * @shmem: shmem GEM object
  *
- * This function makes sure that backing pages exists for the shmem GEM object
- * and increases the use count.
- *
- * Returns:
- * 0 on success or a negative error code on failure.
+ * This function decreases the use count and puts the backing pages when use drops to zero.
  */
-int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
+void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
-	int ret;
 
-	drm_WARN_ON(obj->dev, obj->import_attach);
-
-	ret = mutex_lock_interruptible(&shmem->pages_lock);
-	if (ret)
-		return ret;
-	ret = drm_gem_shmem_get_pages_locked(shmem);
-	mutex_unlock(&shmem->pages_lock);
-
-	return ret;
-}
-EXPORT_SYMBOL(drm_gem_shmem_get_pages);
-
-static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
-{
-	struct drm_gem_object *obj = &shmem->base;
+	dma_resv_assert_held(shmem->base.resv);
 
 	if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
 		return;
@@ -243,20 +226,25 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
 			  shmem->pages_mark_accessed_on_put);
 	shmem->pages = NULL;
 }
+EXPORT_SYMBOL(drm_gem_shmem_put_pages);
 
-/*
- * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
- * @shmem: shmem GEM object
- *
- * This function decreases the use count and puts the backing pages when use drops to zero.
- */
-void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
+static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 {
-	mutex_lock(&shmem->pages_lock);
-	drm_gem_shmem_put_pages_locked(shmem);
-	mutex_unlock(&shmem->pages_lock);
+	int ret;
+
+	dma_resv_assert_held(shmem->base.resv);
+
+	ret = drm_gem_shmem_get_pages(shmem);
+
+	return ret;
+}
+
+static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
+{
+	dma_resv_assert_held(shmem->base.resv);
+
+	drm_gem_shmem_put_pages(shmem);
 }
-EXPORT_SYMBOL(drm_gem_shmem_put_pages);
 
 /**
  * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
@@ -271,10 +259,17 @@ EXPORT_SYMBOL(drm_gem_shmem_put_pages);
 int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
+	int ret;
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
-	return drm_gem_shmem_get_pages(shmem);
+	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
+	if (ret)
+		return ret;
+	ret = drm_gem_shmem_pin_locked(shmem);
+	dma_resv_unlock(shmem->base.resv);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_gem_shmem_pin);
 
@@ -291,12 +286,29 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
-	drm_gem_shmem_put_pages(shmem);
+	dma_resv_lock(shmem->base.resv, NULL);
+	drm_gem_shmem_unpin_locked(shmem);
+	dma_resv_unlock(shmem->base.resv);
 }
 EXPORT_SYMBOL(drm_gem_shmem_unpin);
 
-static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
-				     struct iosys_map *map)
+/*
+ * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
+ * @shmem: shmem GEM object
+ * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
+ *       store.
+ *
+ * This function makes sure that a contiguous kernel virtual address mapping
+ * exists for the buffer backing the shmem GEM object. It hides the differences
+ * between dma-buf imported and natively allocated objects.
+ *
+ * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
+		       struct iosys_map *map)
 {
 	struct drm_gem_object *obj = &shmem->base;
 	int ret = 0;
@@ -312,6 +324,8 @@ static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 	} else {
 		pgprot_t prot = PAGE_KERNEL;
 
+		dma_resv_assert_held(shmem->base.resv);
+
 		if (shmem->vmap_use_count++ > 0) {
 			iosys_map_set_vaddr(map, shmem->vaddr);
 			return 0;
@@ -346,45 +360,30 @@ static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 
 	return ret;
 }
+EXPORT_SYMBOL(drm_gem_shmem_vmap);
 
 /*
- * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
+ * drm_gem_shmem_vunmap - Unmap a virtual mapping for a shmem GEM object
  * @shmem: shmem GEM object
- * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
- *       store.
- *
- * This function makes sure that a contiguous kernel virtual address mapping
- * exists for the buffer backing the shmem GEM object. It hides the differences
- * between dma-buf imported and natively allocated objects.
+ * @map: Kernel virtual address where the SHMEM GEM object was mapped
  *
- * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
+ * This function cleans up a kernel virtual address mapping acquired by
+ * drm_gem_shmem_vmap(). The mapping is only removed when the use count drops to
+ * zero.
  *
- * Returns:
- * 0 on success or a negative error code on failure.
+ * This function hides the differences between dma-buf imported and natively
+ * allocated objects.
  */
-int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
-		       struct iosys_map *map)
-{
-	int ret;
-
-	ret = mutex_lock_interruptible(&shmem->vmap_lock);
-	if (ret)
-		return ret;
-	ret = drm_gem_shmem_vmap_locked(shmem, map);
-	mutex_unlock(&shmem->vmap_lock);
-
-	return ret;
-}
-EXPORT_SYMBOL(drm_gem_shmem_vmap);
-
-static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
-					struct iosys_map *map)
+void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
+			  struct iosys_map *map)
 {
 	struct drm_gem_object *obj = &shmem->base;
 
 	if (obj->import_attach) {
 		dma_buf_vunmap(obj->import_attach->dmabuf, map);
 	} else {
+		dma_resv_assert_held(shmem->base.resv);
+
 		if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
 			return;
 
@@ -397,26 +396,6 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
 
 	shmem->vaddr = NULL;
 }
-
-/*
- * drm_gem_shmem_vunmap - Unmap a virtual mapping for a shmem GEM object
- * @shmem: shmem GEM object
- * @map: Kernel virtual address where the SHMEM GEM object was mapped
- *
- * This function cleans up a kernel virtual address mapping acquired by
- * drm_gem_shmem_vmap(). The mapping is only removed when the use count drops to
- * zero.
- *
- * This function hides the differences between dma-buf imported and natively
- * allocated objects.
- */
-void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
-			  struct iosys_map *map)
-{
-	mutex_lock(&shmem->vmap_lock);
-	drm_gem_shmem_vunmap_locked(shmem, map);
-	mutex_unlock(&shmem->vmap_lock);
-}
 EXPORT_SYMBOL(drm_gem_shmem_vunmap);
 
 static int
@@ -447,24 +426,24 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
  */
 int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv)
 {
-	mutex_lock(&shmem->pages_lock);
+	dma_resv_assert_held(shmem->base.resv);
 
 	if (shmem->madv >= 0)
 		shmem->madv = madv;
 
 	madv = shmem->madv;
 
-	mutex_unlock(&shmem->pages_lock);
-
 	return (madv >= 0);
 }
 EXPORT_SYMBOL(drm_gem_shmem_madvise);
 
-void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem)
+void drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem)
 {
 	struct drm_gem_object *obj = &shmem->base;
 	struct drm_device *dev = obj->dev;
 
+	dma_resv_assert_held(shmem->base.resv);
+
 	drm_WARN_ON(obj->dev, !drm_gem_shmem_is_purgeable(shmem));
 
 	dma_unmap_sgtable(dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
@@ -472,7 +451,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem)
 	kfree(shmem->sgt);
 	shmem->sgt = NULL;
 
-	drm_gem_shmem_put_pages_locked(shmem);
+	drm_gem_shmem_put_pages(shmem);
 
 	shmem->madv = -1;
 
@@ -488,17 +467,6 @@ void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem)
 
 	invalidate_mapping_pages(file_inode(obj->filp)->i_mapping, 0, (loff_t)-1);
 }
-EXPORT_SYMBOL(drm_gem_shmem_purge_locked);
-
-bool drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem)
-{
-	if (!mutex_trylock(&shmem->pages_lock))
-		return false;
-	drm_gem_shmem_purge_locked(shmem);
-	mutex_unlock(&shmem->pages_lock);
-
-	return true;
-}
 EXPORT_SYMBOL(drm_gem_shmem_purge);
 
 /**
@@ -551,7 +519,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 	/* We don't use vmf->pgoff since that has the fake offset */
 	page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
 
-	mutex_lock(&shmem->pages_lock);
+	dma_resv_lock(shmem->base.resv, NULL);
 
 	if (page_offset >= num_pages ||
 	    drm_WARN_ON_ONCE(obj->dev, !shmem->pages) ||
@@ -563,7 +531,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
 	}
 
-	mutex_unlock(&shmem->pages_lock);
+	dma_resv_unlock(shmem->base.resv);
 
 	return ret;
 }
@@ -575,7 +543,7 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
-	mutex_lock(&shmem->pages_lock);
+	dma_resv_lock(shmem->base.resv, NULL);
 
 	/*
 	 * We should have already pinned the pages when the buffer was first
@@ -585,7 +553,7 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
 	if (!drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
 		shmem->pages_use_count++;
 
-	mutex_unlock(&shmem->pages_lock);
+	dma_resv_unlock(shmem->base.resv);
 
 	drm_gem_vm_open(vma);
 }
@@ -595,7 +563,10 @@ static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
 	struct drm_gem_object *obj = vma->vm_private_data;
 	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
 
+	dma_resv_lock(shmem->base.resv, NULL);
 	drm_gem_shmem_put_pages(shmem);
+	dma_resv_unlock(shmem->base.resv);
+
 	drm_gem_vm_close(vma);
 }
 
@@ -633,7 +604,10 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
 		return ret;
 	}
 
+	dma_resv_lock(shmem->base.resv, NULL);
 	ret = drm_gem_shmem_get_pages(shmem);
+	dma_resv_unlock(shmem->base.resv);
+
 	if (ret)
 		return ret;
 
@@ -699,7 +673,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_
 
 	drm_WARN_ON(obj->dev, obj->import_attach);
 
-	ret = drm_gem_shmem_get_pages_locked(shmem);
+	ret = drm_gem_shmem_get_pages(shmem);
 	if (ret)
 		return ERR_PTR(ret);
 
@@ -721,7 +695,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_
 	sg_free_table(sgt);
 	kfree(sgt);
 err_put_pages:
-	drm_gem_shmem_put_pages_locked(shmem);
+	drm_gem_shmem_put_pages(shmem);
 	return ERR_PTR(ret);
 }
 
@@ -746,11 +720,11 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem)
 	int ret;
 	struct sg_table *sgt;
 
-	ret = mutex_lock_interruptible(&shmem->pages_lock);
+	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
 	if (ret)
 		return ERR_PTR(ret);
 	sgt = drm_gem_shmem_get_pages_sgt_locked(shmem);
-	mutex_unlock(&shmem->pages_lock);
+	dma_resv_unlock(shmem->base.resv);
 
 	return sgt;
 }
diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
index 10252dc11a22..4f9736e5f929 100644
--- a/drivers/gpu/drm/lima/lima_gem.c
+++ b/drivers/gpu/drm/lima/lima_gem.c
@@ -34,7 +34,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 
 	new_size = min(new_size, bo->base.base.size);
 
-	mutex_lock(&bo->base.pages_lock);
+	dma_resv_lock(bo->base.base.resv, NULL);
 
 	if (bo->base.pages) {
 		pages = bo->base.pages;
@@ -42,7 +42,7 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 		pages = kvmalloc_array(bo->base.base.size >> PAGE_SHIFT,
 				       sizeof(*pages), GFP_KERNEL | __GFP_ZERO);
 		if (!pages) {
-			mutex_unlock(&bo->base.pages_lock);
+			dma_resv_unlock(bo->base.base.resv);
 			return -ENOMEM;
 		}
 
@@ -56,13 +56,13 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm)
 		struct page *page = shmem_read_mapping_page(mapping, i);
 
 		if (IS_ERR(page)) {
-			mutex_unlock(&bo->base.pages_lock);
+			dma_resv_unlock(bo->base.base.resv);
 			return PTR_ERR(page);
 		}
 		pages[i] = page;
 	}
 
-	mutex_unlock(&bo->base.pages_lock);
+	dma_resv_unlock(bo->base.base.resv);
 
 	ret = sg_alloc_table_from_pages(&sgt, pages, i, 0,
 					new_size, GFP_KERNEL);
diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index bbada731bbbd..d9dda6acdfac 100644
--- a/drivers/gpu/drm/panfrost/panfrost_drv.c
+++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
@@ -407,6 +407,10 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
 
 	bo = to_panfrost_bo(gem_obj);
 
+	ret = dma_resv_lock_interruptible(bo->base.base.resv, NULL);
+	if (ret)
+		goto out_put_object;
+
 	mutex_lock(&pfdev->shrinker_lock);
 	mutex_lock(&bo->mappings.lock);
 	if (args->madv == PANFROST_MADV_DONTNEED) {
@@ -444,7 +448,8 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
 out_unlock_mappings:
 	mutex_unlock(&bo->mappings.lock);
 	mutex_unlock(&pfdev->shrinker_lock);
-
+	dma_resv_unlock(bo->base.base.resv);
+out_put_object:
 	drm_gem_object_put(gem_obj);
 	return ret;
 }
diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
index bf0170782f25..6a71a2555f85 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
@@ -48,14 +48,14 @@ static bool panfrost_gem_purge(struct drm_gem_object *obj)
 	if (!mutex_trylock(&bo->mappings.lock))
 		return false;
 
-	if (!mutex_trylock(&shmem->pages_lock))
+	if (!dma_resv_trylock(shmem->base.resv))
 		goto unlock_mappings;
 
 	panfrost_gem_teardown_mappings_locked(bo);
-	drm_gem_shmem_purge_locked(&bo->base);
+	drm_gem_shmem_purge(&bo->base);
 	ret = true;
 
-	mutex_unlock(&shmem->pages_lock);
+	dma_resv_unlock(shmem->base.resv);
 
 unlock_mappings:
 	mutex_unlock(&bo->mappings.lock);
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index 666a5e53fe19..0679df57f394 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -443,6 +443,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	struct panfrost_gem_mapping *bomapping;
 	struct panfrost_gem_object *bo;
 	struct address_space *mapping;
+	struct drm_gem_object *obj;
 	pgoff_t page_offset;
 	struct sg_table *sgt;
 	struct page **pages;
@@ -465,15 +466,16 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	page_offset = addr >> PAGE_SHIFT;
 	page_offset -= bomapping->mmnode.start;
 
-	mutex_lock(&bo->base.pages_lock);
+	obj = &bo->base.base;
+
+	dma_resv_lock(obj->resv, NULL);
 
 	if (!bo->base.pages) {
 		bo->sgts = kvmalloc_array(bo->base.base.size / SZ_2M,
 				     sizeof(struct sg_table), GFP_KERNEL | __GFP_ZERO);
 		if (!bo->sgts) {
-			mutex_unlock(&bo->base.pages_lock);
 			ret = -ENOMEM;
-			goto err_bo;
+			goto err_unlock;
 		}
 
 		pages = kvmalloc_array(bo->base.base.size >> PAGE_SHIFT,
@@ -481,9 +483,8 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 		if (!pages) {
 			kvfree(bo->sgts);
 			bo->sgts = NULL;
-			mutex_unlock(&bo->base.pages_lock);
 			ret = -ENOMEM;
-			goto err_bo;
+			goto err_unlock;
 		}
 		bo->base.pages = pages;
 		bo->base.pages_use_count = 1;
@@ -491,7 +492,6 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 		pages = bo->base.pages;
 		if (pages[page_offset]) {
 			/* Pages are already mapped, bail out. */
-			mutex_unlock(&bo->base.pages_lock);
 			goto out;
 		}
 	}
@@ -502,14 +502,11 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	for (i = page_offset; i < page_offset + NUM_FAULT_PAGES; i++) {
 		pages[i] = shmem_read_mapping_page(mapping, i);
 		if (IS_ERR(pages[i])) {
-			mutex_unlock(&bo->base.pages_lock);
 			ret = PTR_ERR(pages[i]);
 			goto err_pages;
 		}
 	}
 
-	mutex_unlock(&bo->base.pages_lock);
-
 	sgt = &bo->sgts[page_offset / (SZ_2M / PAGE_SIZE)];
 	ret = sg_alloc_table_from_pages(sgt, pages + page_offset,
 					NUM_FAULT_PAGES, 0, SZ_2M, GFP_KERNEL);
@@ -528,6 +525,8 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	dev_dbg(pfdev->dev, "mapped page fault @ AS%d %llx", as, addr);
 
 out:
+	dma_resv_unlock(obj->resv);
+
 	panfrost_gem_mapping_put(bomapping);
 
 	return 0;
@@ -536,6 +535,8 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	sg_free_table(sgt);
 err_pages:
 	drm_gem_shmem_put_pages(&bo->base);
+err_unlock:
+	dma_resv_unlock(obj->resv);
 err_bo:
 	panfrost_gem_mapping_put(bomapping);
 	return ret;
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index 5994fed5e327..20ddcd799df9 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -26,11 +26,6 @@ struct drm_gem_shmem_object {
 	 */
 	struct drm_gem_object base;
 
-	/**
-	 * @pages_lock: Protects the page table and use count
-	 */
-	struct mutex pages_lock;
-
 	/**
 	 * @pages: Page table
 	 */
@@ -65,11 +60,6 @@ struct drm_gem_shmem_object {
 	 */
 	struct sg_table *sgt;
 
-	/**
-	 * @vmap_lock: Protects the vmap address and use count
-	 */
-	struct mutex vmap_lock;
-
 	/**
 	 * @vaddr: Kernel virtual address of the backing memory
 	 */
@@ -109,7 +99,6 @@ struct drm_gem_shmem_object {
 struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size);
 void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem);
 
-int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem);
 void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem);
 int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem);
 void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem);
@@ -128,8 +117,7 @@ static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem
 		!shmem->base.dma_buf && !shmem->base.import_attach;
 }
 
-void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem);
-bool drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem);
+void drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem);
 
 struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem);
 struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem);
-- 
2.40.1

Re: [PATCH v4 6/6] drm/shmem-helper: Switch to reservation lock

[Boris Brezillon]

Hi Dmitry,

On Tue, 30 May 2023 01:39:35 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:

> Replace all drm-shmem locks with a GEM reservation lock. This makes locks
> consistent with dma-buf locking convention where importers are responsible
> for holding reservation lock for all operations performed over dma-bufs,
> preventing deadlock between dma-buf importers and exporters.

I've rebased some of my work on drm-misc-next this morning and noticed
that the drm_gem_shmem_get_pages() I was using to pin pages no longer
exists, so I ended looking at this patch to check what I should use
instead, and I have a few questions/comments.

> 
> Suggested-by: Daniel Vetter <daniel@ffwll.ch>
> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c        | 210 ++++++++----------
>  drivers/gpu/drm/lima/lima_gem.c               |   8 +-
>  drivers/gpu/drm/panfrost/panfrost_drv.c       |   7 +-
>  .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   6 +-
>  drivers/gpu/drm/panfrost/panfrost_mmu.c       |  19 +-
>  include/drm/drm_gem_shmem_helper.h            |  14 +-
>  6 files changed, 116 insertions(+), 148 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 4ea6507a77e5..a783d2245599 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -88,8 +88,6 @@ __drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
>  	if (ret)
>  		goto err_release;
>  
> -	mutex_init(&shmem->pages_lock);
> -	mutex_init(&shmem->vmap_lock);
>  	INIT_LIST_HEAD(&shmem->madv_list);
>  
>  	if (!private) {
> @@ -141,11 +139,13 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  {
>  	struct drm_gem_object *obj = &shmem->base;
>  
> -	drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> -
>  	if (obj->import_attach) {
>  		drm_prime_gem_destroy(obj, shmem->sgt);
>  	} else {
> +		dma_resv_lock(shmem->base.resv, NULL);
> +
> +		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> +
>  		if (shmem->sgt) {
>  			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
>  					  DMA_BIDIRECTIONAL, 0);
> @@ -154,22 +154,24 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  		}
>  		if (shmem->pages)
>  			drm_gem_shmem_put_pages(shmem);
> -	}
>  
> -	drm_WARN_ON(obj->dev, shmem->pages_use_count);
> +		drm_WARN_ON(obj->dev, shmem->pages_use_count);
> +
> +		dma_resv_unlock(shmem->base.resv);
> +	}
>  
>  	drm_gem_object_release(obj);
> -	mutex_destroy(&shmem->pages_lock);
> -	mutex_destroy(&shmem->vmap_lock);
>  	kfree(shmem);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_free);
>  
> -static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
> +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)

I find this name change confusing, because the function requires the
GEM resv lock to be held, and the _locked suffix was making it pretty
clear.

>  {
>  	struct drm_gem_object *obj = &shmem->base;
>  	struct page **pages;
>  
> +	dma_resv_assert_held(shmem->base.resv);
> +
>  	if (shmem->pages_use_count++ > 0)
>  		return 0;
>  
> @@ -197,35 +199,16 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
>  }
>  
>  /*
> - * drm_gem_shmem_get_pages - Allocate backing pages for a shmem GEM object
> + * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
>   * @shmem: shmem GEM object
>   *
> - * This function makes sure that backing pages exists for the shmem GEM object
> - * and increases the use count.
> - *
> - * Returns:
> - * 0 on success or a negative error code on failure.
> + * This function decreases the use count and puts the backing pages when use drops to zero.
>   */
> -int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> +void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)

Same comment about the name change. That's even more confusing since
this function was previously taking care of the locking. Also not sure
why you'd want to expose this _put() helper when the _get() helper is
private.

>  {
>  	struct drm_gem_object *obj = &shmem->base;
> -	int ret;
>  
> -	drm_WARN_ON(obj->dev, obj->import_attach);
> -
> -	ret = mutex_lock_interruptible(&shmem->pages_lock);
> -	if (ret)
> -		return ret;
> -	ret = drm_gem_shmem_get_pages_locked(shmem);
> -	mutex_unlock(&shmem->pages_lock);
> -
> -	return ret;
> -}
> -EXPORT_SYMBOL(drm_gem_shmem_get_pages);
> -
> -static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
> -{
> -	struct drm_gem_object *obj = &shmem->base;
> +	dma_resv_assert_held(shmem->base.resv);
>  
>  	if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
>  		return;
> @@ -243,20 +226,25 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>  			  shmem->pages_mark_accessed_on_put);
>  	shmem->pages = NULL;
>  }
> +EXPORT_SYMBOL(drm_gem_shmem_put_pages);
>  
> -/*
> - * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
> - * @shmem: shmem GEM object
> - *
> - * This function decreases the use count and puts the backing pages when use drops to zero.
> - */
> -void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
> +static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
>  {
> -	mutex_lock(&shmem->pages_lock);
> -	drm_gem_shmem_put_pages_locked(shmem);
> -	mutex_unlock(&shmem->pages_lock);
> +	int ret;
> +
> +	dma_resv_assert_held(shmem->base.resv);
> +
> +	ret = drm_gem_shmem_get_pages(shmem);
> +
> +	return ret;
> +}
> +
> +static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
> +{
> +	dma_resv_assert_held(shmem->base.resv);
> +
> +	drm_gem_shmem_put_pages(shmem);
>  }
> -EXPORT_SYMBOL(drm_gem_shmem_put_pages);
>  
>  /**
>   * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
> @@ -271,10 +259,17 @@ EXPORT_SYMBOL(drm_gem_shmem_put_pages);
>  int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
>  {
>  	struct drm_gem_object *obj = &shmem->base;
> +	int ret;
>  
>  	drm_WARN_ON(obj->dev, obj->import_attach);
>  
> -	return drm_gem_shmem_get_pages(shmem);
> +	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
> +	if (ret)
> +		return ret;

I think here is the major problem I have with this patch: you've made
drm_gem_shmem_{get_pages,pin}() private, which forces me to call
drm_gem_shmem_pin() in a path where I already acquired the resv lock
(using the drm_exec infra proposed by Christian). That would
probably work if you were letting ret == -EALREADY go through, but I'm
wondering if it wouldn't be preferable to expose
drm_gem_shmem_pin_locked().

> +	ret = drm_gem_shmem_pin_locked(shmem);
> +	dma_resv_unlock(shmem->base.resv);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_gem_shmem_pin);
>  
> @@ -291,12 +286,29 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
>  
>  	drm_WARN_ON(obj->dev, obj->import_attach);
>  
> -	drm_gem_shmem_put_pages(shmem);
> +	dma_resv_lock(shmem->base.resv, NULL);
> +	drm_gem_shmem_unpin_locked(shmem);
> +	dma_resv_unlock(shmem->base.resv);
>  }
>  EXPORT_SYMBOL(drm_gem_shmem_unpin);

If we want to be consistent, let's just expose drm_gem_shmem_unpin()
and drm_gem_shmem_pin() and keep drm_gem_shmem_{get,put}_pages()
private, or even better, rename them drm_gem_shmem_{pin,unpin}_locked()
insert of having drm_gem_shmem_{pin,unpin}_locked() wrappers that just
forward the call to drm_gem_shmem_{get,put}_pages().

>  
> -static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
> -				     struct iosys_map *map)
> +/*
> + * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
> + * @shmem: shmem GEM object
> + * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
> + *       store.
> + *
> + * This function makes sure that a contiguous kernel virtual address mapping
> + * exists for the buffer backing the shmem GEM object. It hides the differences
> + * between dma-buf imported and natively allocated objects.
> + *
> + * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
> +		       struct iosys_map *map)

Same problem with this renaming: it's confusing because this function
was previously taking care of the locking, and it's no longer the case.
That's actually true for other public functions your patching, but I
won't go over all of them.

I know this patch has been under discussion for quite some time, and has
been validated by other devs/maintainers, but I'd like to understand the
reasoning behind these decisions. Not the decision to replace all locks
by dma_resv, which I kinda understand, but the decision to change the
behavior of functions without making the name reflect the new behavior
(_locked prefix), or the fact we now prohibit some functions to
succeed when the dma_resv lock is taken by the driver beforehand (which,
unless I'm mistaken, will happen in the VM_BIND logic, and can happen
in the SUBMIT ioctl too depending on the driver).

Regards,

Boris

Re: [PATCH v4 6/6] drm/shmem-helper: Switch to reservation lock

[Boris Brezillon]

On Mon, 26 Jun 2023 11:40:14 +0200
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> Hi Dmitry,
> 
> On Tue, 30 May 2023 01:39:35 +0300
> Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:
> 
> > Replace all drm-shmem locks with a GEM reservation lock. This makes locks
> > consistent with dma-buf locking convention where importers are responsible
> > for holding reservation lock for all operations performed over dma-bufs,
> > preventing deadlock between dma-buf importers and exporters.  
> 
> I've rebased some of my work on drm-misc-next this morning and noticed
> that the drm_gem_shmem_get_pages() I was using to pin pages no longer
> exists, so I ended looking at this patch to check what I should use
> instead, and I have a few questions/comments.
> 
> > 
> > Suggested-by: Daniel Vetter <daniel@ffwll.ch>
> > Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
> > Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
> > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> > ---
> >  drivers/gpu/drm/drm_gem_shmem_helper.c        | 210 ++++++++----------
> >  drivers/gpu/drm/lima/lima_gem.c               |   8 +-
> >  drivers/gpu/drm/panfrost/panfrost_drv.c       |   7 +-
> >  .../gpu/drm/panfrost/panfrost_gem_shrinker.c  |   6 +-
> >  drivers/gpu/drm/panfrost/panfrost_mmu.c       |  19 +-
> >  include/drm/drm_gem_shmem_helper.h            |  14 +-
> >  6 files changed, 116 insertions(+), 148 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index 4ea6507a77e5..a783d2245599 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -88,8 +88,6 @@ __drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
> >  	if (ret)
> >  		goto err_release;
> >  
> > -	mutex_init(&shmem->pages_lock);
> > -	mutex_init(&shmem->vmap_lock);
> >  	INIT_LIST_HEAD(&shmem->madv_list);
> >  
> >  	if (!private) {
> > @@ -141,11 +139,13 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> >  {
> >  	struct drm_gem_object *obj = &shmem->base;
> >  
> > -	drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> > -
> >  	if (obj->import_attach) {
> >  		drm_prime_gem_destroy(obj, shmem->sgt);
> >  	} else {
> > +		dma_resv_lock(shmem->base.resv, NULL);
> > +
> > +		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
> > +
> >  		if (shmem->sgt) {
> >  			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
> >  					  DMA_BIDIRECTIONAL, 0);
> > @@ -154,22 +154,24 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> >  		}
> >  		if (shmem->pages)
> >  			drm_gem_shmem_put_pages(shmem);
> > -	}
> >  
> > -	drm_WARN_ON(obj->dev, shmem->pages_use_count);
> > +		drm_WARN_ON(obj->dev, shmem->pages_use_count);
> > +
> > +		dma_resv_unlock(shmem->base.resv);
> > +	}
> >  
> >  	drm_gem_object_release(obj);
> > -	mutex_destroy(&shmem->pages_lock);
> > -	mutex_destroy(&shmem->vmap_lock);
> >  	kfree(shmem);
> >  }
> >  EXPORT_SYMBOL_GPL(drm_gem_shmem_free);
> >  
> > -static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
> > +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)  
> 
> I find this name change confusing, because the function requires the
> GEM resv lock to be held, and the _locked suffix was making it pretty
> clear.
> 
> >  {
> >  	struct drm_gem_object *obj = &shmem->base;
> >  	struct page **pages;
> >  
> > +	dma_resv_assert_held(shmem->base.resv);
> > +
> >  	if (shmem->pages_use_count++ > 0)
> >  		return 0;
> >  
> > @@ -197,35 +199,16 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
> >  }
> >  
> >  /*
> > - * drm_gem_shmem_get_pages - Allocate backing pages for a shmem GEM object
> > + * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
> >   * @shmem: shmem GEM object
> >   *
> > - * This function makes sure that backing pages exists for the shmem GEM object
> > - * and increases the use count.
> > - *
> > - * Returns:
> > - * 0 on success or a negative error code on failure.
> > + * This function decreases the use count and puts the backing pages when use drops to zero.
> >   */
> > -int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> > +void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)  
> 
> Same comment about the name change. That's even more confusing since
> this function was previously taking care of the locking. Also not sure
> why you'd want to expose this _put() helper when the _get() helper is
> private.
> 
> >  {
> >  	struct drm_gem_object *obj = &shmem->base;
> > -	int ret;
> >  
> > -	drm_WARN_ON(obj->dev, obj->import_attach);
> > -
> > -	ret = mutex_lock_interruptible(&shmem->pages_lock);
> > -	if (ret)
> > -		return ret;
> > -	ret = drm_gem_shmem_get_pages_locked(shmem);
> > -	mutex_unlock(&shmem->pages_lock);
> > -
> > -	return ret;
> > -}
> > -EXPORT_SYMBOL(drm_gem_shmem_get_pages);
> > -
> > -static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
> > -{
> > -	struct drm_gem_object *obj = &shmem->base;
> > +	dma_resv_assert_held(shmem->base.resv);
> >  
> >  	if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count))
> >  		return;
> > @@ -243,20 +226,25 @@ static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
> >  			  shmem->pages_mark_accessed_on_put);
> >  	shmem->pages = NULL;
> >  }
> > +EXPORT_SYMBOL(drm_gem_shmem_put_pages);
> >  
> > -/*
> > - * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
> > - * @shmem: shmem GEM object
> > - *
> > - * This function decreases the use count and puts the backing pages when use drops to zero.
> > - */
> > -void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
> > +static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
> >  {
> > -	mutex_lock(&shmem->pages_lock);
> > -	drm_gem_shmem_put_pages_locked(shmem);
> > -	mutex_unlock(&shmem->pages_lock);
> > +	int ret;
> > +
> > +	dma_resv_assert_held(shmem->base.resv);
> > +
> > +	ret = drm_gem_shmem_get_pages(shmem);
> > +
> > +	return ret;
> > +}
> > +
> > +static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
> > +{
> > +	dma_resv_assert_held(shmem->base.resv);
> > +
> > +	drm_gem_shmem_put_pages(shmem);
> >  }
> > -EXPORT_SYMBOL(drm_gem_shmem_put_pages);
> >  
> >  /**
> >   * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
> > @@ -271,10 +259,17 @@ EXPORT_SYMBOL(drm_gem_shmem_put_pages);
> >  int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
> >  {
> >  	struct drm_gem_object *obj = &shmem->base;
> > +	int ret;
> >  
> >  	drm_WARN_ON(obj->dev, obj->import_attach);
> >  
> > -	return drm_gem_shmem_get_pages(shmem);
> > +	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
> > +	if (ret)
> > +		return ret;  
> 
> I think here is the major problem I have with this patch: you've made
> drm_gem_shmem_{get_pages,pin}() private, which forces me to call
> drm_gem_shmem_pin() in a path where I already acquired the resv lock
> (using the drm_exec infra proposed by Christian). That would
> probably work if you were letting ret == -EALREADY go through, but I'm
> wondering if it wouldn't be preferable to expose
> drm_gem_shmem_pin_locked().
> 
> > +	ret = drm_gem_shmem_pin_locked(shmem);
> > +	dma_resv_unlock(shmem->base.resv);
> > +
> > +	return ret;
> >  }
> >  EXPORT_SYMBOL(drm_gem_shmem_pin);
> >  
> > @@ -291,12 +286,29 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
> >  
> >  	drm_WARN_ON(obj->dev, obj->import_attach);
> >  
> > -	drm_gem_shmem_put_pages(shmem);
> > +	dma_resv_lock(shmem->base.resv, NULL);
> > +	drm_gem_shmem_unpin_locked(shmem);
> > +	dma_resv_unlock(shmem->base.resv);
> >  }
> >  EXPORT_SYMBOL(drm_gem_shmem_unpin);  
> 
> If we want to be consistent, let's just expose drm_gem_shmem_unpin()
> and drm_gem_shmem_pin() and keep drm_gem_shmem_{get,put}_pages()
> private, or even better, rename them drm_gem_shmem_{pin,unpin}_locked()
> insert of having drm_gem_shmem_{pin,unpin}_locked() wrappers that just
> forward the call to drm_gem_shmem_{get,put}_pages().
> 
> >  
> > -static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
> > -				     struct iosys_map *map)
> > +/*
> > + * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
> > + * @shmem: shmem GEM object
> > + * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
> > + *       store.
> > + *
> > + * This function makes sure that a contiguous kernel virtual address mapping
> > + * exists for the buffer backing the shmem GEM object. It hides the differences
> > + * between dma-buf imported and natively allocated objects.
> > + *
> > + * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
> > + *
> > + * Returns:
> > + * 0 on success or a negative error code on failure.
> > + */
> > +int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
> > +		       struct iosys_map *map)  
> 
> Same problem with this renaming: it's confusing because this function
> was previously taking care of the locking, and it's no longer the case.
> That's actually true for other public functions your patching, but I
> won't go over all of them.

vmap() is less of a problem, because we're not supposed to call
drm_gem_shmem_vmap() directly, but rather go through drm_gem_vmap().
This should probably be clarified in the doc though, with this sort of
disclaimer: "don't use this function to map stuff, only use it to
implement drm_gem_object_funcs::vmap()."

Also noticed that the drm_gem API has the _locked pattern reversed,
with a few drm_gem_xxx_unlocked() helper that take the lock and call
the drm_gem_xxx() function. Don't have a strong opinion on whether this
is better than the xxx_locked() and xxx() pattern or not, but the fact
things are inconsistent across the API (drm_gem_pin() is letting the
backend take the lock before pinning pages, when drm_gem_vmap() is
not) is super confusing.

Re: [PATCH v4 6/6] drm/shmem-helper: Switch to reservation lock

[Dmitry Osipenko]

On 6/26/23 12:40, Boris Brezillon wrote:
> Same problem with this renaming: it's confusing because this function
> was previously taking care of the locking, and it's no longer the case.
> That's actually true for other public functions your patching, but I
> won't go over all of them.
> 
> I know this patch has been under discussion for quite some time, and has
> been validated by other devs/maintainers, but I'd like to understand the
> reasoning behind these decisions. Not the decision to replace all locks
> by dma_resv, which I kinda understand, but the decision to change the
> behavior of functions without making the name reflect the new behavior
> (_locked prefix), or the fact we now prohibit some functions to
> succeed when the dma_resv lock is taken by the driver beforehand (which,
> unless I'm mistaken, will happen in the VM_BIND logic, and can happen
> in the SUBMIT ioctl too depending on the driver).

Adding explicit _locked/unlocked postfix to all function names indeed
won't hurt to do. There was no decision made about the function names,
the old functions kept the old name where possible to minimize code
changes during transition to the resv lock. Improving the names could be
the next step.

Thanks for the feedback!

-- 
Best regards,
Dmitry

Re: [PATCH v4 6/6] drm/shmem-helper: Switch to reservation lock

[Dmitry Osipenko]

On 6/26/23 12:40, Boris Brezillon wrote:
> I think here is the major problem I have with this patch: you've made
> drm_gem_shmem_{get_pages,pin}() private, which forces me to call
> drm_gem_shmem_pin() in a path where I already acquired the resv lock
> (using the drm_exec infra proposed by Christian). That would
> probably work if you were letting ret == -EALREADY go through, but I'm
> wondering if it wouldn't be preferable to expose
> drm_gem_shmem_pin_locked().

You should be free to expose the necessary functions. They are private
because nobody need them so far and we don't want to export unused
functions.

-- 
Best regards,
Dmitry

Re: [PATCH v4 0/6] Move dma-buf mmap() reservation locking down to exporters

[Dmitry Osipenko]

On 5/30/23 01:39, Dmitry Osipenko wrote:
> This patchset makes dma-buf exporters responisble for taking care of
> the reservation lock. I also included patch that moves drm-shmem to use
> reservation lock, to let CI test the whole set. I'm going to take all
> the patches via the drm-misc tree, please give an ack.
> 
> Previous policy stated that dma-buf core takes the lock around mmap()
> callback. Which meant that both importers and exporters shouldn't touch
> the reservation lock in the mmap() code path. This worked well until
> Intel-CI found a deadlock problem in a case of self-imported dma-buf [1].
> 
> The problem happens when userpace mmaps a self-imported dma-buf, i.e.
> mmaps the dma-buf FD. DRM core treats self-imported dma-bufs as own GEMs
> [2]. There is no way to differentiate a prime GEM from a normal GEM for
> drm-shmem in drm_gem_shmem_mmap(), which resulted in a deadlock problem
> for drm-shmem mmap() code path once it's switched to use reservation lock.
> 
> It was difficult to fix the drm-shmem problem without adjusting dma-buf
> locking policy. In parctice not much changed from importers perspective
> because previosly dma-buf was taking the lock in between of importers
> and exporters. Now this lock is shifted down to exporters.
> 
> [1] https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_114671v2/shard-snb5/igt@prime_vgem@sync@rcs0.html
> [2] https://elixir.bootlin.com/linux/v6.3-rc4/source/drivers/gpu/drm/drm_prime.c#L924

Applied to misc-next

-- 
Best regards,
Dmitry