[PATCH v2 04/23] drm/msm: Decouple vma tracking from obj lock

Rob Clark
2023-03-20T14:44:45Z

We need to use the inuse count to track that a BO is pinned until
we have the hw_fence. But we want to remove the obj lock from the
job_run() path as this could deadlock against reclaim/shrinker
(because it is blocking the hw_fence from eventually being signaled).
So split that tracking out into a per-vma lock with narrower scope.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
drivers/gpu/drm/msm/msm_gem.h | 1 +
drivers/gpu/drm/msm/msm_gem_vma.c | 44 ++++++++++++++++++++++++----
drivers/gpu/drm/msm/msm_ringbuffer.c | 2 +-
3 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index d3219c523034..1929f09c5b0d 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -59,6 +59,7 @@ struct msm_fence_context;

struct msm_gem_vma {
struct drm_mm_node node;
+ spinlock_t lock;
uint64_t iova;
struct msm_gem_address_space *aspace;
struct list_head list; /* node in msm_gem_object::vmas */
diff --git a/drivers/gpu/drm/msm/msm_gem_vma.c b/drivers/gpu/drm/msm/msm_gem_vma.c
index 2827679dc39a..98287ed99960 100644
--- a/drivers/gpu/drm/msm/msm_gem_vma.c
+++ b/drivers/gpu/drm/msm/msm_gem_vma.c
@@ -40,19 +40,28 @@ msm_gem_address_space_get(struct msm_gem_address_space *aspace)

bool msm_gem_vma_inuse(struct msm_gem_vma *vma)
{
+ bool ret = true;
+
+ spin_lock(&vma->lock);
+
if (vma->inuse > 0)
- return true;
+ goto out;

while (vma->fence_mask) {
unsigned idx = ffs(vma->fence_mask) - 1;

if (!msm_fence_completed(vma->fctx[idx], vma->fence[idx]))
- return true;
+ goto out;

vma->fence_mask &= ~BIT(idx);
}

- return false;
+ ret = false;
+
+out:
+ spin_unlock(&vma->lock);
+
+ return ret;
}

/* Actually unmap memory for the vma */
@@ -73,8 +82,7 @@ void msm_gem_vma_purge(struct msm_gem_vma *vma)
vma->mapped = false;
}

-/* Remove reference counts for the mapping */
-void msm_gem_vma_unpin(struct msm_gem_vma *vma)
+static void vma_unpin_locked(struct msm_gem_vma *vma)
{
if (GEM_WARN_ON(!vma->inuse))
return;
@@ -82,13 +90,23 @@ void msm_gem_vma_unpin(struct msm_gem_vma *vma)
vma->inuse--;
}

+/* Remove reference counts for the mapping */
+void msm_gem_vma_unpin(struct msm_gem_vma *vma)
+{
+ spin_lock(&vma->lock);
+ vma_unpin_locked(vma);
+ spin_unlock(&vma->lock);
+}
+
/* Replace pin reference with fence: */
void msm_gem_vma_unpin_fenced(struct msm_gem_vma *vma, struct msm_fence_context *fctx)
{
+ spin_lock(&vma->lock);
vma->fctx[fctx->index] = fctx;
vma->fence[fctx->index] = fctx->last_fence;
vma->fence_mask |= BIT(fctx->index);
- msm_gem_vma_unpin(vma);
+ vma_unpin_locked(vma);
+ spin_unlock(&vma->lock);
}

/* Map and pin vma: */
@@ -103,7 +121,9 @@ msm_gem_vma_map(struct msm_gem_vma *vma, int prot,
return -EINVAL;

/* Increase the usage counter */
+ spin_lock(&vma->lock);
vma->inuse++;
+ spin_unlock(&vma->lock);

if (vma->mapped)
return 0;
@@ -113,11 +133,22 @@ msm_gem_vma_map(struct msm_gem_vma *vma, int prot,
if (!aspace)
return 0;

+ /*
+ * NOTE: iommu/io-pgtable can allocate pages, so we cannot hold
+ * a lock across map/unmap which is also used in the job_run()
+ * path, as this can cause deadlock in job_run() vs shrinker/
+ * reclaim.
+ *
+ * Revisit this if we can come up with a scheme to pre-alloc pages
+ * for the pgtable in map/unmap ops.
+ */
ret = aspace->mmu->funcs->map(aspace->mmu, vma->iova, sgt, size, prot);

if (ret) {
vma->mapped = false;
+ spin_lock(&vma->lock);
vma->inuse--;
+ spin_unlock(&vma->lock);
}

return ret;
@@ -148,6 +179,7 @@ struct msm_gem_vma *msm_gem_vma_new(struct msm_gem_address_space *aspace)
if (!vma)
return NULL;

+ spin_lock_init(&vma->lock);
vma->aspace = aspace;

return vma;
diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
index 44a22b283730..31b4fbf96c36 100644
--- a/drivers/gpu/drm/msm/msm_ringbuffer.c
+++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
@@ -23,8 +23,8 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
for (i = 0; i < submit->nr_bos; i++) {
struct drm_gem_object *obj = &submit->bos[i].obj->base;

- msm_gem_lock(obj);
msm_gem_vma_unpin_fenced(submit->bos[i].vma, fctx);
+ msm_gem_lock(obj);
msm_gem_unpin_locked(obj);
msm_gem_unlock(obj);
submit->bos[i].flags &= ~(BO_VMA_PINNED | BO_OBJ_PINNED);
--
2.39.2