Re: [PATCH 05/26] drm/i915: Remove locking from i915_gem_object_prepare_read/write

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On 23/06/2020 15:28, Maarten Lankhorst wrote:
Execbuffer submission will perform its own WW locking, and we
cannot rely on the implicit lock there.

This also makes it clear that the GVT code will get a lockdep splat when
multiple batchbuffer shadows need to be performed in the same instance,
fix that up.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/gem/i915_gem_domain.c    | 20 ++++++-------------
  .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 13 ++++++++++--
  drivers/gpu/drm/i915/gem/i915_gem_object.h    |  1 -
  .../gpu/drm/i915/gem/selftests/huge_pages.c   |  5 ++++-
  .../i915/gem/selftests/i915_gem_coherency.c   | 14 +++++++++----
  .../drm/i915/gem/selftests/i915_gem_context.c | 12 ++++++++---
  drivers/gpu/drm/i915/gvt/cmd_parser.c         |  1 +
  drivers/gpu/drm/i915/i915_gem.c               | 20 +++++++++++++++++--
  8 files changed, 59 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
index c0acfc97fae3..8ebceebd11b0 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
@@ -576,19 +576,17 @@ int i915_gem_object_prepare_read(struct drm_i915_gem_object *obj,
  	if (!i915_gem_object_has_struct_page(obj))
  		return -ENODEV;
- ret = i915_gem_object_lock_interruptible(obj, NULL);
-	if (ret)
-		return ret;
+	assert_object_held(obj);
ret = i915_gem_object_wait(obj,
  				   I915_WAIT_INTERRUPTIBLE,
  				   MAX_SCHEDULE_TIMEOUT);
  	if (ret)
-		goto err_unlock;
+		return ret;
ret = i915_gem_object_pin_pages(obj);
  	if (ret)
-		goto err_unlock;
+		return ret;
if (obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ ||
  	    !static_cpu_has(X86_FEATURE_CLFLUSH)) {
@@ -616,8 +614,6 @@ int i915_gem_object_prepare_read(struct drm_i915_gem_object *obj,
err_unpin:
  	i915_gem_object_unpin_pages(obj);
-err_unlock:
-	i915_gem_object_unlock(obj);
  	return ret;
  }
@@ -630,20 +626,18 @@ int i915_gem_object_prepare_write(struct drm_i915_gem_object *obj,
  	if (!i915_gem_object_has_struct_page(obj))
  		return -ENODEV;
- ret = i915_gem_object_lock_interruptible(obj, NULL);
-	if (ret)
-		return ret;
+	assert_object_held(obj);
ret = i915_gem_object_wait(obj,
  				   I915_WAIT_INTERRUPTIBLE |
  				   I915_WAIT_ALL,
  				   MAX_SCHEDULE_TIMEOUT);
  	if (ret)
-		goto err_unlock;
+		return ret;
ret = i915_gem_object_pin_pages(obj);
  	if (ret)
-		goto err_unlock;
+		return ret;
if (obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE ||
  	    !static_cpu_has(X86_FEATURE_CLFLUSH)) {
@@ -680,7 +674,5 @@ int i915_gem_object_prepare_write(struct drm_i915_gem_object *obj,
err_unpin:
  	i915_gem_object_unpin_pages(obj);
-err_unlock:
-	i915_gem_object_unlock(obj);
  	return ret;
  }
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 391d22051b20..f896b1a4b38a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1003,11 +1003,14 @@ static void reloc_cache_reset(struct reloc_cache *cache)
vaddr = unmask_page(cache->vaddr);
  	if (cache->vaddr & KMAP) {
+		struct drm_i915_gem_object *obj =
+			(struct drm_i915_gem_object *)cache->node.mm;
  		if (cache->vaddr & CLFLUSH_AFTER)
  			mb();
kunmap_atomic(vaddr);
-		i915_gem_object_finish_access((struct drm_i915_gem_object *)cache->node.mm);
+		i915_gem_object_finish_access(obj);
+		i915_gem_object_unlock(obj);
  	} else {
  		struct i915_ggtt *ggtt = cache_to_ggtt(cache);
@@ -1042,10 +1045,16 @@ static void *reloc_kmap(struct drm_i915_gem_object *obj,
  		unsigned int flushes;
  		int err;
- err = i915_gem_object_prepare_write(obj, &flushes);
+		err = i915_gem_object_lock_interruptible(obj, NULL);
  		if (err)
  			return ERR_PTR(err);
+ err = i915_gem_object_prepare_write(obj, &flushes);
+		if (err) {
+			i915_gem_object_unlock(obj);
+			return ERR_PTR(err);
+		}
+
  		BUILD_BUG_ON(KMAP & CLFLUSH_FLAGS);
  		BUILD_BUG_ON((KMAP | CLFLUSH_FLAGS) & PAGE_MASK);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 5103067269b0..11b8e2735071 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -434,7 +434,6 @@ static inline void
  i915_gem_object_finish_access(struct drm_i915_gem_object *obj)
  {
  	i915_gem_object_unpin_pages(obj);
-	i915_gem_object_unlock(obj);
  }
static inline struct intel_engine_cs *
diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
index eb2011ccb92b..fff11327a8da 100644
--- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
+++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c
@@ -964,9 +964,10 @@ __cpu_check_shmem(struct drm_i915_gem_object *obj, u32 dword, u32 val)
  	unsigned long n;
  	int err;
+ i915_gem_object_lock(obj, NULL);
  	err = i915_gem_object_prepare_read(obj, &needs_flush);
  	if (err)
-		return err;
+		goto err_unlock;
for (n = 0; n < obj->base.size >> PAGE_SHIFT; ++n) {
  		u32 *ptr = kmap_atomic(i915_gem_object_get_page(obj, n));
@@ -986,6 +987,8 @@ __cpu_check_shmem(struct drm_i915_gem_object *obj, u32 dword, u32 val)
  	}
i915_gem_object_finish_access(obj);
+err_unlock:
+	i915_gem_object_unlock(obj);
return err;
  }
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
index 1de2959b153c..dcdfc396f2f8 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
@@ -27,9 +27,10 @@ static int cpu_set(struct context *ctx, unsigned long offset, u32 v)
  	u32 *cpu;
  	int err;
+ i915_gem_object_lock(ctx->obj, NULL);
  	err = i915_gem_object_prepare_write(ctx->obj, &needs_clflush);
  	if (err)
-		return err;
+		goto out;
page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
  	map = kmap_atomic(page);
@@ -46,7 +47,9 @@ static int cpu_set(struct context *ctx, unsigned long offset, u32 v)
  	kunmap_atomic(map);
  	i915_gem_object_finish_access(ctx->obj);
- return 0;
+out:
+	i915_gem_object_unlock(ctx->obj);
+	return err;
  }
static int cpu_get(struct context *ctx, unsigned long offset, u32 *v)
@@ -57,9 +60,10 @@ static int cpu_get(struct context *ctx, unsigned long offset, u32 *v)
  	u32 *cpu;
  	int err;
+ i915_gem_object_lock(ctx->obj, NULL);
  	err = i915_gem_object_prepare_read(ctx->obj, &needs_clflush);
  	if (err)
-		return err;
+		goto out;
page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
  	map = kmap_atomic(page);
@@ -73,7 +77,9 @@ static int cpu_get(struct context *ctx, unsigned long offset, u32 *v)
  	kunmap_atomic(map);
  	i915_gem_object_finish_access(ctx->obj);
- return 0;
+out:
+	i915_gem_object_unlock(ctx->obj);
+	return err;
  }
static int gtt_set(struct context *ctx, unsigned long offset, u32 v)
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
index 438c15ef2184..76671f587b9d 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
@@ -461,9 +461,10 @@ static int cpu_fill(struct drm_i915_gem_object *obj, u32 value)
  	unsigned int n, m, need_flush;
  	int err;
+ i915_gem_object_lock(obj, NULL);
  	err = i915_gem_object_prepare_write(obj, &need_flush);
  	if (err)
-		return err;
+		goto out;
for (n = 0; n < real_page_count(obj); n++) {
  		u32 *map;
@@ -479,7 +480,9 @@ static int cpu_fill(struct drm_i915_gem_object *obj, u32 value)
  	i915_gem_object_finish_access(obj);
  	obj->read_domains = I915_GEM_DOMAIN_GTT | I915_GEM_DOMAIN_CPU;
  	obj->write_domain = 0;
-	return 0;
+out:
+	i915_gem_object_unlock(obj);
+	return err;
  }
static noinline int cpu_check(struct drm_i915_gem_object *obj,
@@ -488,9 +491,10 @@ static noinline int cpu_check(struct drm_i915_gem_object *obj,
  	unsigned int n, m, needs_flush;
  	int err;
+ i915_gem_object_lock(obj, NULL);
  	err = i915_gem_object_prepare_read(obj, &needs_flush);
  	if (err)
-		return err;
+		goto out_unlock;
for (n = 0; n < real_page_count(obj); n++) {
  		u32 *map;
@@ -527,6 +531,8 @@ static noinline int cpu_check(struct drm_i915_gem_object *obj,
  	}
i915_gem_object_finish_access(obj);
+out_unlock:
+	i915_gem_object_unlock(obj);
  	return err;
  }
diff --git a/drivers/gpu/drm/i915/gvt/cmd_parser.c b/drivers/gpu/drm/i915/gvt/cmd_parser.c
index 943c8d232703..d0a599b51bfe 100644
--- a/drivers/gpu/drm/i915/gvt/cmd_parser.c
+++ b/drivers/gpu/drm/i915/gvt/cmd_parser.c
@@ -1923,6 +1923,7 @@ static int perform_bb_shadow(struct parser_exec_state *s)
  	if (ret)
  		goto err_unmap;
+ i915_gem_object_unlock(bb->obj);
  	INIT_LIST_HEAD(&bb->list);
  	list_add(&bb->list, &s->workload->shadow_bb);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 1e06752835e5..33f6f88c8b08 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -335,12 +335,20 @@ i915_gem_shmem_pread(struct drm_i915_gem_object *obj,
  	u64 remain;
  	int ret;
- ret = i915_gem_object_prepare_read(obj, &needs_clflush);
+	ret = i915_gem_object_lock_interruptible(obj, NULL);
  	if (ret)
  		return ret;
+ ret = i915_gem_object_prepare_read(obj, &needs_clflush);
+	if (ret) {
+		i915_gem_object_unlock(obj);
+		return ret;
+	}
+
  	fence = i915_gem_object_lock_fence(obj);
  	i915_gem_object_finish_access(obj);
+	i915_gem_object_unlock(obj);
+
  	if (!fence)
  		return -ENOMEM;
@@ -734,12 +742,20 @@ i915_gem_shmem_pwrite(struct drm_i915_gem_object *obj,
  	u64 remain;
  	int ret;
- ret = i915_gem_object_prepare_write(obj, &needs_clflush);
+	ret = i915_gem_object_lock_interruptible(obj, NULL);
  	if (ret)
  		return ret;
+ ret = i915_gem_object_prepare_write(obj, &needs_clflush);
+	if (ret) {
+		i915_gem_object_unlock(obj);
+		return ret;
+	}
+
  	fence = i915_gem_object_lock_fence(obj);
  	i915_gem_object_finish_access(obj);
+	i915_gem_object_unlock(obj);
+
  	if (!fence)
  		return -ENOMEM;

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko
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