[PATCH v3 0/2] drm/imagination: Break an obejct reference loop

[PATCH v3 0/2] drm/imagination: Break an obejct reference loop

[Matt Coster]

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When remaining resources are being cleaned up on driver close,
outstanding VM mappings may result in resources being leaked, due
to an object reference loop, as shown below, with each object (or
set of objects) referencing the object below it:

    PVR GEM Object
    GPU scheduler "finished" fence
    GPU scheduler "scheduled" fence
    PVR driver "done" fence
    PVR Context
    PVR VM Context
    PVR VM Mappings
    PVR GEM Object

The reference that the PVR VM Context has on the VM mappings is a
soft one, in the sense that the freeing of outstanding VM mappings
is done as part of VM context destruction; no reference counts are
involved, as is the case for all the other references in the loop.

To break the reference loop during cleanup, free the outstanding
VM mappings before destroying the PVR Context associated with the
VM context.

This is facilitated by tracking the live contexts associated with each
list, implemented in a separate patch to make the main patch cleaner
and easier to grok.

---

Changes in v1 -> v2:
 - [PATCH 1/2] Add justification to the commit message so it stands on
   its own (e.g. during bisect)

Changes in v2 -> v3:
 - [ALL] Add Frank's Rb [1][2]
 - [ALL] Add Cc: stable tag

[1]: https://lore.kernel.org/dri-devel/1a206b08485a1ebea0aeff5306c0f5b6eb7c315d.camel@imgtec.com/
[2]: https://lore.kernel.org/dri-devel/b75e658cc5ce9ac24df2c31c1a6fd798a5f3a87f.camel@imgtec.com/

---

Brendan King (2):
  drm/imagination: Add a per-file PVR context list
  drm/imagination: Break an object reference loop

 drivers/gpu/drm/imagination/pvr_context.c | 33 +++++++++++++++++++++++
 drivers/gpu/drm/imagination/pvr_context.h | 21 +++++++++++++++
 drivers/gpu/drm/imagination/pvr_device.h  | 10 +++++++
 drivers/gpu/drm/imagination/pvr_drv.c     |  3 +++
 drivers/gpu/drm/imagination/pvr_vm.c      | 22 ++++++++++++---
 drivers/gpu/drm/imagination/pvr_vm.h      |  1 +
 6 files changed, 86 insertions(+), 4 deletions(-)


base-commit: 83f000784844cb9d4669ef1a3366479db3197b33
-- 
2.47.0



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[PATCH v3 1/2] drm/imagination: Add a per-file PVR context list

[Matt Coster]

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From: Brendan King <brendan.king@imgtec.com>

This adds a linked list of VM contexts which is needed for the next patch
to be able to correctly track VM contexts for destruction on file close.

It is only safe for VM contexts to be removed from the list and destroyed
when not in interrupt context.

Signed-off-by: Brendan King <brendan.king@imgtec.com>
Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Cc: stable@vger.kernel.org
---
Changes in v1 -> v2:
 - Add justification to the commit message so it stands on its own (e.g.
   during bisect)

Changes in v2 -> v3:
 - Add Frank's Rb [1]
 - Add Cc: stable tag

[1]: https://lore.kernel.org/dri-devel/1a206b08485a1ebea0aeff5306c0f5b6eb7c315d.camel@imgtec.com/
---
 drivers/gpu/drm/imagination/pvr_context.c | 14 ++++++++++++++
 drivers/gpu/drm/imagination/pvr_context.h |  3 +++
 drivers/gpu/drm/imagination/pvr_device.h  | 10 ++++++++++
 drivers/gpu/drm/imagination/pvr_drv.c     |  3 +++
 4 files changed, 30 insertions(+)

diff --git a/drivers/gpu/drm/imagination/pvr_context.c b/drivers/gpu/drm/imagination/pvr_context.c
index eded5e955cc0..255c93582734 100644
--- a/drivers/gpu/drm/imagination/pvr_context.c
+++ b/drivers/gpu/drm/imagination/pvr_context.c
@@ -17,10 +17,14 @@
 
 #include <drm/drm_auth.h>
 #include <drm/drm_managed.h>
+
+#include <linux/bug.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
+#include <linux/list.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/xarray.h>
@@ -354,6 +358,10 @@ int pvr_context_create(struct pvr_file *pvr_file, struct drm_pvr_ioctl_create_co
 		return err;
 	}
 
+	spin_lock(&pvr_dev->ctx_list_lock);
+	list_add_tail(&ctx->file_link, &pvr_file->contexts);
+	spin_unlock(&pvr_dev->ctx_list_lock);
+
 	return 0;
 
 err_destroy_fw_obj:
@@ -380,6 +388,11 @@ pvr_context_release(struct kref *ref_count)
 		container_of(ref_count, struct pvr_context, ref_count);
 	struct pvr_device *pvr_dev = ctx->pvr_dev;
 
+	WARN_ON(in_interrupt());
+	spin_lock(&pvr_dev->ctx_list_lock);
+	list_del(&ctx->file_link);
+	spin_unlock(&pvr_dev->ctx_list_lock);
+
 	xa_erase(&pvr_dev->ctx_ids, ctx->ctx_id);
 	pvr_context_destroy_queues(ctx);
 	pvr_fw_object_destroy(ctx->fw_obj);
@@ -451,6 +464,7 @@ void pvr_destroy_contexts_for_file(struct pvr_file *pvr_file)
 void pvr_context_device_init(struct pvr_device *pvr_dev)
 {
 	xa_init_flags(&pvr_dev->ctx_ids, XA_FLAGS_ALLOC1);
+	spin_lock_init(&pvr_dev->ctx_list_lock);
 }
 
 /**
diff --git a/drivers/gpu/drm/imagination/pvr_context.h b/drivers/gpu/drm/imagination/pvr_context.h
index 0c7b97dfa6ba..a5b0a82a54a1 100644
--- a/drivers/gpu/drm/imagination/pvr_context.h
+++ b/drivers/gpu/drm/imagination/pvr_context.h
@@ -85,6 +85,9 @@ struct pvr_context {
 		/** @compute: Transfer queue. */
 		struct pvr_queue *transfer;
 	} queues;
+
+	/** @file_link: pvr_file PVR context list link. */
+	struct list_head file_link;
 };
 
 static __always_inline struct pvr_queue *
diff --git a/drivers/gpu/drm/imagination/pvr_device.h b/drivers/gpu/drm/imagination/pvr_device.h
index b574e23d484b..6d0dfacb677b 100644
--- a/drivers/gpu/drm/imagination/pvr_device.h
+++ b/drivers/gpu/drm/imagination/pvr_device.h
@@ -23,6 +23,7 @@
 #include <linux/kernel.h>
 #include <linux/math.h>
 #include <linux/mutex.h>
+#include <linux/spinlock_types.h>
 #include <linux/timer.h>
 #include <linux/types.h>
 #include <linux/wait.h>
@@ -293,6 +294,12 @@ struct pvr_device {
 
 	/** @sched_wq: Workqueue for schedulers. */
 	struct workqueue_struct *sched_wq;
+
+	/**
+	 * @ctx_list_lock: Lock to be held when accessing the context list in
+	 *  struct pvr_file.
+	 */
+	spinlock_t ctx_list_lock;
 };
 
 /**
@@ -344,6 +351,9 @@ struct pvr_file {
 	 * This array is used to allocate handles returned to userspace.
 	 */
 	struct xarray vm_ctx_handles;
+
+	/** @contexts: PVR context list. */
+	struct list_head contexts;
 };
 
 /**
diff --git a/drivers/gpu/drm/imagination/pvr_drv.c b/drivers/gpu/drm/imagination/pvr_drv.c
index 1a0cb7aa9cea..fb17196e05f4 100644
--- a/drivers/gpu/drm/imagination/pvr_drv.c
+++ b/drivers/gpu/drm/imagination/pvr_drv.c
@@ -28,6 +28,7 @@
 #include <linux/export.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
+#include <linux/list.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
@@ -1326,6 +1327,8 @@ pvr_drm_driver_open(struct drm_device *drm_dev, struct drm_file *file)
 	 */
 	pvr_file->pvr_dev = pvr_dev;
 
+	INIT_LIST_HEAD(&pvr_file->contexts);
+
 	xa_init_flags(&pvr_file->ctx_handles, XA_FLAGS_ALLOC1);
 	xa_init_flags(&pvr_file->free_list_handles, XA_FLAGS_ALLOC1);
 	xa_init_flags(&pvr_file->hwrt_handles, XA_FLAGS_ALLOC1);
-- 
2.47.0



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[PATCH v3 2/2] drm/imagination: Break an object reference loop

[Matt Coster]

[-- Attachment #1.1: Type: text/plain, Size: 6197 bytes --]

From: Brendan King <brendan.king@imgtec.com>

When remaining resources are being cleaned up on driver close,
outstanding VM mappings may result in resources being leaked, due
to an object reference loop, as shown below, with each object (or
set of objects) referencing the object below it:

    PVR GEM Object
    GPU scheduler "finished" fence
    GPU scheduler “scheduled” fence
    PVR driver “done” fence
    PVR Context
    PVR VM Context
    PVR VM Mappings
    PVR GEM Object

The reference that the PVR VM Context has on the VM mappings is a
soft one, in the sense that the freeing of outstanding VM mappings
is done as part of VM context destruction; no reference counts are
involved, as is the case for all the other references in the loop.

To break the reference loop during cleanup, free the outstanding
VM mappings before destroying the PVR Context associated with the
VM context.

Signed-off-by: Brendan King <brendan.king@imgtec.com>
Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Cc: stable@vger.kernel.org
---
Changes in v1 -> v2:
 - None

Changes in v2 -> v3:
 - Add Frank's Rb [1]
 - Add Cc: stable tag

[1]: https://lore.kernel.org/dri-devel/b75e658cc5ce9ac24df2c31c1a6fd798a5f3a87f.camel@imgtec.com/
---
 drivers/gpu/drm/imagination/pvr_context.c | 19 +++++++++++++++++++
 drivers/gpu/drm/imagination/pvr_context.h | 18 ++++++++++++++++++
 drivers/gpu/drm/imagination/pvr_vm.c      | 22 ++++++++++++++++++----
 drivers/gpu/drm/imagination/pvr_vm.h      |  1 +
 4 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/imagination/pvr_context.c b/drivers/gpu/drm/imagination/pvr_context.c
index 255c93582734..4cb3494c0bb2 100644
--- a/drivers/gpu/drm/imagination/pvr_context.c
+++ b/drivers/gpu/drm/imagination/pvr_context.c
@@ -450,11 +450,30 @@ pvr_context_destroy(struct pvr_file *pvr_file, u32 handle)
  */
 void pvr_destroy_contexts_for_file(struct pvr_file *pvr_file)
 {
+	struct pvr_device *pvr_dev = pvr_file->pvr_dev;
 	struct pvr_context *ctx;
 	unsigned long handle;
 
 	xa_for_each(&pvr_file->ctx_handles, handle, ctx)
 		pvr_context_destroy(pvr_file, handle);
+
+	spin_lock(&pvr_dev->ctx_list_lock);
+	ctx = list_first_entry(&pvr_file->contexts, struct pvr_context, file_link);
+
+	while (!list_entry_is_head(ctx, &pvr_file->contexts, file_link)) {
+		list_del_init(&ctx->file_link);
+
+		if (pvr_context_get_if_referenced(ctx)) {
+			spin_unlock(&pvr_dev->ctx_list_lock);
+
+			pvr_vm_unmap_all(ctx->vm_ctx);
+
+			pvr_context_put(ctx);
+			spin_lock(&pvr_dev->ctx_list_lock);
+		}
+		ctx = list_first_entry(&pvr_file->contexts, struct pvr_context, file_link);
+	}
+	spin_unlock(&pvr_dev->ctx_list_lock);
 }
 
 /**
diff --git a/drivers/gpu/drm/imagination/pvr_context.h b/drivers/gpu/drm/imagination/pvr_context.h
index a5b0a82a54a1..07afa179cdf4 100644
--- a/drivers/gpu/drm/imagination/pvr_context.h
+++ b/drivers/gpu/drm/imagination/pvr_context.h
@@ -126,6 +126,24 @@ pvr_context_get(struct pvr_context *ctx)
 	return ctx;
 }
 
+/**
+ * pvr_context_get_if_referenced() - Take an additional reference on a still
+ * referenced context.
+ * @ctx: Context pointer.
+ *
+ * Call pvr_context_put() to release.
+ *
+ * Returns:
+ *  * True on success, or
+ *  * false if no context pointer passed, or the context wasn't still
+ *  * referenced.
+ */
+static __always_inline bool
+pvr_context_get_if_referenced(struct pvr_context *ctx)
+{
+	return ctx != NULL && kref_get_unless_zero(&ctx->ref_count) != 0;
+}
+
 /**
  * pvr_context_lookup() - Lookup context pointer from handle and file.
  * @pvr_file: Pointer to pvr_file structure.
diff --git a/drivers/gpu/drm/imagination/pvr_vm.c b/drivers/gpu/drm/imagination/pvr_vm.c
index 97c0f772ed65..7bd6ba4c6e8a 100644
--- a/drivers/gpu/drm/imagination/pvr_vm.c
+++ b/drivers/gpu/drm/imagination/pvr_vm.c
@@ -14,6 +14,7 @@
 #include <drm/drm_gem.h>
 #include <drm/drm_gpuvm.h>
 
+#include <linux/bug.h>
 #include <linux/container_of.h>
 #include <linux/err.h>
 #include <linux/errno.h>
@@ -597,12 +598,26 @@ pvr_vm_create_context(struct pvr_device *pvr_dev, bool is_userspace_context)
 }
 
 /**
- * pvr_vm_context_release() - Teardown a VM context.
- * @ref_count: Pointer to reference counter of the VM context.
+ * pvr_vm_unmap_all() - Unmap all mappings associated with a VM context.
+ * @vm_ctx: Target VM context.
  *
  * This function ensures that no mappings are left dangling by unmapping them
  * all in order of ascending device-virtual address.
  */
+void
+pvr_vm_unmap_all(struct pvr_vm_context *vm_ctx)
+{
+	WARN_ON(pvr_vm_unmap(vm_ctx, vm_ctx->gpuvm_mgr.mm_start,
+			     vm_ctx->gpuvm_mgr.mm_range));
+}
+
+/**
+ * pvr_vm_context_release() - Teardown a VM context.
+ * @ref_count: Pointer to reference counter of the VM context.
+ *
+ * This function also ensures that no mappings are left dangling by calling
+ * pvr_vm_unmap_all.
+ */
 static void
 pvr_vm_context_release(struct kref *ref_count)
 {
@@ -612,8 +627,7 @@ pvr_vm_context_release(struct kref *ref_count)
 	if (vm_ctx->fw_mem_ctx_obj)
 		pvr_fw_object_destroy(vm_ctx->fw_mem_ctx_obj);
 
-	WARN_ON(pvr_vm_unmap(vm_ctx, vm_ctx->gpuvm_mgr.mm_start,
-			     vm_ctx->gpuvm_mgr.mm_range));
+	pvr_vm_unmap_all(vm_ctx);
 
 	pvr_mmu_context_destroy(vm_ctx->mmu_ctx);
 	drm_gem_private_object_fini(&vm_ctx->dummy_gem);
diff --git a/drivers/gpu/drm/imagination/pvr_vm.h b/drivers/gpu/drm/imagination/pvr_vm.h
index f2a6463f2b05..79406243617c 100644
--- a/drivers/gpu/drm/imagination/pvr_vm.h
+++ b/drivers/gpu/drm/imagination/pvr_vm.h
@@ -39,6 +39,7 @@ int pvr_vm_map(struct pvr_vm_context *vm_ctx,
 	       struct pvr_gem_object *pvr_obj, u64 pvr_obj_offset,
 	       u64 device_addr, u64 size);
 int pvr_vm_unmap(struct pvr_vm_context *vm_ctx, u64 device_addr, u64 size);
+void pvr_vm_unmap_all(struct pvr_vm_context *vm_ctx);
 
 dma_addr_t pvr_vm_get_page_table_root_addr(struct pvr_vm_context *vm_ctx);
 struct dma_resv *pvr_vm_get_dma_resv(struct pvr_vm_context *vm_ctx);
-- 
2.47.0



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