Re: [PATCH 3/9] drm/i915: Make GEM contexts track DRM clients

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On Fri, Sep 04, 2020 at 01:59:28PM +0100, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

If we make GEM contexts keep a reference to i915_drm_client for the whole
of their lifetime, we can consolidate the current task pid and name usage
by getting it from the client.

v2:
* Don't bother supporting selftests contexts from debugfs. (Chris)

v3:
* Trivial rebase.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_context.c   | 19 +++++++++---
.../gpu/drm/i915/gem/i915_gem_context_types.h | 13 ++-------
drivers/gpu/drm/i915/i915_debugfs.c           | 29 +++++++------------
drivers/gpu/drm/i915/i915_gpu_error.c         | 22 ++++++++------
4 files changed, 41 insertions(+), 42 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 5919cc5f8348..ab8d25eda204 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -336,8 +336,13 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)

static void i915_gem_context_free(struct i915_gem_context *ctx)
{
+	struct i915_drm_client *client = ctx->client;
+
	GEM_BUG_ON(!i915_gem_context_is_closed(ctx));

+	if (client)
+		i915_drm_client_put(client);
+
	spin_lock(&ctx->i915->gem.contexts.lock);
	list_del(&ctx->link);
	spin_unlock(&ctx->i915->gem.contexts.lock);
@@ -348,7 +353,6 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
	if (ctx->timeline)
		intel_timeline_put(ctx->timeline);

-	put_pid(ctx->pid);
	mutex_destroy(&ctx->mutex);

	kfree_rcu(ctx, rcu);
@@ -936,6 +940,7 @@ static int gem_context_register(struct i915_gem_context *ctx,
				u32 *id)
{
	struct drm_i915_private *i915 = ctx->i915;
+	struct i915_drm_client *client;
	struct i915_address_space *vm;
	int ret;

@@ -947,9 +952,13 @@ static int gem_context_register(struct i915_gem_context *ctx,
		WRITE_ONCE(vm->file, fpriv); /* XXX */
	mutex_unlock(&ctx->mutex);

-	ctx->pid = get_task_pid(current, PIDTYPE_PID);
+	client = i915_drm_client_get(fpriv->client);
+
+	rcu_read_lock();
	snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",
-		 current->comm, pid_nr(ctx->pid));
+		 rcu_dereference(client->name),
+		 pid_nr(rcu_dereference(client->pid)));
+	rcu_read_unlock();

	/* And finally expose ourselves to userspace via the idr */
	ret = xa_alloc(&fpriv->context_xa, id, ctx, xa_limit_32b, GFP_KERNEL);
@@ -960,10 +969,12 @@ static int gem_context_register(struct i915_gem_context *ctx,
	list_add_tail(&ctx->link, &i915->gem.contexts.list);
	spin_unlock(&i915->gem.contexts.lock);

+	ctx->client = client;

as per 5f7cceabf104 ("drm/i915/gem: Delay tracking the GEM context until it is registered")
shouldn't you finish construct ctx before adding it to the list?

Lucas De Marchi

+
	return 0;

err_pid:
-	put_pid(fetch_and_zero(&ctx->pid));
+	i915_drm_client_put(client);
	return ret;
}

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
index ae14ca24a11f..31a6a30f7ea8 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h
@@ -96,20 +96,13 @@ struct i915_gem_context {
	 */
	struct i915_address_space __rcu *vm;

-	/**
-	 * @pid: process id of creator
-	 *
-	 * Note that who created the context may not be the principle user,
-	 * as the context may be shared across a local socket. However,
-	 * that should only affect the default context, all contexts created
-	 * explicitly by the client are expected to be isolated.
-	 */
-	struct pid *pid;
-
	/** link: place with &drm_i915_private.context_list */
	struct list_head link;
	struct llist_node free_link;

+	/** client: struct i915_drm_client */
+	struct i915_drm_client *client;
+
	/**
	 * @ref: reference count
	 *
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 784219962193..1df87d9735fc 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -331,17 +331,15 @@ static void print_context_stats(struct seq_file *m,
				.vm = rcu_access_pointer(ctx->vm),
			};
			struct drm_file *file = ctx->file_priv->file;
-			struct task_struct *task;
			char name[80];

			rcu_read_lock();
+
			idr_for_each(&file->object_idr, per_file_stats, &stats);
-			rcu_read_unlock();

-			rcu_read_lock();
-			task = pid_task(ctx->pid ?: file->pid, PIDTYPE_PID);
			snprintf(name, sizeof(name), "%s",
-				 task ? task->comm : "<unknown>");
+				 rcu_dereference(ctx->client->name));
+
			rcu_read_unlock();

			print_file_stats(m, name, stats);
@@ -1073,20 +1071,13 @@ static int i915_context_status(struct seq_file *m, void *unused)
		spin_unlock(&i915->gem.contexts.lock);

		seq_puts(m, "HW context ");
-		if (ctx->pid) {
-			struct task_struct *task;
-
-			task = get_pid_task(ctx->pid, PIDTYPE_PID);
-			if (task) {
-				seq_printf(m, "(%s [%d]) ",
-					   task->comm, task->pid);
-				put_task_struct(task);
-			}
-		} else if (IS_ERR(ctx->file_priv)) {
-			seq_puts(m, "(deleted) ");
-		} else {
-			seq_puts(m, "(kernel) ");
-		}
+
+		rcu_read_lock();
+		seq_printf(m, "(%s [%d]) %s",
+			   rcu_dereference(ctx->client->name),
+			   pid_nr(rcu_dereference(ctx->client->pid)),
+			   ctx->client->closed ? "(closed) " : "");
+		rcu_read_unlock();

		seq_putc(m, ctx->remap_slice ? 'R' : 'r');
		seq_putc(m, '\n');
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 3e6cbb0d1150..8e468942f943 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1229,7 +1229,9 @@ static void record_request(const struct i915_request *request,

		ctx = rcu_dereference(request->context->gem_context);
		if (ctx)
-			erq->pid = pid_nr(ctx->pid);
+			erq->pid = I915_SELFTEST_ONLY(!ctx->client) ?
+				   0 :
+				   pid_nr(rcu_dereference(ctx->client->pid));
	}
	rcu_read_unlock();
}
@@ -1250,23 +1252,25 @@ static bool record_context(struct i915_gem_context_coredump *e,
			   const struct i915_request *rq)
{
	struct i915_gem_context *ctx;
-	struct task_struct *task;
	bool simulated;

	rcu_read_lock();
+
	ctx = rcu_dereference(rq->context->gem_context);
	if (ctx && !kref_get_unless_zero(&ctx->ref))
		ctx = NULL;
-	rcu_read_unlock();
-	if (!ctx)
+	if (!ctx) {
+		rcu_read_unlock();
		return true;
+	}

-	rcu_read_lock();
-	task = pid_task(ctx->pid, PIDTYPE_PID);
-	if (task) {
-		strcpy(e->comm, task->comm);
-		e->pid = task->pid;
+	if (I915_SELFTEST_ONLY(!ctx->client)) {
+		strcpy(e->comm, "[kernel]");
+	} else {
+		strcpy(e->comm, rcu_dereference(ctx->client->name));
+		e->pid = pid_nr(rcu_dereference(ctx->client->pid));
	}
+
	rcu_read_unlock();

	e->sched_attr = ctx->sched;
--
2.25.1

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