@@ -1436,6 +1436,10 @@ void i915_gem_init__contexts(struct drm_i915_private *i915)
init_contexts(&i915->gem.contexts);
}
+/*
+ * Note that this implicitly consumes the ctx reference, by placing
+ * the ctx in the context_xa.
+ */
static void gem_context_register(struct i915_gem_context *ctx,
struct drm_i915_file_private *fpriv,
u32 id)
@@ -1449,13 +1453,13 @@ static void gem_context_register(struct i915_gem_context *ctx,
snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",
current->comm, pid_nr(ctx->pid));
- /* And finally expose ourselves to userspace via the idr */
- old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL);
- WARN_ON(old);
-
spin_lock(&i915->gem.contexts.lock);
list_add_tail(&ctx->link, &i915->gem.contexts.list);
spin_unlock(&i915->gem.contexts.lock);
+
+ /* And finally expose ourselves to userspace via the idr */
+ old = xa_store(&fpriv->context_xa, id, ctx, GFP_KERNEL);
+ WARN_ON(old);
}
int i915_gem_context_open(struct drm_i915_private *i915,
@@ -1932,14 +1936,22 @@ finalize_create_context_locked(struct drm_i915_file_private *file_priv,
if (IS_ERR(ctx))
return ctx;
+ /*
+ * One for the xarray and one for the caller. We need to grab
+ * the reference *prior* to making the ctx visble to userspace
+ * in gem_context_register(), as at any point after that
+ * userspace can try to race us with another thread destroying
+ * the context under our feet.
+ */
+ i915_gem_context_get(ctx);
+
gem_context_register(ctx, file_priv, id);
old = xa_erase(&file_priv->proto_context_xa, id);
GEM_BUG_ON(old != pc);
proto_context_close(pc);
- /* One for the xarray and one for the caller */
- return i915_gem_context_get(ctx);
+ return ctx;
}
struct i915_gem_context *