perf: Annotate inherited event ctx->mutex recursion (8b10c5e2) · Commits · e / devices / android_kernel_fairphone_FP4

kernel/events/core.c

+33 −8

Original line number	Original line	Diff line number	Diff line
	@@ -913,10 +913,30 @@ static void put_ctx(struct perf_event_context *ctx)
	* Those places that change perf_event::ctx will hold both		* Those places that change perf_event::ctx will hold both
	* perf_event_ctx::mutex of the 'old' and 'new' ctx value.		* perf_event_ctx::mutex of the 'old' and 'new' ctx value.
	*		*
	* Lock ordering is by mutex address. There is one other site where		* Lock ordering is by mutex address. There are two other sites where
	* perf_event_context::mutex nests and that is put_event(). But remember that		* perf_event_context::mutex nests and those are:
	* that is a parent<->child context relation, and migration does not affect		*
	* children, therefore these two orderings should not interact.		* - perf_event_exit_task_context() [ child , 0 ]
			* __perf_event_exit_task()
			* sync_child_event()
			* put_event() [ parent, 1 ]
			*
			* - perf_event_init_context() [ parent, 0 ]
			* inherit_task_group()
			* inherit_group()
			* inherit_event()
			* perf_event_alloc()
			* perf_init_event()
			* perf_try_init_event() [ child , 1 ]
			*
			* While it appears there is an obvious deadlock here -- the parent and child
			* nesting levels are inverted between the two. This is in fact safe because
			* life-time rules separate them. That is an exiting task cannot fork, and a
			* spawning task cannot (yet) exit.
			*
			* But remember that that these are parent<->child context relations, and
			* migration does not affect children, therefore these two orderings should not
			* interact.
	*		*
	* The change in perf_event::ctx does not affect children (as claimed above)		* The change in perf_event::ctx does not affect children (as claimed above)
	* because the sys_perf_event_open() case will install a new event and break		* because the sys_perf_event_open() case will install a new event and break
	@@ -3657,9 +3677,6 @@ static void perf_remove_from_owner(struct perf_event *event)
	}		}
	}		}

	/*
	* Called when the last reference to the file is gone.
	*/
	static void put_event(struct perf_event *event)		static void put_event(struct perf_event *event)
	{		{
	struct perf_event_context *ctx;		struct perf_event_context *ctx;
	@@ -3697,6 +3714,9 @@ int perf_event_release_kernel(struct perf_event *event)
	}		}
	EXPORT_SYMBOL_GPL(perf_event_release_kernel);		EXPORT_SYMBOL_GPL(perf_event_release_kernel);

			/*
			* Called when the last reference to the file is gone.
			*/
	static int perf_release(struct inode inode, struct file file)		static int perf_release(struct inode inode, struct file file)
	{		{
	put_event(file->private_data);		put_event(file->private_data);
	@@ -7364,7 +7384,12 @@ static int perf_try_init_event(struct pmu pmu, struct perf_event event)
	return -ENODEV;		return -ENODEV;

	if (event->group_leader != event) {		if (event->group_leader != event) {
	ctx = perf_event_ctx_lock(event->group_leader);		/*
			* This ctx->mutex can nest when we're called through
			* inheritance. See the perf_event_ctx_lock_nested() comment.
			*/
			ctx = perf_event_ctx_lock_nested(event->group_leader,
			SINGLE_DEPTH_NESTING);
	BUG_ON(!ctx);		BUG_ON(!ctx);
	}		}