clk: avoid circular clock topology (858d5881) · Commits · 戴 / test

Currently, clk_register() never checks a circular parent looping, but clock providers could register such an insane clock topology. For example, "clk_a" could have "clk_b" as a parent, and vice versa. In this case, clk_core_reparent() creates a circular parent list and __clk_recalc_accuracies() calls itself recursively forever. The core infrastructure should be kind enough to bail out, showing an appropriate error message in such a case. This helps to easily find a bug in clock providers. (uh, I made such a silly mistake when I was implementing my clock providers first. I was upset because the kernel did not respond, without any error message.) This commit adds a new helper function, __clk_is_ancestor(). It returns true if the second argument is a possible ancestor of the first one. If a clock core is a possible ancestor of itself, it would make a loop when it were registered. That should be detected as an error. Signed-off-by:

Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by:

Vladimir Zapolskiy <vz@mleia.com> Signed-off-by:

Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/clk.c

+40 −0

Original line number	Diff line number	Diff line
		@@ -2252,6 +2252,38 @@ static inline void clk_debug_unregister(struct clk_core *core)
		}
		#endif

		/**
		* __clk_is_ancestor - check if a clk_core is a possible ancestor of another
		* @core: clock core
		* @ancestor: ancestor clock core
		*
		* Returns true if there is a possibility that @ancestor can be an ancestor
		* of @core, false otherwise.
		*
		* This function can be used against @core or @ancestor that has not been
		* registered yet.
		*/
		static bool __clk_is_ancestor(struct clk_core core, struct clk_core ancestor)
		{
		struct clk_core *parent;
		int i;

		for (i = 0; i < core->num_parents; i++) {
		parent = clk_core_get_parent_by_index(core, i);
		/*
		* If ancestor has not been added to clk_{root,orphan}_list
		* yet, clk_core_lookup() cannot find it. If parent is NULL,
		* compare the name strings, too.
		*/
		if ((parent && (parent == ancestor \|\|
		__clk_is_ancestor(parent, ancestor))) \|\|
		(!parent && !strcmp(core->parent_names[i], ancestor->name)))
		return true;
		}

		return false;
		}

		/**
		* __clk_core_init - initialize the data structures in a struct clk_core
		* @core: clk_core being initialized
		@@ -2317,6 +2349,14 @@ static int __clk_core_init(struct clk_core *core)
		"%s: invalid NULL in %s's .parent_names\n",
		__func__, core->name);

		/* If core is an ancestor of itself, it would make a loop. */
		if (__clk_is_ancestor(core, core)) {
		pr_err("%s: %s would create circular parent\n", __func__,
		core->name);
		ret = -EINVAL;
		goto out;
		}

		core->parent = __clk_init_parent(core);

		/*

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