From 858d5881564026cbc4e6f5e25ae878a27df5d4c9 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Mon, 28 Dec 2015 19:23:06 +0900 Subject: [PATCH] clk: avoid circular clock topology 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 Reviewed-by: Vladimir Zapolskiy Signed-off-by: Stephen Boyd --- drivers/clk/clk.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index dee9c528ea83..5a1507498e05 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -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); /* -- 2.20.1