On Thu, Mar 19, 2015 at 11:04:33PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 19, 2015 at 01:58:33PM -0700, Andrew Morton wrote:
> > OK. This code is basically required to support perf/ftrace and
> > modules, yes? Presumably small and space-constrained systems aren't
> > using either, so they don't take the hit.
> >
> > However CONFIG_MODULES systems which aren't using perf/ftrace _do_ take
> > a hit. How many systems are we talking here? All non-x86?
>
> No, there's plenty !x86 systems that have NMI and perf/ftrace, in fact,
> ARM has them (FIQ) and there's event some ARM chips that use them for
> perf (i.MX6 is one).
>
> But sure, we could make this depend on CONFIG_PERF_EVENTS ||
> CONFIG_TRACING.
A little something like so.
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
kernel/module.c | 30 ++++++++++++++++++++++++++++--
1 file changed, 28 insertions(+), 2 deletions(-)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -102,6 +102,8 @@ DEFINE_MUTEX(module_mutex);
EXPORT_SYMBOL_GPL(module_mutex);
static LIST_HEAD(modules);
+#if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_TRACING)
+
/*
* Use a latched RB-tree for __module_address(); this allows us to use
* RCU-sched lookups of the address from any context.
@@ -109,6 +111,10 @@ static LIST_HEAD(modules);
* Because modules have two address ranges: init and core, we need two
* latch_tree_nodes entries. We use the order they appear in struct module to
* determine if we need to use the init or core values for the comparisons.
+ *
+ * This is conditional on PERF_EVENTS || TRACING because those can really hit
+ * __module_address() hard by doing a lot of stack unwinding; potentially from
+ * NMI context.
*/
static __always_inline unsigned long __mod_tree_val(struct latch_tree_node *n)
@@ -185,7 +191,7 @@ static void mod_tree_remove(struct modul
mod_tree_remove_init(mod);
}
-static struct module *mod_tree_find(unsigned long addr)
+static struct module *mod_find(unsigned long addr)
{
struct latch_tree_node *ltn;
@@ -194,6 +200,26 @@ static struct module *mod_tree_find(unsi
return ltn ? ltn->priv : NULL;
}
+#else /* !(PERF_EVENTS || TRACING) */
+
+static void mod_tree_insert(struct module *mod) { }
+static void mod_tree_remove_init(struct module *mod) { }
+static void mod_tree_remove(struct module *mod) { }
+
+static struct module *mod_find(unsigned long addr)
+{
+ struct module *mod;
+
+ list_for_each_entry_rcu(mod, &modules, list) {
+ if (within_module(addr, mod))
+ return mod;
+ }
+
+ return NULL;
+}
+
+#endif /* !(PERF_EVENTS || TRACING) */
+
#ifdef CONFIG_KGDB_KDB
struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
#endif /* CONFIG_KGDB_KDB */
@@ -3939,7 +3965,7 @@ struct module *__module_address(unsigned
module_assert_mutex_or_preempt();
- mod = mod_tree_find(addr);
+ mod = mod_find(addr);
if (mod) {
BUG_ON(!within_module(addr, mod));
if (mod->state == MODULE_STATE_UNFORMED)
--
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