We want to use for_each_subsys() in cgroupfs_root handling where only
cgroup_root_mutex is held. The only way cgroup_subsys[] can change is
through module load/unload, make cgroup_[un]load_subsys() grab
cgroup_root_mutex too and update the lockdep annotation in
for_each_subsys() to allow either cgroup_mutex or cgroup_root_mutex.
* Lockdep annotation is moved from inner 'if' condition to outer 'for'
init caluse. There's no reason to execute the assertion every loop.
* Loop index @i is renamed to @ssid. Indices iterating through subsys
will be [re]named to @ssid gradually.
v2: cgroup_assert_mutex_or_root_locked() caused build failure if
!CONFIG_LOCKEDP. Conditionalize its definition. The build failure
was reported by kbuild test bot.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: kbuild test robot <fengguang.wu@xxxxxxxxx>
---
kernel/cgroup.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -93,6 +93,14 @@ static DEFINE_MUTEX(cgroup_root_mutex);
lockdep_is_held(&cgroup_mutex), \
"cgroup_mutex or RCU read lock required");
+#ifdef CONFIG_LOCKDEP
+#define cgroup_assert_mutex_or_root_locked() \
+ WARN_ON_ONCE(debug_locks && (!lockdep_is_held(&cgroup_mutex) && \
+ !lockdep_is_held(&cgroup_root_mutex)))
+#else
+#define cgroup_assert_mutex_or_root_locked() do { } while (0)
+#endif
+
/*
* Generate an array of cgroup subsystem pointers. At boot time, this is
* populated with the built in subsystems, and modular subsystems are
@@ -291,14 +299,15 @@ static int notify_on_release(const struc
/**
* for_each_subsys - iterate all loaded cgroup subsystems
* @ss: the iteration cursor
- * @i: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
+ * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
*
- * Should be called under cgroup_mutex.
+ * Iterates through all loaded subsystems. Should be called under
+ * cgroup_mutex or cgroup_root_mutex.
*/
-#define for_each_subsys(ss, i) \
- for ((i) = 0; (i) < CGROUP_SUBSYS_COUNT; (i)++) \
- if (({ lockdep_assert_held(&cgroup_mutex); \
- !((ss) = cgroup_subsys[i]); })) { } \
+#define for_each_subsys(ss, ssid) \
+ for (({ cgroup_assert_mutex_or_root_locked(); (ssid) = 0; }); \
+ (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \
+ if (!((ss) = cgroup_subsys[(ssid)])) { } \
else
/**
@@ -4911,6 +4920,7 @@ int __init_or_module cgroup_load_subsys(
cgroup_init_cftsets(ss);
mutex_lock(&cgroup_mutex);
+ mutex_lock(&cgroup_root_mutex);
cgroup_subsys[ss->subsys_id] = ss;
/*
@@ -4966,10 +4976,12 @@ int __init_or_module cgroup_load_subsys(
goto err_unload;
/* success! */
+ mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
return 0;
err_unload:
+ mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
/* @ss can't be mounted here as try_module_get() would fail */
cgroup_unload_subsys(ss);
@@ -4999,6 +5011,7 @@ void cgroup_unload_subsys(struct cgroup_
BUG_ON(ss->root != &cgroup_dummy_root);
mutex_lock(&cgroup_mutex);
+ mutex_lock(&cgroup_root_mutex);
offline_css(cgroup_css(cgroup_dummy_top, ss));
@@ -5037,6 +5050,7 @@ void cgroup_unload_subsys(struct cgroup_
ss->css_free(cgroup_css(cgroup_dummy_top, ss));
RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);
+ mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
}
EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
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