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cgroup: make for_each_subsys() useable under cgroup_root_mutex 

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@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: kbuild test robot <fengguang.wu@intel.com>
hifive-unleashed-5.1
Tejun Heo 2013-12-06 15:11:56 -05:00
parent 87fb54f1b5
commit 780cd8b347
1 changed files with 20 additions and 6 deletions
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26
kernel/cgroup.c
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@ -98,6 +98,14 @@ 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
/*
* cgroup destruction makes heavy use of work items and there can be a lot
* of concurrent destructions. Use a separate workqueue so that cgroup
@ -237,14 +245,15 @@ static int notify_on_release(const struct cgroup *cgrp)
/**
* 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
/**
@ -4592,6 +4601,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
cgroup_init_cftsets(ss);
mutex_lock(&cgroup_mutex);
mutex_lock(&cgroup_root_mutex);
cgroup_subsys[ss->subsys_id] = ss;
/*
@ -4641,10 +4651,12 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
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);
@ -4674,6 +4686,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
BUG_ON(ss->root != &cgroup_dummy_root);
mutex_lock(&cgroup_mutex);
mutex_lock(&cgroup_root_mutex);
offline_css(cgroup_css(cgroup_dummy_top, ss));
@ -4708,6 +4721,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
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);