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authorTejun Heo <tj@kernel.org>2012-11-05 09:21:51 -0800
committerTejun Heo <tj@kernel.org>2012-11-05 09:21:51 -0800
commit1db1e31b1ee3ae126ef98f39083b5f213c7b41bf (patch)
tree98328124d3b8b08b6db894c79d0e79b3a42417bf /kernel/cgroup.c
parent5d8f72b55c275677865de670fa147ed318191d81 (diff)
parentbcf6de1b9129531215d26dd9af8331e84973bc52 (diff)
downloadop-kernel-dev-1db1e31b1ee3ae126ef98f39083b5f213c7b41bf.zip
op-kernel-dev-1db1e31b1ee3ae126ef98f39083b5f213c7b41bf.tar.gz
Merge branch 'cgroup-rmdir-updates' into cgroup/for-3.8
Pull rmdir updates into for-3.8 so that further callback updates can be put on top. This pull created a trivial conflict between the following two commits. 8c7f6edbda ("cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them") ed95779340 ("cgroup: kill cgroup_subsys->__DEPRECATED_clear_css_refs") The former added a field to cgroup_subsys and the latter removed one from it. They happen to be colocated causing the conflict. Keeping what's added and removing what's removed resolves the conflict. Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c256
1 files changed, 61 insertions, 195 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b7a0171..e3045ad 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -171,8 +171,8 @@ struct css_id {
* The css to which this ID points. This pointer is set to valid value
* after cgroup is populated. If cgroup is removed, this will be NULL.
* This pointer is expected to be RCU-safe because destroy()
- * is called after synchronize_rcu(). But for safe use, css_is_removed()
- * css_tryget() should be used for avoiding race.
+ * is called after synchronize_rcu(). But for safe use, css_tryget()
+ * should be used for avoiding race.
*/
struct cgroup_subsys_state __rcu *css;
/*
@@ -854,30 +854,6 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
return inode;
}
-/*
- * Call subsys's pre_destroy handler.
- * This is called before css refcnt check.
- */
-static int cgroup_call_pre_destroy(struct cgroup *cgrp)
-{
- struct cgroup_subsys *ss;
- int ret = 0;
-
- for_each_subsys(cgrp->root, ss) {
- if (!ss->pre_destroy)
- continue;
-
- ret = ss->pre_destroy(cgrp);
- if (ret) {
- /* ->pre_destroy() failure is being deprecated */
- WARN_ON_ONCE(!ss->__DEPRECATED_clear_css_refs);
- break;
- }
- }
-
- return ret;
-}
-
static void cgroup_diput(struct dentry *dentry, struct inode *inode)
{
/* is dentry a directory ? if so, kfree() associated cgroup */
@@ -1015,33 +991,6 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
}
/*
- * A queue for waiters to do rmdir() cgroup. A tasks will sleep when
- * cgroup->count == 0 && list_empty(&cgroup->children) && subsys has some
- * reference to css->refcnt. In general, this refcnt is expected to goes down
- * to zero, soon.
- *
- * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
- */
-static DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
-
-static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
-{
- if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
- wake_up_all(&cgroup_rmdir_waitq);
-}
-
-void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
-{
- css_get(css);
-}
-
-void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
-{
- cgroup_wakeup_rmdir_waiter(css->cgroup);
- css_put(css);
-}
-
-/*
* Call with cgroup_mutex held. Drops reference counts on modules, including
* any duplicate ones that parse_cgroupfs_options took. If this function
* returns an error, no reference counts are touched.
@@ -2026,12 +1975,6 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
}
synchronize_rcu();
-
- /*
- * wake up rmdir() waiter. the rmdir should fail since the cgroup
- * is no longer empty.
- */
- cgroup_wakeup_rmdir_waiter(cgrp);
out:
if (retval) {
for_each_subsys(root, ss) {
@@ -2201,7 +2144,6 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* step 5: success! and cleanup
*/
synchronize_rcu();
- cgroup_wakeup_rmdir_waiter(cgrp);
retval = 0;
out_put_css_set_refs:
if (retval) {
@@ -4023,14 +3965,12 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
cgrp->subsys[ss->subsys_id] = css;
/*
- * If !clear_css_refs, css holds an extra ref to @cgrp->dentry
- * which is put on the last css_put(). dput() requires process
- * context, which css_put() may be called without. @css->dput_work
- * will be used to invoke dput() asynchronously from css_put().
+ * css holds an extra ref to @cgrp->dentry which is put on the last
+ * css_put(). dput() requires process context, which css_put() may
+ * be called without. @css->dput_work will be used to invoke
+ * dput() asynchronously from css_put().
*/
INIT_WORK(&css->dput_work, css_dput_fn);
- if (ss->__DEPRECATED_clear_css_refs)
- set_bit(CSS_CLEAR_CSS_REFS, &css->flags);
}
/*
@@ -4054,6 +3994,18 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (!cgrp)
return -ENOMEM;
+ /*
+ * Only live parents can have children. Note that the liveliness
+ * check isn't strictly necessary because cgroup_mkdir() and
+ * cgroup_rmdir() are fully synchronized by i_mutex; however, do it
+ * anyway so that locking is contained inside cgroup proper and we
+ * don't get nasty surprises if we ever grow another caller.
+ */
+ if (!cgroup_lock_live_group(parent)) {
+ err = -ENODEV;
+ goto err_free;
+ }
+
/* Grab a reference on the superblock so the hierarchy doesn't
* get deleted on unmount if there are child cgroups. This
* can be done outside cgroup_mutex, since the sb can't
@@ -4061,8 +4013,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
* fs */
atomic_inc(&sb->s_active);
- mutex_lock(&cgroup_mutex);
-
init_cgroup_housekeeping(cgrp);
cgrp->parent = parent;
@@ -4110,10 +4060,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (err < 0)
goto err_remove;
- /* If !clear_css_refs, each css holds a ref to the cgroup's dentry */
+ /* each css holds a ref to the cgroup's dentry */
for_each_subsys(root, ss)
- if (!ss->__DEPRECATED_clear_css_refs)
- dget(dentry);
+ dget(dentry);
/* The cgroup directory was pre-locked for us */
BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
@@ -4144,7 +4093,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
/* Release the reference count that we took on the superblock */
deactivate_super(sb);
-
+err_free:
kfree(cgrp);
return err;
}
@@ -4198,71 +4147,6 @@ static int cgroup_has_css_refs(struct cgroup *cgrp)
return 0;
}
-/*
- * Atomically mark all (or else none) of the cgroup's CSS objects as
- * CSS_REMOVED. Return true on success, or false if the cgroup has
- * busy subsystems. Call with cgroup_mutex held
- *
- * Depending on whether a subsys has __DEPRECATED_clear_css_refs set or
- * not, cgroup removal behaves differently.
- *
- * If clear is set, css refcnt for the subsystem should be zero before
- * cgroup removal can be committed. This is implemented by
- * CGRP_WAIT_ON_RMDIR and retry logic around ->pre_destroy(), which may be
- * called multiple times until all css refcnts reach zero and is allowed to
- * veto removal on any invocation. This behavior is deprecated and will be
- * removed as soon as the existing user (memcg) is updated.
- *
- * If clear is not set, each css holds an extra reference to the cgroup's
- * dentry and cgroup removal proceeds regardless of css refs.
- * ->pre_destroy() will be called at least once and is not allowed to fail.
- * On the last put of each css, whenever that may be, the extra dentry ref
- * is put so that dentry destruction happens only after all css's are
- * released.
- */
-static int cgroup_clear_css_refs(struct cgroup *cgrp)
-{
- struct cgroup_subsys *ss;
- unsigned long flags;
- bool failed = false;
-
- local_irq_save(flags);
-
- /*
- * Block new css_tryget() by deactivating refcnt. If all refcnts
- * for subsystems w/ clear_css_refs set were 1 at the moment of
- * deactivation, we succeeded.
- */
- for_each_subsys(cgrp->root, ss) {
- struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
-
- WARN_ON(atomic_read(&css->refcnt) < 0);
- atomic_add(CSS_DEACT_BIAS, &css->refcnt);
-
- if (ss->__DEPRECATED_clear_css_refs)
- failed |= css_refcnt(css) != 1;
- }
-
- /*
- * If succeeded, set REMOVED and put all the base refs; otherwise,
- * restore refcnts to positive values. Either way, all in-progress
- * css_tryget() will be released.
- */
- for_each_subsys(cgrp->root, ss) {
- struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
-
- if (!failed) {
- set_bit(CSS_REMOVED, &css->flags);
- css_put(css);
- } else {
- atomic_sub(CSS_DEACT_BIAS, &css->refcnt);
- }
- }
-
- local_irq_restore(flags);
- return !failed;
-}
-
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
struct cgroup *cgrp = dentry->d_fsdata;
@@ -4270,70 +4154,52 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
struct cgroup *parent;
DEFINE_WAIT(wait);
struct cgroup_event *event, *tmp;
- int ret;
+ struct cgroup_subsys *ss;
/* the vfs holds both inode->i_mutex already */
-again:
mutex_lock(&cgroup_mutex);
- if (atomic_read(&cgrp->count) != 0) {
- mutex_unlock(&cgroup_mutex);
- return -EBUSY;
- }
- if (!list_empty(&cgrp->children)) {
+ parent = cgrp->parent;
+ if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
- mutex_unlock(&cgroup_mutex);
/*
- * In general, subsystem has no css->refcnt after pre_destroy(). But
- * in racy cases, subsystem may have to get css->refcnt after
- * pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
- * make rmdir return -EBUSY too often. To avoid that, we use waitqueue
- * for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
- * and subsystem's reference count handling. Please see css_get/put
- * and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
+ * Block new css_tryget() by deactivating refcnt and mark @cgrp
+ * removed. This makes future css_tryget() and child creation
+ * attempts fail thus maintaining the removal conditions verified
+ * above.
*/
- set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+ for_each_subsys(cgrp->root, ss) {
+ struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
- /*
- * Call pre_destroy handlers of subsys. Notify subsystems
- * that rmdir() request comes.
- */
- ret = cgroup_call_pre_destroy(cgrp);
- if (ret) {
- clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
- return ret;
+ WARN_ON(atomic_read(&css->refcnt) < 0);
+ atomic_add(CSS_DEACT_BIAS, &css->refcnt);
}
+ set_bit(CGRP_REMOVED, &cgrp->flags);
+ /*
+ * Tell subsystems to initate destruction. pre_destroy() should be
+ * called with cgroup_mutex unlocked. See 3fa59dfbc3 ("cgroup: fix
+ * potential deadlock in pre_destroy") for details.
+ */
+ mutex_unlock(&cgroup_mutex);
+ for_each_subsys(cgrp->root, ss)
+ if (ss->pre_destroy)
+ ss->pre_destroy(cgrp);
mutex_lock(&cgroup_mutex);
- parent = cgrp->parent;
- if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
- clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
- mutex_unlock(&cgroup_mutex);
- return -EBUSY;
- }
- prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
- if (!cgroup_clear_css_refs(cgrp)) {
- mutex_unlock(&cgroup_mutex);
- /*
- * Because someone may call cgroup_wakeup_rmdir_waiter() before
- * prepare_to_wait(), we need to check this flag.
- */
- if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
- schedule();
- finish_wait(&cgroup_rmdir_waitq, &wait);
- clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
- if (signal_pending(current))
- return -EINTR;
- goto again;
- }
- /* NO css_tryget() can success after here. */
- finish_wait(&cgroup_rmdir_waitq, &wait);
- clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+
+ /*
+ * Put all the base refs. Each css holds an extra reference to the
+ * cgroup's dentry and cgroup removal proceeds regardless of css
+ * refs. On the last put of each css, whenever that may be, the
+ * extra dentry ref is put so that dentry destruction happens only
+ * after all css's are released.
+ */
+ for_each_subsys(cgrp->root, ss)
+ css_put(cgrp->subsys[ss->subsys_id]);
raw_spin_lock(&release_list_lock);
- set_bit(CGRP_REMOVED, &cgrp->flags);
if (!list_empty(&cgrp->release_list))
list_del_init(&cgrp->release_list);
raw_spin_unlock(&release_list_lock);
@@ -5041,15 +4907,17 @@ static void check_for_release(struct cgroup *cgrp)
/* Caller must verify that the css is not for root cgroup */
bool __css_tryget(struct cgroup_subsys_state *css)
{
- do {
- int v = css_refcnt(css);
+ while (true) {
+ int t, v;
- if (atomic_cmpxchg(&css->refcnt, v, v + 1) == v)
+ v = css_refcnt(css);
+ t = atomic_cmpxchg(&css->refcnt, v, v + 1);
+ if (likely(t == v))
return true;
+ else if (t < 0)
+ return false;
cpu_relax();
- } while (!test_bit(CSS_REMOVED, &css->flags));
-
- return false;
+ }
}
EXPORT_SYMBOL_GPL(__css_tryget);
@@ -5068,11 +4936,9 @@ void __css_put(struct cgroup_subsys_state *css)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
- cgroup_wakeup_rmdir_waiter(cgrp);
break;
case 0:
- if (!test_bit(CSS_CLEAR_CSS_REFS, &css->flags))
- schedule_work(&css->dput_work);
+ schedule_work(&css->dput_work);
break;
}
rcu_read_unlock();
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