cgroup avoid permanent sleep at rmdir
After commit ec64f51545
("cgroup: fix
frequent -EBUSY at rmdir"), cgroup's rmdir (especially against memcg)
doesn't return -EBUSY by temporary ref counts. That commit expects all
refs after pre_destroy() is temporary but...it wasn't. Then, rmdir can
wait permanently. This patch tries to fix that and change followings.
- set CGRP_WAIT_ON_RMDIR flag before pre_destroy().
- clear CGRP_WAIT_ON_RMDIR flag when the subsys finds racy case.
if there are sleeping ones, wakes them up.
- rmdir() sleeps only when CGRP_WAIT_ON_RMDIR flag is set.
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reported-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: Paul Menage <menage@google.com>
Acked-by: Balbir Sigh <balbir@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
f0d83679a8
commit
887032670d
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@ -362,6 +362,23 @@ int cgroup_task_count(const struct cgroup *cgrp);
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/* Return true if cgrp is a descendant of the task's cgroup */
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/* Return true if cgrp is a descendant of the task's cgroup */
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int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
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int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
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/*
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* When the subsys has to access css and may add permanent refcnt to css,
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* it should take care of racy conditions with rmdir(). Following set of
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* functions, is for stop/restart rmdir if necessary.
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* Because these will call css_get/put, "css" should be alive css.
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*
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* cgroup_exclude_rmdir();
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* ...do some jobs which may access arbitrary empty cgroup
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* cgroup_release_and_wakeup_rmdir();
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*
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* When someone removes a cgroup while cgroup_exclude_rmdir() holds it,
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* it sleeps and cgroup_release_and_wakeup_rmdir() will wake him up.
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*/
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void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
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void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);
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/*
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/*
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* Control Group subsystem type.
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* Control Group subsystem type.
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* See Documentation/cgroups/cgroups.txt for details
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* See Documentation/cgroups/cgroups.txt for details
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@ -735,16 +735,28 @@ static void cgroup_d_remove_dir(struct dentry *dentry)
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* reference to css->refcnt. In general, this refcnt is expected to goes down
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* reference to css->refcnt. In general, this refcnt is expected to goes down
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* to zero, soon.
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* to zero, soon.
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*
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*
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* CGRP_WAIT_ON_RMDIR flag is modified under cgroup's inode->i_mutex;
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* CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
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*/
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*/
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DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
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DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
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static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp)
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static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
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{
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{
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if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
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if (unlikely(test_and_clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
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wake_up_all(&cgroup_rmdir_waitq);
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wake_up_all(&cgroup_rmdir_waitq);
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}
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}
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void cgroup_exclude_rmdir(struct cgroup_subsys_state *css)
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{
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css_get(css);
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}
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void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
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{
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cgroup_wakeup_rmdir_waiter(css->cgroup);
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css_put(css);
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}
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static int rebind_subsystems(struct cgroupfs_root *root,
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static int rebind_subsystems(struct cgroupfs_root *root,
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unsigned long final_bits)
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unsigned long final_bits)
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{
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{
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@ -1359,7 +1371,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
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* wake up rmdir() waiter. the rmdir should fail since the cgroup
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* wake up rmdir() waiter. the rmdir should fail since the cgroup
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* is no longer empty.
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* is no longer empty.
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*/
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*/
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cgroup_wakeup_rmdir_waiters(cgrp);
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cgroup_wakeup_rmdir_waiter(cgrp);
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return 0;
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return 0;
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}
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}
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@ -2743,34 +2755,43 @@ again:
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}
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}
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mutex_unlock(&cgroup_mutex);
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mutex_unlock(&cgroup_mutex);
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/*
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* In general, subsystem has no css->refcnt after pre_destroy(). But
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* in racy cases, subsystem may have to get css->refcnt after
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* pre_destroy() and it makes rmdir return with -EBUSY. This sometimes
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* make rmdir return -EBUSY too often. To avoid that, we use waitqueue
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* for cgroup's rmdir. CGRP_WAIT_ON_RMDIR is for synchronizing rmdir
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* and subsystem's reference count handling. Please see css_get/put
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* and css_tryget() and cgroup_wakeup_rmdir_waiter() implementation.
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*/
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set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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/*
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/*
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* Call pre_destroy handlers of subsys. Notify subsystems
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* Call pre_destroy handlers of subsys. Notify subsystems
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* that rmdir() request comes.
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* that rmdir() request comes.
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*/
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*/
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ret = cgroup_call_pre_destroy(cgrp);
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ret = cgroup_call_pre_destroy(cgrp);
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if (ret)
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if (ret) {
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clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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return ret;
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return ret;
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}
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mutex_lock(&cgroup_mutex);
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mutex_lock(&cgroup_mutex);
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parent = cgrp->parent;
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parent = cgrp->parent;
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if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
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if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) {
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clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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mutex_unlock(&cgroup_mutex);
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mutex_unlock(&cgroup_mutex);
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return -EBUSY;
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return -EBUSY;
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}
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}
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/*
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* css_put/get is provided for subsys to grab refcnt to css. In typical
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* case, subsystem has no reference after pre_destroy(). But, under
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* hierarchy management, some *temporal* refcnt can be hold.
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* To avoid returning -EBUSY to a user, waitqueue is used. If subsys
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* is really busy, it should return -EBUSY at pre_destroy(). wake_up
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* is called when css_put() is called and refcnt goes down to 0.
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*/
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set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
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prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
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if (!cgroup_clear_css_refs(cgrp)) {
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if (!cgroup_clear_css_refs(cgrp)) {
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mutex_unlock(&cgroup_mutex);
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mutex_unlock(&cgroup_mutex);
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schedule();
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/*
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* Because someone may call cgroup_wakeup_rmdir_waiter() before
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* prepare_to_wait(), we need to check this flag.
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*/
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if (test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags))
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schedule();
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finish_wait(&cgroup_rmdir_waitq, &wait);
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finish_wait(&cgroup_rmdir_waitq, &wait);
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clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
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if (signal_pending(current))
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if (signal_pending(current))
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@ -3342,7 +3363,7 @@ void __css_put(struct cgroup_subsys_state *css)
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set_bit(CGRP_RELEASABLE, &cgrp->flags);
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set_bit(CGRP_RELEASABLE, &cgrp->flags);
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check_for_release(cgrp);
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check_for_release(cgrp);
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}
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}
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cgroup_wakeup_rmdir_waiters(cgrp);
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cgroup_wakeup_rmdir_waiter(cgrp);
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}
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}
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rcu_read_unlock();
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rcu_read_unlock();
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}
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}
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@ -1207,6 +1207,12 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
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ret = 0;
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ret = 0;
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out:
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out:
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unlock_page_cgroup(pc);
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unlock_page_cgroup(pc);
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/*
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* We charges against "to" which may not have any tasks. Then, "to"
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* can be under rmdir(). But in current implementation, caller of
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* this function is just force_empty() and it's garanteed that
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* "to" is never removed. So, we don't check rmdir status here.
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*/
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return ret;
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return ret;
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}
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}
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@ -1428,6 +1434,7 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
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return;
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return;
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if (!ptr)
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if (!ptr)
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return;
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return;
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cgroup_exclude_rmdir(&ptr->css);
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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mem_cgroup_lru_del_before_commit_swapcache(page);
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mem_cgroup_lru_del_before_commit_swapcache(page);
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__mem_cgroup_commit_charge(ptr, pc, ctype);
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__mem_cgroup_commit_charge(ptr, pc, ctype);
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@ -1457,8 +1464,12 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
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}
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}
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rcu_read_unlock();
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rcu_read_unlock();
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}
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}
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/* add this page(page_cgroup) to the LRU we want. */
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/*
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* At swapin, we may charge account against cgroup which has no tasks.
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* So, rmdir()->pre_destroy() can be called while we do this charge.
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* In that case, we need to call pre_destroy() again. check it here.
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*/
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cgroup_release_and_wakeup_rmdir(&ptr->css);
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}
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}
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void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
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void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
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@ -1664,7 +1675,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
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if (!mem)
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if (!mem)
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return;
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return;
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cgroup_exclude_rmdir(&mem->css);
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/* at migration success, oldpage->mapping is NULL. */
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/* at migration success, oldpage->mapping is NULL. */
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if (oldpage->mapping) {
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if (oldpage->mapping) {
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target = oldpage;
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target = oldpage;
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@ -1704,6 +1715,12 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
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*/
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*/
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if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
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if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
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mem_cgroup_uncharge_page(target);
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mem_cgroup_uncharge_page(target);
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/*
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* At migration, we may charge account against cgroup which has no tasks
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* So, rmdir()->pre_destroy() can be called while we do this charge.
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* In that case, we need to call pre_destroy() again. check it here.
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*/
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cgroup_release_and_wakeup_rmdir(&mem->css);
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}
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}
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/*
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/*
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