The patch titled
cgroup avoid permanent sleep at rmdir
has been removed from the -mm tree. Its filename was
cgroup-avoid-permanent-sleep-at-rmdir-v7.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: cgroup avoid permanent sleep at rmdir
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
After commit ec64f51545fffbc4cb968f0cea56341a4b07e85a ("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@xxxxxxxxxxxxxxxxx>
Reported-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Reviewed-by: Paul Menage <menage@xxxxxxxxxx>
Acked-by: Balbir Sigh <balbir@xxxxxxxxxxxxxxxxxx>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 17 ++++++++++++
kernel/cgroup.c | 55 ++++++++++++++++++++++++++-------------
mm/memcontrol.c | 23 ++++++++++++++--
3 files changed, 75 insertions(+), 20 deletions(-)
diff -puN include/linux/cgroup.h~cgroup-avoid-permanent-sleep-at-rmdir-v7 include/linux/cgroup.h
--- a/include/linux/cgroup.h~cgroup-avoid-permanent-sleep-at-rmdir-v7
+++ a/include/linux/cgroup.h
@@ -363,6 +363,23 @@ int cgroup_task_count(const struct cgrou
int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
/*
+ * When the subsys has to access css and may add permanent refcnt to css,
+ * it should take care of racy conditions with rmdir(). Following set of
+ * functions, is for stop/restart rmdir if necessary.
+ * Because these will call css_get/put, "css" should be alive css.
+ *
+ * cgroup_exclude_rmdir();
+ * ...do some jobs which may access arbitrary empty cgroup
+ * cgroup_release_and_wakeup_rmdir();
+ *
+ * When someone removes a cgroup while cgroup_exclude_rmdir() holds it,
+ * it sleeps and cgroup_release_and_wakeup_rmdir() will wake him up.
+ */
+
+void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
+void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);
+
+/*
* Control Group subsystem type.
* See Documentation/cgroups/cgroups.txt for details
*/
diff -puN kernel/cgroup.c~cgroup-avoid-permanent-sleep-at-rmdir-v7 kernel/cgroup.c
--- a/kernel/cgroup.c~cgroup-avoid-permanent-sleep-at-rmdir-v7
+++ a/kernel/cgroup.c
@@ -735,16 +735,28 @@ static void cgroup_d_remove_dir(struct d
* reference to css->refcnt. In general, this refcnt is expected to goes down
* to zero, soon.
*
- * CGRP_WAIT_ON_RMDIR flag is modified under cgroup's inode->i_mutex;
+ * CGRP_WAIT_ON_RMDIR flag is set under cgroup's inode->i_mutex;
*/
DECLARE_WAIT_QUEUE_HEAD(cgroup_rmdir_waitq);
-static void cgroup_wakeup_rmdir_waiters(const struct cgroup *cgrp)
+static void cgroup_wakeup_rmdir_waiter(struct cgroup *cgrp)
{
- if (unlikely(test_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags)))
+ 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);
+}
+
+
static int rebind_subsystems(struct cgroupfs_root *root,
unsigned long final_bits)
{
@@ -1359,7 +1371,7 @@ int cgroup_attach_task(struct cgroup *cg
* wake up rmdir() waiter. the rmdir should fail since the cgroup
* is no longer empty.
*/
- cgroup_wakeup_rmdir_waiters(cgrp);
+ cgroup_wakeup_rmdir_waiter(cgrp);
return 0;
}
@@ -2744,33 +2756,42 @@ again:
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.
+ */
+ set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
+
+ /*
* Call pre_destroy handlers of subsys. Notify subsystems
* that rmdir() request comes.
*/
ret = cgroup_call_pre_destroy(cgrp);
- if (ret)
+ if (ret) {
+ clear_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
return ret;
+ }
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;
}
- /*
- * css_put/get is provided for subsys to grab refcnt to css. In typical
- * case, subsystem has no reference after pre_destroy(). But, under
- * hierarchy management, some *temporal* refcnt can be hold.
- * To avoid returning -EBUSY to a user, waitqueue is used. If subsys
- * is really busy, it should return -EBUSY at pre_destroy(). wake_up
- * is called when css_put() is called and refcnt goes down to 0.
- */
- set_bit(CGRP_WAIT_ON_RMDIR, &cgrp->flags);
prepare_to_wait(&cgroup_rmdir_waitq, &wait, TASK_INTERRUPTIBLE);
-
if (!cgroup_clear_css_refs(cgrp)) {
mutex_unlock(&cgroup_mutex);
- schedule();
+ /*
+ * 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))
@@ -3342,7 +3363,7 @@ void __css_put(struct cgroup_subsys_stat
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
- cgroup_wakeup_rmdir_waiters(cgrp);
+ cgroup_wakeup_rmdir_waiter(cgrp);
}
rcu_read_unlock();
}
diff -puN mm/memcontrol.c~cgroup-avoid-permanent-sleep-at-rmdir-v7 mm/memcontrol.c
--- a/mm/memcontrol.c~cgroup-avoid-permanent-sleep-at-rmdir-v7
+++ a/mm/memcontrol.c
@@ -1207,6 +1207,12 @@ static int mem_cgroup_move_account(struc
ret = 0;
out:
unlock_page_cgroup(pc);
+ /*
+ * We charges against "to" which may not have any tasks. Then, "to"
+ * can be under rmdir(). But in current implementation, caller of
+ * this function is just force_empty() and it's garanteed that
+ * "to" is never removed. So, we don't check rmdir status here.
+ */
return ret;
}
@@ -1428,6 +1434,7 @@ __mem_cgroup_commit_charge_swapin(struct
return;
if (!ptr)
return;
+ cgroup_exclude_rmdir(&ptr->css);
pc = lookup_page_cgroup(page);
mem_cgroup_lru_del_before_commit_swapcache(page);
__mem_cgroup_commit_charge(ptr, pc, ctype);
@@ -1457,8 +1464,12 @@ __mem_cgroup_commit_charge_swapin(struct
}
rcu_read_unlock();
}
- /* add this page(page_cgroup) to the LRU we want. */
-
+ /*
+ * At swapin, we may charge account against cgroup which has no tasks.
+ * So, rmdir()->pre_destroy() can be called while we do this charge.
+ * In that case, we need to call pre_destroy() again. check it here.
+ */
+ cgroup_release_and_wakeup_rmdir(&ptr->css);
}
void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
@@ -1664,7 +1675,7 @@ void mem_cgroup_end_migration(struct mem
if (!mem)
return;
-
+ cgroup_exclude_rmdir(&mem->css);
/* at migration success, oldpage->mapping is NULL. */
if (oldpage->mapping) {
target = oldpage;
@@ -1704,6 +1715,12 @@ void mem_cgroup_end_migration(struct mem
*/
if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
mem_cgroup_uncharge_page(target);
+ /*
+ * At migration, we may charge account against cgroup which has no tasks
+ * So, rmdir()->pre_destroy() can be called while we do this charge.
+ * In that case, we need to call pre_destroy() again. check it here.
+ */
+ cgroup_release_and_wakeup_rmdir(&mem->css);
}
/*
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
origin.patch
mm-make-set_mempolicympol_interleav-n_high_memory-aware.patch
mm-make-set_mempolicympol_interleav-n_high_memory-aware-fix.patch
mm-clean-up-page_remove_rmap.patch
vmscan-throttle-direct-reclaim-when-too-many-pages-are-isolated-already.patch
mm-remove-__addsub_zone_page_state.patch
vmscan-dont-attempt-to-reclaim-anon-page-in-lumpy-reclaim-when-no-swap-space-is-avilable.patch
ksm-add-mmu_notifier-set_pte_at_notify.patch
ksm-first-tidy-up-madvise_vma.patch
ksm-define-madv_mergeable-and-madv_unmergeable.patch
ksm-the-mm-interface-to-ksm.patch
ksm-no-debug-in-page_dup_rmap.patch
ksm-identify-pageksm-pages.patch
ksm-kernel-samepage-merging.patch
ksm-prevent-mremap-move-poisoning.patch
ksm-change-copyright-message.patch
ksm-change-ksm-nice-level-to-be-5.patch
kcore-fix-proc-kcores-statst_size.patch
cgroups-support-named-cgroups-hierarchies.patch
cgroups-move-the-cgroup-debug-subsys-into-cgroupc-to-access-internal-state.patch
cgroups-add-a-back-pointer-from-struct-cg_cgroup_link-to-struct-cgroup.patch
cgroups-allow-cgroup-hierarchies-to-be-created-with-no-bound-subsystems.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup-fix.patch
memcg-remove-the-overhead-associated-with-the-root-cgroup-fix-2.patch
memcg-add-comments-explaining-memory-barriers.patch
memcg-add-comments-explaining-memory-barriers-checkpatch-fixes.patch
memory-controller-soft-limit-documentation-v9.patch
memory-controller-soft-limit-interface-v9.patch
memory-controller-soft-limit-organize-cgroups-v9.patch
memory-controller-soft-limit-refactor-reclaim-flags-v9.patch
memory-controller-soft-limit-reclaim-on-contention-v9.patch
memory-controller-soft-limit-reclaim-on-contention-v9-fix.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
