The patch titled
cgroup: fix potential deadlock in pre_destroy
has been added to the -mm tree. Its filename is
cgroup-fix-potential-deadlock-in-pre_destroy-v2.patch
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Subject: cgroup: fix potential deadlock in pre_destroy
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
As Balbir pointed out, memcg's pre_destroy handler has potential deadlock.
It has following lock sequence.
cgroup_mutex (cgroup_rmdir)
-> pre_destroy -> mem_cgroup_pre_destroy-> force_empty
-> cpu_hotplug.lock. (lru_add_drain_all->
schedule_work->
get_online_cpus)
But, cpuset has following.
cpu_hotplug.lock (call notifier)
-> cgroup_mutex. (within notifier)
Then, this lock sequence should be fixed.
Considering how pre_destroy works, it's not necessary to holding
cgroup_mutex() while calling it.
As a side effect, we don't have to wait at this mutex while memcg's
force_empty works.(it can be long when there are tons of pages.)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff -puN kernel/cgroup.c~cgroup-fix-potential-deadlock-in-pre_destroy-v2 kernel/cgroup.c
--- a/kernel/cgroup.c~cgroup-fix-potential-deadlock-in-pre_destroy-v2
+++ a/kernel/cgroup.c
@@ -2472,10 +2472,7 @@ static int cgroup_rmdir(struct inode *un
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
-
- parent = cgrp->parent;
- root = cgrp->root;
- sb = root->sb;
+ mutex_unlock(&cgroup_mutex);
/*
* Call pre_destroy handlers of subsys. Notify subsystems
@@ -2483,7 +2480,14 @@ static int cgroup_rmdir(struct inode *un
*/
cgroup_call_pre_destroy(cgrp);
- if (cgroup_has_css_refs(cgrp)) {
+ mutex_lock(&cgroup_mutex);
+ parent = cgrp->parent;
+ root = cgrp->root;
+ sb = root->sb;
+
+ if (atomic_read(&cgrp->count)
+ || !list_empty(&cgrp->children)
+ || cgroup_has_css_refs(cgrp)) {
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
_
Patches currently in -mm which might be from kamezawa.hiroyu@xxxxxxxxxxxxxx are
origin.patch
cgroup-fix-potential-deadlock-in-pre_destroy-v2.patch
cgroups-make-cgroup-config-a-submenu.patch
memcg-introduce-charge-commit-cancel-style-of-functions.patch
memcg-introduce-charge-commit-cancel-style-of-functions-fix.patch
memcg-fix-gfp_mask-of-callers-of-charge.patch
memcg-simple-migration-handling.patch
memcg-do-not-recalculate-section-unnecessarily-in-init_section_page_cgroup.patch
memcg-move-all-acccounts-to-parent-at-rmdir.patch
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