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Message-Id: <1351251453-6140-5-git-send-email-mhocko@suse.cz>
Date: Fri, 26 Oct 2012 13:37:31 +0200
From: Michal Hocko <mhocko@...e.cz>
To: linux-mm@...ck.org
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
Johannes Weiner <hannes@...xchg.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Balbir Singh <bsingharora@...il.com>,
Glauber Costa <glommer@...allels.com>
Subject: [PATCH v3 4/6] cgroups: forbid pre_destroy callback to fail
Now that mem_cgroup_pre_destroy callback doesn't fail (other than a race
with a task attach resp. child group appears) finally we can safely move
on and forbit all the callbacks to fail.
The last missing piece is moving cgroup_call_pre_destroy after
cgroup_clear_css_refs so that css_tryget fails so no new charges for the
memcg can happen.
We cannot, however, move cgroup_call_pre_destroy right after because we
cannot call mem_cgroup_pre_destroy with the cgroup_lock held (see
3fa59dfb cgroup: fix potential deadlock in pre_destroy) so we have to
move it after the lock is released.
Changes since v1
- Li Zefan pointed out that mem_cgroup_pre_destroy cannot be called with
cgroup_lock held
Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
kernel/cgroup.c | 30 +++++++++---------------------
1 file changed, 9 insertions(+), 21 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7981850..e9e2287b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -855,7 +855,7 @@ static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
* Call subsys's pre_destroy handler.
* This is called before css refcnt check.
*/
-static int cgroup_call_pre_destroy(struct cgroup *cgrp)
+static void cgroup_call_pre_destroy(struct cgroup *cgrp)
{
struct cgroup_subsys *ss;
int ret = 0;
@@ -864,15 +864,8 @@ static int cgroup_call_pre_destroy(struct cgroup *cgrp)
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;
- }
+ BUG_ON(ss->pre_destroy(cgrp));
}
-
- return ret;
}
static void cgroup_diput(struct dentry *dentry, struct inode *inode)
@@ -4151,7 +4144,6 @@ again:
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
- mutex_unlock(&cgroup_mutex);
/*
* In general, subsystem has no css->refcnt after pre_destroy(). But
@@ -4164,17 +4156,6 @@ again:
*/
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) {
- 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);
@@ -4196,6 +4177,7 @@ again:
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);
@@ -4234,6 +4216,12 @@ again:
spin_unlock(&cgrp->event_list_lock);
mutex_unlock(&cgroup_mutex);
+
+ /*
+ * Call pre_destroy handlers of subsys. Notify subsystems
+ * that rmdir() request comes.
+ */
+ cgroup_call_pre_destroy(cgrp);
return 0;
}
--
1.7.10.4
--
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