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cgroup: use cgroup_kn_lock_live() in other cgroup kernfs methods 

Make __cgroup_procs_write() and cgroup_release_agent_write() use
cgroup_kn_lock_live() and cgroup_kn_unlock() instead of
cgroup_lock_live_group().  This puts the operations under both
cgroup_tree_mutex and cgroup_mutex protection without circular
dependency from kernfs active protection.  Also, this means that
cgroup_mutex is no longer nested below kernfs active protection.
There is no longer any place where the two locks interact.

This leaves cgroup_lock_live_group() without any user.  Removed.

This will help simplifying cgroup locking.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-05-13 12:19:23 -04:00
parent a9746d8da7
commit e76ecaeef6
1 changed files with 12 additions and 27 deletions
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39
kernel/cgroup.c
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@ -386,23 +386,6 @@ static int notify_on_release(const struct cgroup *cgrp)
; \
else
/**
* cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
* @cgrp: the cgroup to be checked for liveness
*
* On success, returns true; the mutex should be later unlocked. On
* failure returns false with no lock held.
*/
static bool cgroup_lock_live_group(struct cgroup *cgrp)
{
mutex_lock(&cgroup_mutex);
if (cgroup_is_dead(cgrp)) {
mutex_unlock(&cgroup_mutex);
return false;
}
return true;
}
/* the list of cgroups eligible for automatic release. Protected by
* release_list_lock */
static LIST_HEAD(release_list);
@ -2306,14 +2289,15 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
{
struct task_struct *tsk;
const struct cred *cred = current_cred(), *tcred;
struct cgroup *cgrp = of_css(of)->cgroup;
struct cgroup *cgrp;
pid_t pid;
int ret;
if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
return -EINVAL;
if (!cgroup_lock_live_group(cgrp))
cgrp = cgroup_kn_lock_live(of->kn);
if (!cgrp)
return -ENODEV;
retry_find_task:
@ -2379,7 +2363,7 @@ retry_find_task:
put_task_struct(tsk);
out_unlock_cgroup:
mutex_unlock(&cgroup_mutex);
cgroup_kn_unlock(of->kn);
return ret ?: nbytes;
}
@ -2429,17 +2413,18 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of,
static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
struct cgroup *cgrp = of_css(of)->cgroup;
struct cgroup_root *root = cgrp->root;
struct cgroup *cgrp;
BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);
if (!cgroup_lock_live_group(cgrp))
BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
cgrp = cgroup_kn_lock_live(of->kn);
if (!cgrp)
return -ENODEV;
spin_lock(&release_agent_path_lock);
strlcpy(root->release_agent_path, strstrip(buf),
sizeof(root->release_agent_path));
strlcpy(cgrp->root->release_agent_path, strstrip(buf),
sizeof(cgrp->root->release_agent_path));
spin_unlock(&release_agent_path_lock);
mutex_unlock(&cgroup_mutex);
cgroup_kn_unlock(of->kn);
return nbytes;
}