After the recent changes, pidlist ref is held only between
cgroup_pidlist_start() and cgroup_pidlist_stop() during which
cgroup->pidlist_mutex is also held. IOW, the reference count is
redundant now. While in use, it's always one and pidlist_mutex is
held - holding the mutex has exactly the same protection.
This patch collapses destroy_dwork queueing into cgroup_pidlist_stop()
so that pidlist_mutex is not released inbetween and drops
pidlist->use_count.
This patch shouldn't introduce any behavior changes.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup.c | 28 +++++++---------------------
1 file changed, 7 insertions(+), 21 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8d2d9d4..5c8cf0b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3454,8 +3454,6 @@ struct cgroup_pidlist {
pid_t *list;
/* how many elements the above list has */
int length;
- /* how many files are using the current array */
- int use_count;
/* each of these stored in a list by its cgroup */
struct list_head links;
/* pointer to the cgroup we belong to, for list removal purposes */
@@ -3471,8 +3469,6 @@ struct cgroup_pidlist_open_file {
struct cgroup_pidlist *pidlist;
};
-static void cgroup_release_pid_array(struct cgroup_pidlist *l);
-
/*
* The following two functions "fix" the issue where there are more pids
* than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
@@ -3522,10 +3518,10 @@ static void cgroup_pidlist_destroy_work_fn(struct work_struct *work)
mutex_lock(&l->owner->pidlist_mutex);
/*
- * Destroy iff we didn't race with a new user or get queued again.
- * Queued state won't change as it can only be queued while locked.
+ * Destroy iff we didn't get queued again. The state won't change
+ * as destroy_dwork can only be queued while locked.
*/
- if (!l->use_count && !delayed_work_pending(dwork)) {
+ if (!delayed_work_pending(dwork)) {
list_del(&l->links);
pidlist_free(l->list);
put_pid_ns(l->key.ns);
@@ -3773,7 +3769,6 @@ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
return ERR_PTR(ret);
}
l = of->pidlist;
- l->use_count++;
if (pid) {
int end = l->length;
@@ -3802,9 +3797,11 @@ static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
struct cgroup_pidlist_open_file *of = s->private;
- mutex_unlock(&of->cgrp->pidlist_mutex);
if (of->pidlist)
- cgroup_release_pid_array(of->pidlist);
+ mod_delayed_work(cgroup_pidlist_destroy_wq,
+ &of->pidlist->destroy_dwork,
+ CGROUP_PIDLIST_DESTROY_DELAY);
+ mutex_unlock(&of->cgrp->pidlist_mutex);
}
static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
@@ -3842,17 +3839,6 @@ static const struct seq_operations cgroup_pidlist_seq_operations = {
.show = cgroup_pidlist_show,
};
-static void cgroup_release_pid_array(struct cgroup_pidlist *l)
-{
- mutex_lock(&l->owner->pidlist_mutex);
- BUG_ON(!l->use_count);
- /* if the last user, arm the destroy work */
- if (!--l->use_count)
- mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork,
- CGROUP_PIDLIST_DESTROY_DELAY);
- mutex_unlock(&l->owner->pidlist_mutex);
-}
-
static const struct file_operations cgroup_pidlist_operations = {
.read = seq_read,
.llseek = seq_lseek,
--
1.8.4.2
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