cgroup: fix cftype->file_offset handling
6f60eade2433 ("cgroup: generalize obtaining the handles of and
notifying cgroup files") introduced cftype->file_offset so that the
handles for per-css file instances can be recorded. These handles
then can be used, for example, to generate file modified
notifications.
Unfortunately, it made the wrong assumption that files are created
once for a given css and removed on its destruction. Due to the
dependencies among subsystems, a css may be hidden from userland and
then later shown again. This is implemented by removing and
re-creating the affected files, so the associated kernfs_node for a
given cgroup file may change over time. This incorrect assumption led
to the corruption of css->files lists.
Reimplement cftype->file_offset handling so that cgroup_file->kn is
protected by a lock and updated as files are created and destroyed.
This also makes keeping them on per-cgroup list unnecessary.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: James Sedgwick <jsedgwick@fb.com>
Fixes: 6f60eade2433 ("cgroup: generalize obtaining the handles of and notifying cgroup files")
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Zefan Li <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f1603c1..b316deb 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -98,6 +98,12 @@
static DEFINE_SPINLOCK(cgroup_idr_lock);
/*
+ * Protects cgroup_file->kn for !self csses. It synchronizes notifications
+ * against file removal/re-creation across css hiding.
+ */
+static DEFINE_SPINLOCK(cgroup_file_kn_lock);
+
+/*
* Protects cgroup_subsys->release_agent_path. Modifying it also requires
* cgroup_mutex. Reading requires either cgroup_mutex or this spinlock.
*/
@@ -1393,6 +1399,16 @@
char name[CGROUP_FILE_NAME_MAX];
lockdep_assert_held(&cgroup_mutex);
+
+ if (cft->file_offset) {
+ struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss);
+ struct cgroup_file *cfile = (void *)css + cft->file_offset;
+
+ spin_lock_irq(&cgroup_file_kn_lock);
+ cfile->kn = NULL;
+ spin_unlock_irq(&cgroup_file_kn_lock);
+ }
+
kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
}
@@ -1856,7 +1872,6 @@
INIT_LIST_HEAD(&cgrp->self.sibling);
INIT_LIST_HEAD(&cgrp->self.children);
- INIT_LIST_HEAD(&cgrp->self.files);
INIT_LIST_HEAD(&cgrp->cset_links);
INIT_LIST_HEAD(&cgrp->pidlists);
mutex_init(&cgrp->pidlist_mutex);
@@ -3313,9 +3328,9 @@
if (cft->file_offset) {
struct cgroup_file *cfile = (void *)css + cft->file_offset;
- kernfs_get(kn);
+ spin_lock_irq(&cgroup_file_kn_lock);
cfile->kn = kn;
- list_add(&cfile->node, &css->files);
+ spin_unlock_irq(&cgroup_file_kn_lock);
}
return 0;
@@ -3553,6 +3568,22 @@
}
/**
+ * cgroup_file_notify - generate a file modified event for a cgroup_file
+ * @cfile: target cgroup_file
+ *
+ * @cfile must have been obtained by setting cftype->file_offset.
+ */
+void cgroup_file_notify(struct cgroup_file *cfile)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&cgroup_file_kn_lock, flags);
+ if (cfile->kn)
+ kernfs_notify(cfile->kn);
+ spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
+}
+
+/**
* cgroup_task_count - count the number of tasks in a cgroup.
* @cgrp: the cgroup in question
*
@@ -4613,13 +4644,9 @@
container_of(work, struct cgroup_subsys_state, destroy_work);
struct cgroup_subsys *ss = css->ss;
struct cgroup *cgrp = css->cgroup;
- struct cgroup_file *cfile;
percpu_ref_exit(&css->refcnt);
- list_for_each_entry(cfile, &css->files, node)
- kernfs_put(cfile->kn);
-
if (ss) {
/* css free path */
int id = css->id;
@@ -4724,7 +4751,6 @@
css->ss = ss;
INIT_LIST_HEAD(&css->sibling);
INIT_LIST_HEAD(&css->children);
- INIT_LIST_HEAD(&css->files);
css->serial_nr = css_serial_nr_next++;
if (cgroup_parent(cgrp)) {
