[PATCH 01/32] cgroup: Implement cgroup_show_cftypes()

Tejun Heo
2023-03-17T21:35:58Z

Implement cgroup_show_cftypes() which shows and hides all cgroup files
associated with the specified set of cgroup file types. CFTYPE_HIDDEN flag
is added so that files can be created hidden from the get-go.

cgroup_show_cftypes() can be used whether the cftypes are added or not. It
also combines with cgroup_show_file() so that a given file is visible iff
both its cftype and cfile are visible.

This will be used by a new sched_class to selectively show and hide CPU
controller interface files depending on whether they're supported.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Acked-by: Josh Don <joshdon@google.com>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Barret Rhoden <brho@google.com>
---
include/linux/cgroup-defs.h | 8 +++
include/linux/cgroup.h | 1 +
kernel/cgroup/cgroup.c | 97 ++++++++++++++++++++++++++++++++++---
3 files changed, 99 insertions(+), 7 deletions(-)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 8a0d5466c7be..8af1e7d487cb 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -127,12 +127,18 @@ enum {
CFTYPE_WORLD_WRITABLE = (1 << 4), /* (DON'T USE FOR NEW FILES) S_IWUGO */
CFTYPE_DEBUG = (1 << 5), /* create when cgroup_debug */

+ CFTYPE_HIDDEN = (1 << 6), /* file type hidden, see cgroup_show_cftypes() */
+
/* internal flags, do not use outside cgroup core proper */
__CFTYPE_ONLY_ON_DFL = (1 << 16), /* only on default hierarchy */
__CFTYPE_NOT_ON_DFL = (1 << 17), /* not on default hierarchy */
__CFTYPE_ADDED = (1 << 18),
};

+enum cfile_flags {
+ CFILE_HIDDEN = (1 << 0), /* file instance hidden */
+};
+
/*
* cgroup_file is the handle for a file instance created in a cgroup which
* is used, for example, to generate file changed notifications. This can
@@ -140,7 +146,9 @@ enum {
*/
struct cgroup_file {
/* do not access any fields from outside cgroup core */
+ struct cftype *cft;
struct kernfs_node *kn;
+ unsigned int flags;
unsigned long notified_at;
struct timer_list notify_timer;
};
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 3410aecffdb4..a8c6982c2c24 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -115,6 +115,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_rm_cftypes(struct cftype *cfts);
+void cgroup_show_cftype(struct cftype *cft, bool show);
void cgroup_file_notify(struct cgroup_file *cfile);
void cgroup_file_show(struct cgroup_file *cfile, bool show);

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8a5294f4ce72..f762bfb78f4a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4206,10 +4206,13 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
return ret;
}

+ kernfs_show(kn, !(cft->flags & CFTYPE_HIDDEN));
+
if (cft->file_offset) {
struct cgroup_file *cfile = (void *)css + cft->file_offset;

timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
+ cfile->cft = cft;

spin_lock_irq(&cgroup_file_kn_lock);
cfile->kn = kn;
@@ -4488,6 +4491,24 @@ void cgroup_file_notify(struct cgroup_file *cfile)
spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
}

+static struct kernfs_node *cfile_kn_get(struct cgroup_file *cfile)
+{
+ struct kernfs_node *kn;
+
+ spin_lock_irq(&cgroup_file_kn_lock);
+ kn = cfile->kn;
+ kernfs_get(kn);
+ spin_unlock_irq(&cgroup_file_kn_lock);
+
+ return kn;
+}
+
+static bool cfile_visible(struct cgroup_file *cfile)
+{
+ return !(cfile->cft->flags & CFTYPE_HIDDEN) &&
+ !(cfile->flags & CFILE_HIDDEN);
+}
+
/**
* cgroup_file_show - show or hide a hidden cgroup file
* @cfile: target cgroup_file obtained by setting cftype->file_offset
@@ -4497,15 +4518,20 @@ void cgroup_file_show(struct cgroup_file *cfile, bool show)
{
struct kernfs_node *kn;

- spin_lock_irq(&cgroup_file_kn_lock);
- kn = cfile->kn;
- kernfs_get(kn);
- spin_unlock_irq(&cgroup_file_kn_lock);
+ mutex_lock(&cgroup_mutex);

- if (kn)
- kernfs_show(kn, show);
+ if (show)
+ cfile->flags &= ~CFILE_HIDDEN;
+ else
+ cfile->flags |= CFILE_HIDDEN;

- kernfs_put(kn);
+ kn = cfile_kn_get(cfile);
+ if (kn) {
+ kernfs_show(kn, cfile_visible(cfile));
+ kernfs_put(kn);
+ }
+
+ mutex_unlock(&cgroup_mutex);
}

/**
@@ -5519,6 +5545,63 @@ static void offline_css(struct cgroup_subsys_state *css)
wake_up_all(&css->cgroup->offline_waitq);
}

+/**
+ * cgroup_show_cftype - show or hide a cgroup file type
+ * @cft: cftype to show or hide
+ * @show: whether to show or hide
+ *
+ * Sets %CFTYPE_HIDDEN and shows/hides the matching files according to @show.
+ * @cft may or may not be added at the time of this call. After hiding, it's
+ * guaranteed that there are no in-flight operations on the hidden files.
+ */
+void cgroup_show_cftype(struct cftype *cft, bool show)
+{
+ struct cgroup_subsys *ss = cft->ss;
+ struct cgroup *root = ss ? &ss->root->cgrp : &cgrp_dfl_root.cgrp;
+ struct cgroup_subsys_state *css;
+
+ mutex_lock(&cgroup_mutex);
+
+ if (show)
+ cft->flags &= ~CFTYPE_HIDDEN;
+ else
+ cft->flags |= CFTYPE_HIDDEN;
+
+ if (!(cft->flags & __CFTYPE_ADDED))
+ goto out_unlock;
+
+ css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
+ struct cgroup *cgrp = css->cgroup;
+ struct kernfs_node *kn;
+
+ if (!(css->flags & CSS_VISIBLE))
+ continue;
+
+ if (cft->file_offset) {
+ struct cgroup_file *cfile =
+ (void *)css + cft->file_offset;
+
+ kn = cfile_kn_get(cfile);
+ if (kn) {
+ kernfs_show(kn, cfile_visible(cfile));
+ kernfs_put(kn);
+ }
+ } else {
+ char buf[CGROUP_FILE_NAME_MAX];
+
+ kn = kernfs_find_and_get(cgrp->kn,
+ cgroup_file_name(cgrp, cft, buf));
+ if (kn) {
+ kernfs_show(kn, show);
+ kernfs_put(kn);
+ }
+ }
+ }
+
+out_unlock:
+ mutex_unlock(&cgroup_mutex);
+}
+
/**
* css_create - create a cgroup_subsys_state
* @cgrp: the cgroup new css will be associated with
--
2.39.2