Add a new macro for_each_subsys_which that allows all enabled cgroup
subsystems to be filtered by a bitmask, such that mask & (1 << ssid)
determines if the subsystem is to be processed in the loop body (where
ssid is the unique id of the subsystem).
Also replace the need_forkexit_callback with two separate bitmasks for
each callback to make (ss->{fork,exit}) checks unnecessary.
Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx>
---
include/linux/cgroup-defs.h | 2 ++
kernel/cgroup.c | 54 ++++++++++++++++++++++++++++-----------------
2 files changed, 36 insertions(+), 20 deletions(-)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 26d1cea..c5588c4 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -490,6 +490,8 @@ static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
#else /* CONFIG_CGROUPS */
+#define CGROUP_SUBSYS_COUNT 0
+
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {}
static inline void cgroup_threadgroup_change_end(struct task_struct *tsk) {}
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0fd5227..5734717 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -178,12 +178,13 @@ static DEFINE_IDR(cgroup_hierarchy_idr);
*/
static u64 css_serial_nr_next = 1;
-/* This flag indicates whether tasks in the fork and exit paths should
- * check for fork/exit handlers to call. This avoids us having to do
- * extra work in the fork/exit path if none of the subsystems need to
- * be called.
+/*
+ * These bitmask flags indicate whether tasks in the fork and exit paths have
+ * fork/exit handlers to call. This avoids us having to do extra work in the
+ * fork/exit path to check which subsystems have fork/exit callbacks.
*/
-static int need_forkexit_callback __read_mostly;
+static unsigned long have_fork_callback __read_mostly;
+static unsigned long have_exit_callback __read_mostly;
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@@ -412,6 +413,25 @@ static int notify_on_release(const struct cgroup *cgrp)
for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \
(((ss) = cgroup_subsys[ssid]) || true); (ssid)++)
+
+/**
+ * for_each_subsys_which - filter for_each_subsys with a bitmask
+ * @ss: the iteration cursor
+ * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end
+ * @ss_maskp: a pointer to the bitmask
+ *
+ * The block will only run for cases where the ssid-th bit (1 << ssid) of
+ * mask is set to 1.
+ */
+#define for_each_subsys_which(ss, ssid, ss_maskp) \
+ if (!CGROUP_SUBSYS_COUNT) \
+ ; \
+ else \
+ for_each_set_bit(ssid, ss_maskp, CGROUP_SUBSYS_COUNT) \
+ if (((ss) = cgroup_subsys[ssid]) && false) \
+ break; \
+ else
+
/* iterate across the hierarchies */
#define for_each_root(root) \
list_for_each_entry((root), &cgroup_roots, root_list)
@@ -4914,7 +4934,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
* init_css_set is in the subsystem's root cgroup. */
init_css_set.subsys[ss->id] = css;
- need_forkexit_callback |= ss->fork || ss->exit;
+ have_fork_callback |= (bool)ss->fork << ss->id;
+ have_exit_callback |= (bool)ss->exit << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@@ -5225,11 +5246,8 @@ void cgroup_post_fork(struct task_struct *child)
* css_set; otherwise, @child might change state between ->fork()
* and addition to css_set.
*/
- if (need_forkexit_callback) {
- for_each_subsys(ss, i)
- if (ss->fork)
- ss->fork(child);
- }
+ for_each_subsys_which(ss, i, &have_fork_callback)
+ ss->fork(child);
}
/**
@@ -5273,16 +5291,12 @@ void cgroup_exit(struct task_struct *tsk)
cset = task_css_set(tsk);
RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
- if (need_forkexit_callback) {
- /* see cgroup_post_fork() for details */
- for_each_subsys(ss, i) {
- if (ss->exit) {
- struct cgroup_subsys_state *old_css = cset->subsys[i];
- struct cgroup_subsys_state *css = task_css(tsk, i);
+ /* see cgroup_post_fork() for details */
+ for_each_subsys_which(ss, i, &have_exit_callback) {
+ struct cgroup_subsys_state *old_css = cset->subsys[i];
+ struct cgroup_subsys_state *css = task_css(tsk, i);
- ss->exit(css, old_css, tsk);
- }
- }
+ ss->exit(css, old_css, tsk);
}
if (put_cset)
--
2.4.2
--
To unsubscribe from this list: send the line "unsubscribe cgroups" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
