[PATCH 3/6] cgroup: introduce cgroup_taskset and use it in subsys->can_attach(), cancel_attach() and attach()

From: Tejun Heo
Date: Tue Aug 23 2011 - 18:21:12 EST

Currently, there's no way to pass multiple tasks to cgroup_subsys
methods necessitating the need for separate per-process and per-task
methods. This patch introduces cgroup_taskset which can be used to
pass multiple tasks and their associated cgroups to cgroup_subsys
methods.

Three methods - can_attach(), cancel_attach() and attach() - are
converted to use cgroup_taskset. This unifies passed parameters so
that all methods have access to all information. Conversions in this
patchset are identical and don't introduce any behavior change.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Paul Menage <paul@xxxxxxxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
---
Documentation/cgroups/cgroups.txt | 26 ++++++----
include/linux/cgroup.h | 28 +++++++++-
kernel/cgroup.c | 99 +++++++++++++++++++++++++++++++++----
kernel/cgroup_freezer.c | 2 +-
kernel/cpuset.c | 18 ++++---
mm/memcontrol.c | 16 +++---
security/device_cgroup.c | 7 ++-
7 files changed, 153 insertions(+), 43 deletions(-)

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index cd67e90..2eee7cf 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -594,16 +594,21 @@ rmdir() will fail with it. From this behavior, pre_destroy() can be
called multiple times against a cgroup.

int can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct task_struct *task)
+ struct cgroup_taskset *tset)
(cgroup_mutex held by caller)

-Called prior to moving a task into a cgroup; if the subsystem
-returns an error, this will abort the attach operation. If a NULL
-task is passed, then a successful result indicates that *any*
-unspecified task can be moved into the cgroup. Note that this isn't
+Called prior to moving one or more tasks into a cgroup; if the
+subsystem returns an error, this will abort the attach operation.
+@tset contains the tasks to be attached and is guaranteed to have at
+least one task in it. If there are multiple, it's guaranteed that all
+are from the same thread group, @tset contains all tasks from the
+group whether they're actually switching cgroup or not, and the first
+task is the leader. Each @tset entry also contains the task's old
+cgroup and tasks which aren't switching cgroup can be skipped easily
+using the cgroup_taskset_for_each() iterator. Note that this isn't
called on a fork. If this method returns 0 (success) then this should
-remain valid while the caller holds cgroup_mutex and it is ensured that either
-attach() or cancel_attach() will be called in future.
+remain valid while the caller holds cgroup_mutex and it is ensured
+that either attach() or cancel_attach() will be called in future.

int can_attach_task(struct cgroup *cgrp, struct task_struct *tsk);
(cgroup_mutex held by caller)
@@ -613,14 +618,14 @@ attached (possibly many when using cgroup_attach_proc). Called after
can_attach.

void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct task_struct *task, bool threadgroup)
+ struct cgroup_taskset *tset)
(cgroup_mutex held by caller)

Called when a task attach operation has failed after can_attach() has succeeded.
A subsystem whose can_attach() has some side-effects should provide this
function, so that the subsystem can implement a rollback. If not, not necessary.
This will be called only about subsystems whose can_attach() operation have
-succeeded.
+succeeded. The parameters are identical to can_attach().

void pre_attach(struct cgroup *cgrp);
(cgroup_mutex held by caller)
@@ -629,11 +634,12 @@ For any non-per-thread attachment work that needs to happen before
attach_task. Needed by cpuset.

void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct cgroup *old_cgrp, struct task_struct *task)
+ struct cgroup_taskset *tset)
(cgroup_mutex held by caller)

Called after the task has been attached to the cgroup, to allow any
post-attachment activity that requires memory allocations or blocking.
+The parameters are identical to can_attach().

void attach_task(struct cgroup *cgrp, struct task_struct *tsk);
(cgroup_mutex held by caller)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index da7e4bc..2470c8e 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -457,6 +457,28 @@ void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);

/*
+ * Control Group taskset, used to pass around set of tasks to cgroup_subsys
+ * methods.
+ */
+struct cgroup_taskset;
+struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset);
+struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset);
+struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset);
+int cgroup_taskset_size(struct cgroup_taskset *tset);
+
+/**
+ * cgroup_taskset_for_each - iterate cgroup_taskset
+ * @task: the loop cursor
+ * @skip_cgrp: skip if task's cgroup matches this, %NULL to iterate through all
+ * @tset: taskset to iterate
+ */
+#define cgroup_taskset_for_each(task, skip_cgrp, tset) \
+ for ((task) = cgroup_taskset_first((tset)); (task); \
+ (task) = cgroup_taskset_next((tset))) \
+ if (!(skip_cgrp) || \
+ cgroup_taskset_cur_cgroup((tset)) != (skip_cgrp))
+
+/*
* Control Group subsystem type.
* See Documentation/cgroups/cgroups.txt for details
*/
@@ -467,14 +489,14 @@ struct cgroup_subsys {
int (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
int (*can_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct task_struct *tsk);
+ struct cgroup_taskset *tset);
int (*can_attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
void (*cancel_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct task_struct *tsk);
+ struct cgroup_taskset *tset);
void (*pre_attach)(struct cgroup *cgrp);
void (*attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
- struct cgroup *old_cgrp, struct task_struct *tsk);
+ struct cgroup_taskset *tset);
void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
void (*exit)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup *old_cgrp, struct task_struct *task);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cf5f3e3..474674b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1739,11 +1739,85 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
}
EXPORT_SYMBOL_GPL(cgroup_path);

+/*
+ * Control Group taskset
+ */
struct task_and_cgroup {
struct task_struct *task;
struct cgroup *cgrp;
};

+struct cgroup_taskset {
+ struct task_and_cgroup single;
+ struct flex_array *tc_array;
+ int tc_array_len;
+ int idx;
+ struct cgroup *cur_cgrp;
+};
+
+/**
+ * cgroup_taskset_first - reset taskset and return the first task
+ * @tset: taskset of interest
+ *
+ * @tset iteration is initialized and the first task is returned.
+ */
+struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset)
+{
+ if (tset->tc_array) {
+ tset->idx = 0;
+ return cgroup_taskset_next(tset);
+ } else {
+ tset->cur_cgrp = tset->single.cgrp;
+ return tset->single.task;
+ }
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_first);
+
+/**
+ * cgroup_taskset_next - iterate to the next task in taskset
+ * @tset: taskset of interest
+ *
+ * Return the next task in @tset. Iteration must have been initialized
+ * with cgroup_taskset_first().
+ */
+struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset)
+{
+ struct task_and_cgroup *tc;
+
+ if (!tset->tc_array || tset->idx >= tset->tc_array_len)
+ return NULL;
+
+ tc = flex_array_get(tset->tc_array, tset->idx++);
+ tset->cur_cgrp = tc->cgrp;
+ return tc->task;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_next);
+
+/**
+ * cgroup_taskset_cur_cgroup - return the matching cgroup for the current task
+ * @tset: taskset of interest
+ *
+ * Return the cgroup for the current (last returned) task of @tset. This
+ * function must be preceded by either cgroup_taskset_first() or
+ * cgroup_taskset_next().
+ */
+struct cgroup *cgroup_taskset_cur_cgroup(struct cgroup_taskset *tset)
+{
+ return tset->cur_cgrp;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_cur_cgroup);
+
+/**
+ * cgroup_taskset_size - return the number of tasks in taskset
+ * @tset: taskset of interest
+ */
+int cgroup_taskset_size(struct cgroup_taskset *tset)
+{
+ return tset->tc_array ? tset->tc_array_len : 1;
+}
+EXPORT_SYMBOL_GPL(cgroup_taskset_size);
+
+
/*
* cgroup_task_migrate - move a task from one cgroup to another.
*
@@ -1828,15 +1902,19 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
struct cgroupfs_root *root = cgrp->root;
+ struct cgroup_taskset tset = { };

/* Nothing to do if the task is already in that cgroup */
oldcgrp = task_cgroup_from_root(tsk, root);
if (cgrp == oldcgrp)
return 0;

+ tset.single.task = tsk;
+ tset.single.cgrp = oldcgrp;
+
for_each_subsys(root, ss) {
if (ss->can_attach) {
- retval = ss->can_attach(ss, cgrp, tsk);
+ retval = ss->can_attach(ss, cgrp, &tset);
if (retval) {
/*
* Remember on which subsystem the can_attach()
@@ -1867,7 +1945,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
if (ss->attach_task)
ss->attach_task(cgrp, tsk);
if (ss->attach)
- ss->attach(ss, cgrp, oldcgrp, tsk);
+ ss->attach(ss, cgrp, &tset);
}

synchronize_rcu();
@@ -1889,7 +1967,7 @@ out:
*/
break;
if (ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, tsk);
+ ss->cancel_attach(ss, cgrp, &tset);
}
}
return retval;
@@ -2005,6 +2083,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
struct task_struct *tsk;
struct task_and_cgroup *tc;
struct flex_array *group;
+ struct cgroup_taskset tset = { };
/*
* we need to make sure we have css_sets for all the tasks we're
* going to move -before- we actually start moving them, so that in
@@ -2067,6 +2146,8 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
+ tset.tc_array = group;
+ tset.tc_array_len = group_size;
rcu_read_unlock();

/* methods shouldn't be called if no task is actually migrating */
@@ -2079,7 +2160,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
*/
for_each_subsys(root, ss) {
if (ss->can_attach) {
- retval = ss->can_attach(ss, cgrp, leader);
+ retval = ss->can_attach(ss, cgrp, &tset);
if (retval) {
failed_ss = ss;
goto out_cancel_attach;
@@ -2169,10 +2250,8 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
* being moved, this call will need to be reworked to communicate that.
*/
for_each_subsys(root, ss) {
- if (ss->attach) {
- tc = flex_array_get(group, 0);
- ss->attach(ss, cgrp, tc->cgrp, tc->task);
- }
+ if (ss->attach)
+ ss->attach(ss, cgrp, &tset);
}

/*
@@ -2194,11 +2273,11 @@ out_cancel_attach:
for_each_subsys(root, ss) {
if (ss == failed_ss) {
if (cancel_failed_ss && ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, leader);
+ ss->cancel_attach(ss, cgrp, &tset);
break;
}
if (ss->cancel_attach)
- ss->cancel_attach(ss, cgrp, leader);
+ ss->cancel_attach(ss, cgrp, &tset);
}
}
out_put_tasks:
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 4e82525..a2b0082 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -159,7 +159,7 @@ static void freezer_destroy(struct cgroup_subsys *ss,
*/
static int freezer_can_attach(struct cgroup_subsys *ss,
struct cgroup *new_cgroup,
- struct task_struct *task)
+ struct cgroup_taskset *tset)
{
struct freezer *freezer;

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 10131fd..2e5825b 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1368,10 +1368,10 @@ static int fmeter_getrate(struct fmeter *fmp)
}

/* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
-static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
- struct task_struct *tsk)
+static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+ struct cgroup_taskset *tset)
{
- struct cpuset *cs = cgroup_cs(cont);
+ struct cpuset *cs = cgroup_cs(cgrp);

if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
return -ENOSPC;
@@ -1384,7 +1384,7 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
* set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
* be changed.
*/
- if (tsk->flags & PF_THREAD_BOUND)
+ if (cgroup_taskset_first(tset)->flags & PF_THREAD_BOUND)
return -EINVAL;

return 0;
@@ -1434,12 +1434,14 @@ static void cpuset_attach_task(struct cgroup *cont, struct task_struct *tsk)
cpuset_update_task_spread_flag(cs, tsk);
}

-static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
- struct cgroup *oldcont, struct task_struct *tsk)
+static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
+ struct cgroup_taskset *tset)
{
struct mm_struct *mm;
- struct cpuset *cs = cgroup_cs(cont);
- struct cpuset *oldcs = cgroup_cs(oldcont);
+ struct task_struct *tsk = cgroup_taskset_first(tset);
+ struct cgroup *oldcgrp = cgroup_taskset_cur_cgroup(tset);
+ struct cpuset *cs = cgroup_cs(cgrp);
+ struct cpuset *oldcs = cgroup_cs(oldcgrp);

/*
* Change mm, possibly for multiple threads in a threadgroup. This is
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 930de94..b2802cc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5460,8 +5460,9 @@ static void mem_cgroup_clear_mc(void)

static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
struct cgroup *cgroup,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
+ struct task_struct *p = cgroup_taskset_first(tset);
int ret = 0;
struct mem_cgroup *mem = mem_cgroup_from_cont(cgroup);

@@ -5499,7 +5500,7 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,

static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
struct cgroup *cgroup,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
mem_cgroup_clear_mc();
}
@@ -5616,9 +5617,9 @@ retry:

static void mem_cgroup_move_task(struct cgroup_subsys *ss,
struct cgroup *cont,
- struct cgroup *old_cont,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
+ struct task_struct *p = cgroup_taskset_first(tset);
struct mm_struct *mm = get_task_mm(p);

if (mm) {
@@ -5633,19 +5634,18 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
#else /* !CONFIG_MMU */
static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
struct cgroup *cgroup,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
return 0;
}
static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
struct cgroup *cgroup,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
}
static void mem_cgroup_move_task(struct cgroup_subsys *ss,
struct cgroup *cont,
- struct cgroup *old_cont,
- struct task_struct *p)
+ struct cgroup_taskset *tset)
{
}
#endif
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 4450fbe..8b5b5d8 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -62,11 +62,12 @@ static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
struct cgroup_subsys devices_subsys;

static int devcgroup_can_attach(struct cgroup_subsys *ss,
- struct cgroup *new_cgroup, struct task_struct *task)
+ struct cgroup *new_cgrp, struct cgroup_taskset *set)
{
- if (current != task && !capable(CAP_SYS_ADMIN))
- return -EPERM;
+ struct task_struct *task = cgroup_taskset_first(set);

+ if (current != task && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
return 0;
}

--
1.7.6

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