This patch series is a revision of http://lkml.org/lkml/2010/5/29/126 .
These patches use an rwlock in signal_struct which access is dependent
on Oleg's recent changes to signal_struct's lifetime rules.
It is okay to write the tid of any task in the threadgroup. This is
implemented by taking task->group_leader right after find_task_by_vpid
while still rcu_read-side. This makes it necessary to check if
thread_group_leader(leader) every time we want to iterate over
->thread_group; each of these checks can fail with -EAGAIN.
Unfortunately this also means I needed to put these checks in can_attach
for each subsystem that needs to check each thread in the group.
I handle EAGAIN in the file's write handler, since hey, it's a super
expensive operation, might as well make it unbounded-time to boot - this
is optional and would work just as well with -EAGAIN sent to userspace.
-- bblum
---
Documentation/cgroups/cgroups.txt | 13 -
include/linux/cgroup.h | 15 -
include/linux/init_task.h | 9
include/linux/sched.h | 10
kernel/cgroup.c | 449 +++++++++++++++++++++++++++++++++-----
kernel/cgroup_freezer.c | 4
kernel/cpuset.c | 4
kernel/fork.c | 10
kernel/ns_cgroup.c | 4
kernel/sched.c | 4
10 files changed, 462 insertions(+), 60 deletions(-)
Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
From: Ben Blum <[email protected]>
This patch adds an rwsem that lives in a threadgroup's signal_struct that's
taken for reading in the fork path, under CONFIG_CGROUPS. If another part of
the kernel later wants to use such a locking mechanism, the CONFIG_CGROUPS
ifdefs should be changed to a higher-up flag that CGROUPS and the other system
would both depend on.
This is a pre-patch for cgroups-procs-write.patch.
Signed-off-by: Ben Blum <[email protected]>
---
include/linux/cgroup.h | 15 ++++++++++-----
include/linux/init_task.h | 9 +++++++++
include/linux/sched.h | 10 ++++++++++
kernel/cgroup.c | 23 +++++++++++++++++++++--
kernel/fork.c | 10 +++++++---
5 files changed, 57 insertions(+), 10 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 8f78073..196a703 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -31,10 +31,12 @@ extern void cgroup_lock(void);
extern int cgroup_lock_is_held(void);
extern bool cgroup_lock_live_group(struct cgroup *cgrp);
extern void cgroup_unlock(void);
-extern void cgroup_fork(struct task_struct *p);
+extern void cgroup_fork(struct task_struct *p, unsigned long clone_flags);
extern void cgroup_fork_callbacks(struct task_struct *p);
-extern void cgroup_post_fork(struct task_struct *p);
+extern void cgroup_post_fork(struct task_struct *p, unsigned long clone_flags);
extern void cgroup_exit(struct task_struct *p, int run_callbacks);
+extern void cgroup_fork_failed(struct task_struct *p, int run_callbacks,
+ unsigned long clone_flags);
extern int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry);
extern int cgroup_load_subsys(struct cgroup_subsys *ss);
@@ -613,11 +615,14 @@ unsigned short css_depth(struct cgroup_subsys_state *css);
static inline int cgroup_init_early(void) { return 0; }
static inline int cgroup_init(void) { return 0; }
-static inline void cgroup_fork(struct task_struct *p) {}
+static inline void cgroup_fork(struct task_struct *p,
+ unsigned long clone_flags) {}
static inline void cgroup_fork_callbacks(struct task_struct *p) {}
-static inline void cgroup_post_fork(struct task_struct *p) {}
+static inline void cgroup_post_fork(struct task_struct *p,
+ unsigned long clone_flags) {}
static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
-
+static inline void cgroup_fork_failed(struct task_struct *p, int callbacks,
+ unsigned long clone_flags) {}
static inline void cgroup_lock(void) {}
static inline void cgroup_unlock(void) {}
static inline int cgroupstats_build(struct cgroupstats *stats,
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index b1ed1cd..cfb2bc8 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -15,6 +15,14 @@
extern struct files_struct init_files;
extern struct fs_struct init_fs;
+#ifdef CONFIG_CGROUPS
+#define INIT_THREADGROUP_FORK_LOCK(sig) \
+ .threadgroup_fork_lock = \
+ __RWSEM_INITIALIZER(sig.threadgroup_fork_lock),
+#else
+#define INIT_THREADGROUP_FORK_LOCK(sig)
+#endif
+
#define INIT_SIGNALS(sig) { \
.count = ATOMIC_INIT(1), \
.wait_chldexit = __WAIT_QUEUE_HEAD_INITIALIZER(sig.wait_chldexit),\
@@ -29,6 +37,7 @@ extern struct fs_struct init_fs;
.running = 0, \
.lock = __SPIN_LOCK_UNLOCKED(sig.cputimer.lock), \
}, \
+ INIT_THREADGROUP_FORK_LOCK(sig) \
}
extern struct nsproxy init_nsproxy;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2b7b81d..2bbcbd2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -627,6 +627,16 @@ struct signal_struct {
unsigned audit_tty;
struct tty_audit_buf *tty_audit_buf;
#endif
+#ifdef CONFIG_CGROUPS
+ /*
+ * The threadgroup_fork_lock prevents threads from forking with
+ * CLONE_THREAD while held for writing. Use this for fork-sensitive
+ * threadgroup-wide operations.
+ * Currently only needed by cgroups, and the fork-side readlock happens
+ * in cgroup_{fork,post_fork,fork_failed}.
+ */
+ struct rw_semaphore threadgroup_fork_lock;
+#endif
int oom_adj; /* OOM kill score adjustment (bit shift) */
};
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 6d870f2..6c8e46f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4015,8 +4015,10 @@ static const struct file_operations proc_cgroupstats_operations = {
* At the point that cgroup_fork() is called, 'current' is the parent
* task, and the passed argument 'child' points to the child task.
*/
-void cgroup_fork(struct task_struct *child)
+void cgroup_fork(struct task_struct *child, unsigned long clone_flags)
{
+ if (clone_flags & CLONE_THREAD)
+ down_read(¤t->signal->threadgroup_fork_lock);
task_lock(current);
child->cgroups = current->cgroups;
get_css_set(child->cgroups);
@@ -4058,7 +4060,7 @@ void cgroup_fork_callbacks(struct task_struct *child)
* with the first call to cgroup_iter_start() - to guarantee that the
* new task ends up on its list.
*/
-void cgroup_post_fork(struct task_struct *child)
+void cgroup_post_fork(struct task_struct *child, unsigned long clone_flags)
{
if (use_task_css_set_links) {
write_lock(&css_set_lock);
@@ -4068,6 +4070,8 @@ void cgroup_post_fork(struct task_struct *child)
task_unlock(child);
write_unlock(&css_set_lock);
}
+ if (clone_flags & CLONE_THREAD)
+ up_read(¤t->signal->threadgroup_fork_lock);
}
/**
* cgroup_exit - detach cgroup from exiting task
@@ -4143,6 +4147,21 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
}
/**
+ * cgroup_fork_failed - undo operations for fork failure
+ * @tsk: pointer to task_struct of exiting process
+ * @run_callback: run exit callbacks?
+ *
+ * Wrapper for cgroup_exit that also drops the fork lock.
+ */
+void cgroup_fork_failed(struct task_struct *tsk, int run_callbacks,
+ unsigned long clone_flags)
+{
+ if (clone_flags & CLONE_THREAD)
+ up_read(¤t->signal->threadgroup_fork_lock);
+ cgroup_exit(tsk, run_callbacks);
+}
+
+/**
* cgroup_clone - clone the cgroup the given subsystem is attached to
* @tsk: the task to be moved
* @subsys: the given subsystem
diff --git a/kernel/fork.c b/kernel/fork.c
index 4c14942..e2b04ac 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -884,6 +884,10 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
tty_audit_fork(sig);
+#ifdef CONFIG_CGROUPS
+ init_rwsem(&sig->threadgroup_fork_lock);
+#endif
+
sig->oom_adj = current->signal->oom_adj;
return 0;
@@ -1069,7 +1073,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
monotonic_to_bootbased(&p->real_start_time);
p->io_context = NULL;
p->audit_context = NULL;
- cgroup_fork(p);
+ cgroup_fork(p, clone_flags);
#ifdef CONFIG_NUMA
p->mempolicy = mpol_dup(p->mempolicy);
if (IS_ERR(p->mempolicy)) {
@@ -1277,7 +1281,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
spin_unlock(¤t->sighand->siglock);
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
- cgroup_post_fork(p);
+ cgroup_post_fork(p, clone_flags);
perf_event_fork(p);
return p;
@@ -1311,7 +1315,7 @@ bad_fork_cleanup_policy:
mpol_put(p->mempolicy);
bad_fork_cleanup_cgroup:
#endif
- cgroup_exit(p, cgroup_callbacks_done);
+ cgroup_fork_failed(p, cgroup_callbacks_done, clone_flags);
delayacct_tsk_free(p);
module_put(task_thread_info(p)->exec_domain->module);
bad_fork_cleanup_count:
Makes procs file writable to move all threads by tgid at once
From: Ben Blum <[email protected]>
This patch adds functionality that enables users to move all threads in a
threadgroup at once to a cgroup by writing the tgid to the 'cgroup.procs'
file. This current implementation makes use of a per-threadgroup rwsem that's
taken for reading in the fork() path to prevent newly forking threads within
the threadgroup from "escaping" while the move is in progress.
Signed-off-by: Ben Blum <[email protected]>
---
Documentation/cgroups/cgroups.txt | 13 +
kernel/cgroup.c | 426 +++++++++++++++++++++++++++++++++----
kernel/cgroup_freezer.c | 4
kernel/cpuset.c | 4
kernel/ns_cgroup.c | 4
kernel/sched.c | 4
6 files changed, 405 insertions(+), 50 deletions(-)
diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index a1ca592..1d9c81e 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -235,7 +235,8 @@ containing the following files describing that cgroup:
- cgroup.procs: list of tgids in the cgroup. This list is not
guaranteed to be sorted or free of duplicate tgids, and userspace
should sort/uniquify the list if this property is required.
- This is a read-only file, for now.
+ Writing a thread group id into this file moves all threads in that
+ group into this cgroup.
- notify_on_release flag: run the release agent on exit?
- release_agent: the path to use for release notifications (this file
exists in the top cgroup only)
@@ -416,6 +417,12 @@ You can attach the current shell task by echoing 0:
# echo 0 > tasks
+You can use the cgroup.procs file instead of the tasks file to move all
+threads in a threadgroup at once. Echoing the pid of any task in a
+threadgroup to cgroup.procs causes all tasks in that threadgroup to be
+be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks
+in the writing task's threadgroup.
+
2.3 Mounting hierarchies by name
--------------------------------
@@ -564,7 +571,9 @@ 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. If threadgroup is
true, then a successful result indicates that all threads in the given
-thread's threadgroup can be moved together.
+thread's threadgroup can be moved together. If the subsystem wants to
+iterate over task->thread_group, it must take rcu_read_lock then check
+if thread_group_leader(task), returning -EAGAIN if that fails.
void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct task_struct *task, bool threadgroup)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 6c8e46f..526f44b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1686,6 +1686,76 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
}
EXPORT_SYMBOL_GPL(cgroup_path);
+/*
+ * cgroup_task_migrate - move a task from one cgroup to another.
+ *
+ * 'guarantee' is set if the caller promises that a new css_set for the task
+ * will already exit. If not set, this function might sleep, and can fail with
+ * -ENOMEM. Otherwise, it can only fail with -ESRCH.
+ */
+static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
+ struct task_struct *tsk, bool guarantee)
+{
+ struct css_set *oldcg;
+ struct css_set *newcg;
+
+ /*
+ * get old css_set. we need to take task_lock and refcount it, because
+ * an exiting task can change its css_set to init_css_set and drop its
+ * old one without taking cgroup_mutex.
+ */
+ task_lock(tsk);
+ oldcg = tsk->cgroups;
+ get_css_set(oldcg);
+ task_unlock(tsk);
+
+ /* locate or allocate a new css_set for this task. */
+ if (guarantee) {
+ /* we know the css_set we want already exists. */
+ struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+ read_lock(&css_set_lock);
+ newcg = find_existing_css_set(oldcg, cgrp, template);
+ BUG_ON(!newcg);
+ get_css_set(newcg);
+ read_unlock(&css_set_lock);
+ } else {
+ might_sleep();
+ /* find_css_set will give us newcg already referenced. */
+ newcg = find_css_set(oldcg, cgrp);
+ if (!newcg) {
+ put_css_set(oldcg);
+ return -ENOMEM;
+ }
+ }
+ put_css_set(oldcg);
+
+ /* if PF_EXITING is set, the tsk->cgroups pointer is no longer safe. */
+ task_lock(tsk);
+ if (tsk->flags & PF_EXITING) {
+ task_unlock(tsk);
+ put_css_set(newcg);
+ return -ESRCH;
+ }
+ rcu_assign_pointer(tsk->cgroups, newcg);
+ task_unlock(tsk);
+
+ /* Update the css_set linked lists if we're using them */
+ write_lock(&css_set_lock);
+ if (!list_empty(&tsk->cg_list))
+ list_move(&tsk->cg_list, &newcg->tasks);
+ write_unlock(&css_set_lock);
+
+ /*
+ * We just gained a reference on oldcg by taking it from the task. As
+ * trading it for newcg is protected by cgroup_mutex, we're safe to drop
+ * it here; it will be freed under RCU.
+ */
+ put_css_set(oldcg);
+
+ set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+ return 0;
+}
+
/**
* cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
* @cgrp: the cgroup the task is attaching to
@@ -1696,11 +1766,9 @@ EXPORT_SYMBOL_GPL(cgroup_path);
*/
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
- int retval = 0;
+ int retval;
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
- struct css_set *cg;
- struct css_set *newcg;
struct cgroupfs_root *root = cgrp->root;
/* Nothing to do if the task is already in that cgroup */
@@ -1724,46 +1792,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
}
}
- task_lock(tsk);
- cg = tsk->cgroups;
- get_css_set(cg);
- task_unlock(tsk);
- /*
- * Locate or allocate a new css_set for this task,
- * based on its final set of cgroups
- */
- newcg = find_css_set(cg, cgrp);
- put_css_set(cg);
- if (!newcg) {
- retval = -ENOMEM;
- goto out;
- }
-
- task_lock(tsk);
- if (tsk->flags & PF_EXITING) {
- task_unlock(tsk);
- put_css_set(newcg);
- retval = -ESRCH;
+ retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
+ if (retval)
goto out;
- }
- rcu_assign_pointer(tsk->cgroups, newcg);
- task_unlock(tsk);
-
- /* Update the css_set linked lists if we're using them */
- write_lock(&css_set_lock);
- if (!list_empty(&tsk->cg_list)) {
- list_del(&tsk->cg_list);
- list_add(&tsk->cg_list, &newcg->tasks);
- }
- write_unlock(&css_set_lock);
for_each_subsys(root, ss) {
if (ss->attach)
ss->attach(ss, cgrp, oldcgrp, tsk, false);
}
- set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+
synchronize_rcu();
- put_css_set(cg);
/*
* wake up rmdir() waiter. the rmdir should fail since the cgroup
@@ -1789,49 +1827,341 @@ out:
}
/*
- * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
- * held. May take task_lock of task
+ * cgroup_attach_proc works in two stages, the first of which prefetches all
+ * new css_sets needed (to make sure we have enough memory before committing
+ * to the move) and stores them in a list of entries of the following type.
+ * TODO: possible optimization: use css_set->rcu_head for chaining instead
+ */
+struct cg_list_entry {
+ struct css_set *cg;
+ struct list_head links;
+};
+
+static bool css_set_check_fetched(struct cgroup *cgrp,
+ struct task_struct *tsk, struct css_set *cg,
+ struct list_head *newcg_list)
+{
+ struct css_set *newcg;
+ struct cg_list_entry *cg_entry;
+ struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+
+ read_lock(&css_set_lock);
+ newcg = find_existing_css_set(cg, cgrp, template);
+ if (newcg)
+ get_css_set(newcg);
+ read_unlock(&css_set_lock);
+
+ /* doesn't exist at all? */
+ if (!newcg)
+ return false;
+ /* see if it's already in the list */
+ list_for_each_entry(cg_entry, newcg_list, links) {
+ if (cg_entry->cg == newcg) {
+ put_css_set(newcg);
+ return true;
+ }
+ }
+
+ /* not found */
+ put_css_set(newcg);
+ return false;
+}
+
+/*
+ * Find the new css_set and store it in the list in preparation for moving the
+ * given task to the given cgroup. Returns 0 or -ENOMEM.
*/
-static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
+static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
+ struct list_head *newcg_list)
+{
+ struct css_set *newcg;
+ struct cg_list_entry *cg_entry;
+
+ /* ensure a new css_set will exist for this thread */
+ newcg = find_css_set(cg, cgrp);
+ if (!newcg)
+ return -ENOMEM;
+ /* add it to the list */
+ cg_entry = kmalloc(sizeof(struct cg_list_entry), GFP_KERNEL);
+ if (!cg_entry) {
+ put_css_set(newcg);
+ return -ENOMEM;
+ }
+ cg_entry->cg = newcg;
+ list_add(&cg_entry->links, newcg_list);
+ return 0;
+}
+
+/**
+ * cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
+ * @cgrp: the cgroup to attach to
+ * @leader: the threadgroup leader task_struct of the group to be attached
+ *
+ * Call holding cgroup_mutex. Will take task_lock of each thread in leader's
+ * threadgroup individually in turn.
+ */
+int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
+{
+ int retval;
+ struct cgroup_subsys *ss, *failed_ss = NULL;
+ struct cgroup *oldcgrp;
+ struct css_set *oldcg;
+ struct cgroupfs_root *root = cgrp->root;
+ /* threadgroup list cursor */
+ struct task_struct *tsk;
+ /*
+ * 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
+ * case we get an ENOMEM we can bail out before making any changes.
+ */
+ struct list_head newcg_list;
+ struct cg_list_entry *cg_entry, *temp_nobe;
+
+ /* check that we can legitimately attach to the cgroup. */
+ for_each_subsys(root, ss) {
+ if (ss->can_attach) {
+ retval = ss->can_attach(ss, cgrp, leader, true);
+ if (retval) {
+ failed_ss = ss;
+ goto out;
+ }
+ }
+ }
+
+ /*
+ * step 1: make sure css_sets exist for all threads to be migrated.
+ * we use find_css_set, which allocates a new one if necessary.
+ */
+ INIT_LIST_HEAD(&newcg_list);
+ oldcgrp = task_cgroup_from_root(leader, root);
+ if (cgrp != oldcgrp) {
+ /* get old css_set */
+ task_lock(leader);
+ if (leader->flags & PF_EXITING) {
+ task_unlock(leader);
+ goto prefetch_loop;
+ }
+ oldcg = leader->cgroups;
+ get_css_set(oldcg);
+ task_unlock(leader);
+ /* acquire new one */
+ retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
+ put_css_set(oldcg);
+ if (retval)
+ goto list_teardown;
+ }
+prefetch_loop:
+ rcu_read_lock();
+ /* sanity check - if we raced with de_thread, we must abort */
+ if (!thread_group_leader(leader)) {
+ retval = -EAGAIN;
+ goto list_teardown;
+ }
+ /*
+ * if we need to fetch a new css_set for this task, we must exit the
+ * rcu_read section because allocating it can sleep. afterwards, we'll
+ * need to restart iteration on the threadgroup list - the whole thing
+ * will be O(nm) in the number of threads and css_sets; as the typical
+ * case has only one css_set for all of them, usually O(n). which ones
+ * we need allocated won't change as long as we hold cgroup_mutex.
+ */
+ list_for_each_entry_rcu(tsk, &leader->thread_group, thread_group) {
+ /* nothing to do if this task is already in the cgroup */
+ oldcgrp = task_cgroup_from_root(tsk, root);
+ if (cgrp == oldcgrp)
+ continue;
+ /* get old css_set pointer */
+ task_lock(tsk);
+ if (tsk->flags & PF_EXITING) {
+ /* ignore this task if it's going away */
+ task_unlock(tsk);
+ continue;
+ }
+ oldcg = tsk->cgroups;
+ get_css_set(oldcg);
+ task_unlock(tsk);
+ /* see if the new one for us is already in the list? */
+ if (css_set_check_fetched(cgrp, tsk, oldcg, &newcg_list)) {
+ /* was already there, nothing to do. */
+ put_css_set(oldcg);
+ } else {
+ /* we don't already have it. get new one. */
+ rcu_read_unlock();
+ retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
+ put_css_set(oldcg);
+ if (retval)
+ goto list_teardown;
+ /* begin iteration again. */
+ goto prefetch_loop;
+ }
+ }
+ rcu_read_unlock();
+
+ /*
+ * step 2: now that we're guaranteed success wrt the css_sets, proceed
+ * to move all tasks to the new cgroup. we need to lock against possible
+ * races with fork(). note: we can safely access leader->signal because
+ * attach_task_by_pid takes a reference on leader, which guarantees that
+ * the signal_struct will stick around. threadgroup_fork_lock must be
+ * taken outside of tasklist_lock to match the order in the fork path.
+ */
+ BUG_ON(!leader->signal);
+ down_write(&leader->signal->threadgroup_fork_lock);
+ read_lock(&tasklist_lock);
+ /* sanity check - if we raced with de_thread, we must abort */
+ if (!thread_group_leader(leader)) {
+ retval = -EAGAIN;
+ read_unlock(&tasklist_lock);
+ up_write(&leader->signal->threadgroup_fork_lock);
+ goto list_teardown;
+ }
+ /*
+ * No failure cases left, so this is the commit point.
+ *
+ * If the leader is already there, skip moving him. Note: even if the
+ * leader is PF_EXITING, we still move all other threads; if everybody
+ * is PF_EXITING, we end up doing nothing, which is ok.
+ */
+ oldcgrp = task_cgroup_from_root(leader, root);
+ if (cgrp != oldcgrp) {
+ retval = cgroup_task_migrate(cgrp, oldcgrp, leader, true);
+ BUG_ON(retval != 0 && retval != -ESRCH);
+ }
+ /* Now iterate over each thread in the group. */
+ list_for_each_entry_rcu(tsk, &leader->thread_group, thread_group) {
+ BUG_ON(tsk->signal != leader->signal);
+ /* leave current thread as it is if it's already there */
+ oldcgrp = task_cgroup_from_root(tsk, root);
+ if (cgrp == oldcgrp)
+ continue;
+ /* we don't care whether these threads are exiting */
+ retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
+ BUG_ON(retval != 0 && retval != -ESRCH);
+ }
+
+ /*
+ * step 3: attach whole threadgroup to each subsystem
+ * TODO: if ever a subsystem needs to know the oldcgrp for each task
+ * being moved, this call will need to be reworked to communicate that.
+ */
+ for_each_subsys(root, ss) {
+ if (ss->attach)
+ ss->attach(ss, cgrp, oldcgrp, leader, true);
+ }
+ /* holding these until here keeps us safe from exec() and fork(). */
+ read_unlock(&tasklist_lock);
+ up_write(&leader->signal->threadgroup_fork_lock);
+
+ /*
+ * step 4: success! and cleanup
+ */
+ synchronize_rcu();
+ cgroup_wakeup_rmdir_waiter(cgrp);
+ retval = 0;
+list_teardown:
+ /* clean up the list of prefetched css_sets. */
+ list_for_each_entry_safe(cg_entry, temp_nobe, &newcg_list, links) {
+ list_del(&cg_entry->links);
+ put_css_set(cg_entry->cg);
+ kfree(cg_entry);
+ }
+out:
+ if (retval) {
+ /* same deal as in cgroup_attach_task, with threadgroup=true */
+ for_each_subsys(root, ss) {
+ if (ss == failed_ss)
+ break;
+ if (ss->cancel_attach)
+ ss->cancel_attach(ss, cgrp, leader, true);
+ }
+ }
+ return retval;
+}
+
+/*
+ * Find the task_struct of the task to attach by vpid and pass it along to the
+ * function to attach either it or all tasks in its threadgroup. Will take
+ * cgroup_mutex; may take task_lock of task.
+ */
+static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
{
struct task_struct *tsk;
const struct cred *cred = current_cred(), *tcred;
int ret;
+ if (!cgroup_lock_live_group(cgrp))
+ return -ENODEV;
+
if (pid) {
rcu_read_lock();
tsk = find_task_by_vpid(pid);
- if (!tsk || tsk->flags & PF_EXITING) {
+ if (!tsk) {
+ rcu_read_unlock();
+ cgroup_unlock();
+ return -ESRCH;
+ }
+ if (threadgroup) {
+ /*
+ * it is safe to find group_leader because tsk was found
+ * in the tid map, meaning it can't have been unhashed
+ * by someone in de_thread changing the leadership.
+ */
+ tsk = tsk->group_leader;
+ BUG_ON(!thread_group_leader(tsk));
+ } else if (tsk->flags & PF_EXITING) {
+ /* optimization for the single-task-only case */
rcu_read_unlock();
+ cgroup_unlock();
return -ESRCH;
}
+ /*
+ * even if we're attaching all tasks in the thread group, we
+ * only need to check permissions on one of them.
+ */
tcred = __task_cred(tsk);
if (cred->euid &&
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
rcu_read_unlock();
+ cgroup_unlock();
return -EACCES;
}
get_task_struct(tsk);
rcu_read_unlock();
} else {
- tsk = current;
+ if (threadgroup)
+ tsk = current->group_leader;
+ else
+ tsk = current;
get_task_struct(tsk);
}
- ret = cgroup_attach_task(cgrp, tsk);
+ if (threadgroup)
+ ret = cgroup_attach_proc(cgrp, tsk);
+ else
+ ret = cgroup_attach_task(cgrp, tsk);
put_task_struct(tsk);
+ cgroup_unlock();
return ret;
}
static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
{
+ return attach_task_by_pid(cgrp, pid, false);
+}
+
+static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
+{
int ret;
- if (!cgroup_lock_live_group(cgrp))
- return -ENODEV;
- ret = attach_task_by_pid(cgrp, pid);
- cgroup_unlock();
+ do {
+ /*
+ * attach_proc fails with -EAGAIN if threadgroup leadership
+ * changes in the middle of the operation, in which case we need
+ * to find the task_struct for the new leader and start over.
+ */
+ ret = attach_task_by_pid(cgrp, tgid, true);
+ } while (ret == -EAGAIN);
return ret;
}
@@ -3167,9 +3497,9 @@ static struct cftype files[] = {
{
.name = CGROUP_FILE_GENERIC_PREFIX "procs",
.open = cgroup_procs_open,
- /* .write_u64 = cgroup_procs_write, TODO */
+ .write_u64 = cgroup_procs_write,
.release = cgroup_pidlist_release,
- .mode = S_IRUGO,
+ .mode = S_IRUGO | S_IWUSR,
},
{
.name = "notify_on_release",
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e5c0244..dfb9f24 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -185,6 +185,10 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
struct task_struct *c;
rcu_read_lock();
+ if (!thread_group_leader(task)) {
+ rcu_read_unlock();
+ return -EAGAIN;
+ }
list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
if (is_task_frozen_enough(c)) {
rcu_read_unlock();
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index d109467..edc7c01 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1360,6 +1360,10 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
struct task_struct *c;
rcu_read_lock();
+ if (!thread_group_leader(tsk)) {
+ rcu_read_unlock();
+ return -EAGAIN;
+ }
list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
ret = security_task_setscheduler(c, 0, NULL);
if (ret) {
diff --git a/kernel/ns_cgroup.c b/kernel/ns_cgroup.c
index 2a5dfec..ecd15d2 100644
--- a/kernel/ns_cgroup.c
+++ b/kernel/ns_cgroup.c
@@ -59,6 +59,10 @@ static int ns_can_attach(struct cgroup_subsys *ss, struct cgroup *new_cgroup,
if (threadgroup) {
struct task_struct *c;
rcu_read_lock();
+ if (!thread_group_leader(task)) {
+ rcu_read_unlock();
+ return -EAGAIN;
+ }
list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
if (!cgroup_is_descendant(new_cgroup, c)) {
rcu_read_unlock();
diff --git a/kernel/sched.c b/kernel/sched.c
index 3c2a54f..1b36bf0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8712,6 +8712,10 @@ cpu_cgroup_can_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
if (threadgroup) {
struct task_struct *c;
rcu_read_lock();
+ if (!thread_group_leader(tsk)) {
+ rcu_read_unlock();
+ return -EAGAIN;
+ }
list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
retval = cpu_cgroup_can_attach_task(cgrp, c);
if (retval) {
On Fri, 25 Jun 2010 01:46:54 -0400
Ben Blum <[email protected]> wrote:
> Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
>
> From: Ben Blum <[email protected]>
>
> This patch adds an rwsem that lives in a threadgroup's signal_struct that's
> taken for reading in the fork path, under CONFIG_CGROUPS. If another part of
> the kernel later wants to use such a locking mechanism, the CONFIG_CGROUPS
> ifdefs should be changed to a higher-up flag that CGROUPS and the other system
> would both depend on.
>
> This is a pre-patch for cgroups-procs-write.patch.
>
Hmm, at adding a new lock, please describe its semantics.
Following is my understanding, right ?
Lock range:
This rwsem is read-locked from cgroup_fork() to cgroup_post_fork().
Most of works for fork() are between cgroup_fork() and cgroup_post_for().
This means if sig->threadgroup_fork_lock is held, no new do_work() can
make progress in this process groups. This rwsem is held only when
CLONE_THREAD is in clone_flags. IOW, this rwsem is taken only at creating
new thread.
What we can do with this:
By locking sig->threadgroup_fork_lock, a code can visit _all_ threads
in a process group witout any races. So, if you want to implement an
atomic operation against a process, taking this lock is an idea.
For what:
To implement an atomic process move in cgroup, we need this lock.
Why this implemantation:
Considering cgroup, threads in a cgroup can be under several different
cgroup. So, we can't implement lock in cgroup-internal, we use signal
struct.
By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
seem good idea. How about a code like this ?
read_lock_thread_clone(current);
cgroup_fork();
.....
cgroup_post_fork();
read_unlock_thrad_clone(current);
We may have chances to move these lock to better position if cgroup is
an only user.
Thanks,
-Kame
On Mon, Jun 28, 2010 at 04:10:31PM +0900, KAMEZAWA Hiroyuki wrote:
> On Fri, 25 Jun 2010 01:46:54 -0400
> Ben Blum <[email protected]> wrote:
>
> > Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
> >
> > From: Ben Blum <[email protected]>
> >
> > This patch adds an rwsem that lives in a threadgroup's signal_struct that's
> > taken for reading in the fork path, under CONFIG_CGROUPS. If another part of
> > the kernel later wants to use such a locking mechanism, the CONFIG_CGROUPS
> > ifdefs should be changed to a higher-up flag that CGROUPS and the other system
> > would both depend on.
> >
> > This is a pre-patch for cgroups-procs-write.patch.
> >
>
> Hmm, at adding a new lock, please describe its semantics.
> Following is my understanding, right ?
>
> Lock range:
> This rwsem is read-locked from cgroup_fork() to cgroup_post_fork().
> Most of works for fork() are between cgroup_fork() and cgroup_post_for().
> This means if sig->threadgroup_fork_lock is held, no new do_work() can
> make progress in this process groups. This rwsem is held only when
> CLONE_THREAD is in clone_flags. IOW, this rwsem is taken only at creating
> new thread.
>
> What we can do with this:
> By locking sig->threadgroup_fork_lock, a code can visit _all_ threads
> in a process group witout any races. So, if you want to implement an
> atomic operation against a process, taking this lock is an idea.
>
> For what:
> To implement an atomic process move in cgroup, we need this lock.
All good. Should a description like this go in Documentation/ somewhere,
or above the declaration of the lock?
> Why this implemantation:
> Considering cgroup, threads in a cgroup can be under several different
> cgroup. So, we can't implement lock in cgroup-internal, we use signal
> struct.
Not entirely, though that's an additional restriction... The reason it's
in signal_struct: signal_struct is per-threadgroup and has exactly the
lifetime rules we want. Putting the lock in task_struct and taking
current->group_leader->signal... seems like it would also work, but
introduces cacheline conflicts that weren't there before, since fork
doesn't look at group_leader (but it does bump signal's count).
> By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
> seem good idea. How about a code like this ?
>
> read_lock_thread_clone(current);
> cgroup_fork();
> .....
> cgroup_post_fork();
> read_unlock_thrad_clone(current);
>
> We may have chances to move these lock to better position if cgroup is
> an only user.
I didn't do that out of a desire to change fork.c as little as possible,
but that does look better than what I've got. Those two functions should
be in fork.c under #ifdef CONFIG_CGROUPS.
>
> Thanks,
> -Kame
Thanks,
-- Ben
On Mon, Jun 28, 2010 at 11:43:59AM -0400, Ben Blum wrote:
> On Mon, Jun 28, 2010 at 04:10:31PM +0900, KAMEZAWA Hiroyuki wrote:
> > By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
> > seem good idea. How about a code like this ?
> >
> > read_lock_thread_clone(current);
> > cgroup_fork();
> > .....
> > cgroup_post_fork();
> > read_unlock_thrad_clone(current);
> >
> > We may have chances to move these lock to better position if cgroup is
> > an only user.
>
> I didn't do that out of a desire to change fork.c as little as possible,
> but that does look better than what I've got. Those two functions should
> be in fork.c under #ifdef CONFIG_CGROUPS.
I'm looking at this now and am not sure where the best place to put
these is:
1) Don't make new functions, just put:
#ifdef CONFIG_CGROUPS
if (clone_flags & CLONE_THREAD)
down/up_read(...);
#endif
directly in copy_process() in fork.c. Simplest, but uglifies the code.
2) Make static helper functions in fork.c. Good, but not consistent with
directly using the lock in write-side (attach_proc).
3) Define inline functions under #ifdef CONFIG_CGROUPS in sched.h, just
under the declaration of the lock. Most robust, but I'm hesitant to add
unneeded stuff to such a popular header file.
Any opinions?
-- Ben
>
> >
> > Thanks,
> > -Kame
>
> Thanks,
> -- Ben
>
On Wed, 28 Jul 2010 04:29:53 -0400
Ben Blum <[email protected]> wrote:
> On Mon, Jun 28, 2010 at 11:43:59AM -0400, Ben Blum wrote:
> > On Mon, Jun 28, 2010 at 04:10:31PM +0900, KAMEZAWA Hiroyuki wrote:
> > > By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
> > > seem good idea. How about a code like this ?
> > >
> > > read_lock_thread_clone(current);
> > > cgroup_fork();
> > > .....
> > > cgroup_post_fork();
> > > read_unlock_thrad_clone(current);
> > >
> > > We may have chances to move these lock to better position if cgroup is
> > > an only user.
> >
> > I didn't do that out of a desire to change fork.c as little as possible,
> > but that does look better than what I've got. Those two functions should
> > be in fork.c under #ifdef CONFIG_CGROUPS.
>
> I'm looking at this now and am not sure where the best place to put
> these is:
>
> 1) Don't make new functions, just put:
>
> #ifdef CONFIG_CGROUPS
> if (clone_flags & CLONE_THREAD)
> down/up_read(...);
> #endif
>
> directly in copy_process() in fork.c. Simplest, but uglifies the code.
>
> 2) Make static helper functions in fork.c. Good, but not consistent with
> directly using the lock in write-side (attach_proc).
>
> 3) Define inline functions under #ifdef CONFIG_CGROUPS in sched.h, just
> under the declaration of the lock. Most robust, but I'm hesitant to add
> unneeded stuff to such a popular header file.
>
> Any opinions?
>
My point was simple. Because copy_process() is very important path,
the new lock should be visible in copy_process() or kernek/fork.c.
"If the lock is visible in copy_process(), the reader can notice it".
Then, I offer you 2 options.
rename cgroup_fork() and cgroup_post_fork() as
cgroup_fork_lock() and cgroup_post_fork_unlock()
Now, the lock is visible and the change is minimum.
Or
add the definition of lock/unlock to cgroup.h and include it
from kernel/fork.c
Thanks,
-Kame
On Wed, Jul 28, 2010 at 06:28:13PM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 28 Jul 2010 04:29:53 -0400
> Ben Blum <[email protected]> wrote:
>
> > On Mon, Jun 28, 2010 at 11:43:59AM -0400, Ben Blum wrote:
> > > On Mon, Jun 28, 2010 at 04:10:31PM +0900, KAMEZAWA Hiroyuki wrote:
> > > > By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
> > > > seem good idea. How about a code like this ?
> > > >
> > > > read_lock_thread_clone(current);
> > > > cgroup_fork();
> > > > .....
> > > > cgroup_post_fork();
> > > > read_unlock_thrad_clone(current);
> > > >
> > > > We may have chances to move these lock to better position if cgroup is
> > > > an only user.
> > >
> > > I didn't do that out of a desire to change fork.c as little as possible,
> > > but that does look better than what I've got. Those two functions should
> > > be in fork.c under #ifdef CONFIG_CGROUPS.
> >
> > I'm looking at this now and am not sure where the best place to put
> > these is:
> >
> > 1) Don't make new functions, just put:
> >
> > #ifdef CONFIG_CGROUPS
> > if (clone_flags & CLONE_THREAD)
> > down/up_read(...);
> > #endif
> >
> > directly in copy_process() in fork.c. Simplest, but uglifies the code.
> >
> > 2) Make static helper functions in fork.c. Good, but not consistent with
> > directly using the lock in write-side (attach_proc).
> >
> > 3) Define inline functions under #ifdef CONFIG_CGROUPS in sched.h, just
> > under the declaration of the lock. Most robust, but I'm hesitant to add
> > unneeded stuff to such a popular header file.
> >
> > Any opinions?
> >
>
> My point was simple. Because copy_process() is very important path,
> the new lock should be visible in copy_process() or kernek/fork.c.
> "If the lock is visible in copy_process(), the reader can notice it".
>
> Then, I offer you 2 options.
>
> rename cgroup_fork() and cgroup_post_fork() as
> cgroup_fork_lock() and cgroup_post_fork_unlock()
>
> Now, the lock is visible and the change is minimum.
>
> Or
> add the definition of lock/unlock to cgroup.h and include it
> from kernel/fork.c
>
> Thanks,
> -Kame
I don't like either of these. Renaming to cgroup_fork_lock not only
conveys the sense that a cgroup-specific lock is taken, but also hides
the real purpose of these functions, which is to manipulate cgroup
pointers. And it's not a cgroup-specific lock - only write-side is
*currently* used by cgroups - so it shouldn't go in cgroup.h.
-- Ben