[PATCH v5 3/3] cgroups: make procs file writable
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From: Ben Blum on 11 Aug 2010 01:50 Makes procs file writable to move all threads by tgid at once From: Ben Blum <bblum(a)andrew.cmu.edu> 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 <bblum(a)andrew.cmu.edu> --- Documentation/cgroups/cgroups.txt | 13 + kernel/cgroup.c | 424 +++++++++++++++++++++++++++++++++---- 2 files changed, 387 insertions(+), 50 deletions(-) diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt index b34823f..5f3c707 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 e8b8f71..586dbb7 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1723,6 +1723,76 @@ int cgroup_can_attach_per_thread(struct cgroup *cgrp, struct task_struct *task, } EXPORT_SYMBOL_GPL(cgroup_can_attach_per_thread); +/* + * 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 @@ -1733,11 +1803,9 @@ EXPORT_SYMBOL_GPL(cgroup_can_attach_per_thread); */ 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 */ @@ -1761,46 +1829,16 @@ 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 @@ -1826,49 +1864,339 @@ 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 take the threadgroup_fork_lock + * of leader since attach_task_by_pid took a reference. + * threadgroup_fork_lock must be taken outside of tasklist_lock to match + * the order in the fork path. + */ + threadgroup_fork_write_lock(leader); + 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); + threadgroup_fork_write_unlock(leader); + 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) { + /* 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); + threadgroup_fork_write_unlock(leader); + + /* + * 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; } @@ -3203,9 +3531,9 @@ 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", -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |