lkml.org 
[lkml]   [2011]   [Mar]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v8.5 3/3] cgroups: make procs file writable
On Mon, Mar 21, 2011 at 10:18 PM, Ben Blum <bblum@andrew.cmu.edu> wrote:
> Makes procs file writable to move all threads by tgid at once
>
> From: Ben Blum <bblum@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@andrew.cmu.edu>

Reviewed-by: Paul Menage <menage@google.com>

OK, I guess this is ready to go in :-)

Paul

> ---
>  Documentation/cgroups/cgroups.txt |    9 +
>  kernel/cgroup.c                   |  441 +++++++++++++++++++++++++++++++++----
>  2 files changed, 401 insertions(+), 49 deletions(-)
>
> diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
> index d3c9a24..92d93d6 100644
> --- a/Documentation/cgroups/cgroups.txt
> +++ b/Documentation/cgroups/cgroups.txt
> @@ -236,7 +236,8 @@ 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)
> @@ -426,6 +427,12 @@ 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
>  --------------------------------
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 616f27a..273633c 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1726,6 +1726,76 @@ 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 exist. 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
> @@ -1736,11 +1806,9 @@ 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 */
> @@ -1771,38 +1839,9 @@ 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->pre_attach)
> @@ -1812,9 +1851,8 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
>                if (ss->attach)
>                        ss->attach(ss, cgrp, oldcgrp, tsk);
>        }
> -       set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
> +
>        synchronize_rcu();
> -       put_css_set(cg);
>
>        /*
>         * wake up rmdir() waiter. the rmdir should fail since the cgroup
> @@ -1864,49 +1902,356 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
>  EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
>
>  /*
> - * 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 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 and the threadgroup_fork_lock of the leader. 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, i, group_size;
> +       struct cgroup_subsys *ss, *failed_ss = NULL;
> +       bool cancel_failed_ss = false;
> +       /* guaranteed to be initialized later, but the compiler needs this */
> +       struct cgroup *oldcgrp = NULL;
> +       struct css_set *oldcg;
> +       struct cgroupfs_root *root = cgrp->root;
> +       /* threadgroup list cursor and array */
> +       struct task_struct *tsk;
> +       struct task_struct **group;
> +       /*
> +        * 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;
> +
> +       /*
> +        * step 0: in order to do expensive, possibly blocking operations for
> +        * every thread, we cannot iterate the thread group list, since it needs
> +        * rcu or tasklist locked. instead, build an array of all threads in the
> +        * group - threadgroup_fork_lock prevents new threads from appearing,
> +        * and if threads exit, this will just be an over-estimate.
> +        */
> +       group_size = get_nr_threads(leader);
> +       group = kmalloc(group_size * sizeof(*group), GFP_KERNEL);
> +       if (!group)
> +               return -ENOMEM;
> +
> +       /* prevent changes to the threadgroup list while we take a snapshot. */
> +       rcu_read_lock();
> +       if (!thread_group_leader(leader)) {
> +               /*
> +                * a race with de_thread from another thread's exec() may strip
> +                * us of our leadership, making while_each_thread unsafe to use
> +                * on this task. if this happens, there is no choice but to
> +                * throw this task away and try again (from cgroup_procs_write);
> +                * this is "double-double-toil-and-trouble-check locking".
> +                */
> +               rcu_read_unlock();
> +               retval = -EAGAIN;
> +               goto out_free_group_list;
> +       }
> +       /* take a reference on each task in the group to go in the array. */
> +       tsk = leader;
> +       i = 0;
> +       do {
> +               /* as per above, nr_threads may decrease, but not increase. */
> +               BUG_ON(i >= group_size);
> +               get_task_struct(tsk);
> +               group[i] = tsk;
> +               i++;
> +       } while_each_thread(leader, tsk);
> +       /* remember the number of threads in the array for later. */
> +       group_size = i;
> +       rcu_read_unlock();
> +
> +       /*
> +        * step 1: 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);
> +                       if (retval) {
> +                               failed_ss = ss;
> +                               goto out_cancel_attach;
> +                       }
> +               }
> +               /* a callback to be run on every thread in the threadgroup. */
> +               if (ss->can_attach_task) {
> +                       /* run on each task in the threadgroup. */
> +                       for (i = 0; i < group_size; i++) {
> +                               retval = ss->can_attach_task(cgrp, group[i]);
> +                               if (retval) {
> +                                       failed_ss = ss;
> +                                       cancel_failed_ss = true;
> +                                       goto out_cancel_attach;
> +                               }
> +                       }
> +               }
> +       }
> +
> +       /*
> +        * step 2: 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);
> +       for (i = 0; i < group_size; i++) {
> +               tsk = group[i];
> +               /* 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. */
> +                       retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
> +                       put_css_set(oldcg);
> +                       if (retval)
> +                               goto out_list_teardown;
> +               }
> +       }
> +
> +       /*
> +        * step 3: now that we're guaranteed success wrt the css_sets, proceed
> +        * to move all tasks to the new cgroup, calling ss->attach_task for each
> +        * one along the way. there are no failure cases after here, so this is
> +        * the commit point.
> +        */
> +       for_each_subsys(root, ss) {
> +               if (ss->pre_attach)
> +                       ss->pre_attach(cgrp);
> +       }
> +       for (i = 0; i < group_size; i++) {
> +               tsk = group[i];
> +               /* leave current thread as it is if it's already there */
> +               oldcgrp = task_cgroup_from_root(tsk, root);
> +               if (cgrp == oldcgrp)
> +                       continue;
> +               /* attach each task to each subsystem */
> +               for_each_subsys(root, ss) {
> +                       if (ss->attach_task)
> +                               ss->attach_task(cgrp, tsk);
> +               }
> +               /* if the thread is PF_EXITING, it can just get skipped. */
> +               retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
> +               BUG_ON(retval != 0 && retval != -ESRCH);
> +       }
> +       /* nothing is sensitive to fork() after this point. */
> +
> +       /*
> +        * step 4: do expensive, non-thread-specific subsystem callbacks.
> +        * 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);
> +       }
> +
> +       /*
> +        * step 5: success! and cleanup
> +        */
> +       synchronize_rcu();
> +       cgroup_wakeup_rmdir_waiter(cgrp);
> +       retval = 0;
> +out_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_cancel_attach:
> +       /* same deal as in cgroup_attach_task */
> +       if (retval) {
> +               for_each_subsys(root, ss) {
> +                       if (ss == failed_ss) {
> +                               if (cancel_failed_ss && ss->cancel_attach)
> +                                       ss->cancel_attach(ss, cgrp, leader);
> +                               break;
> +                       }
> +                       if (ss->cancel_attach)
> +                               ss->cancel_attach(ss, cgrp, leader);
> +               }
> +       }
> +       /* clean up the array of referenced threads in the group. */
> +       for (i = 0; i < group_size; i++)
> +               put_task_struct(group[i]);
> +out_free_group_list:
> +       kfree(group);
> +       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)
> +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) {
> +                       /*
> +                        * RCU protects this access, since tsk was found in the
> +                        * tid map. a race with de_thread may cause group_leader
> +                        * to stop being the leader, but cgroup_attach_proc will
> +                        * detect it later.
> +                        */
> +                       tsk = tsk->group_leader;
> +               } 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) {
> +               threadgroup_fork_write_lock(tsk);
> +               ret = cgroup_attach_proc(cgrp, tsk);
> +               threadgroup_fork_write_unlock(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;
>  }
>
> @@ -3260,9 +3605,9 @@ 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@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-03-30 01:31    [W:0.117 / U:71.296 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site