Messages in this thread | | | From | Paul Menage <> | Date | Tue, 29 Mar 2011 16:27:19 -0700 | Subject | Re: [PATCH v8.5 3/3] cgroups: make procs file writable |
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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/
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