diff options
| -rw-r--r-- | include/linux/cgroup.h | 10 | ||||
| -rw-r--r-- | kernel/cgroup.c | 359 |
2 files changed, 368 insertions, 1 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 60735dcf427..e2dd44f68f9 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -144,6 +144,16 @@ int cgroup_is_removed(const struct cgroup *cont); int cgroup_path(const struct cgroup *cont, char *buf, int buflen); +int __cgroup_task_count(const struct cgroup *cont); +static inline int cgroup_task_count(const struct cgroup *cont) +{ + int task_count; + rcu_read_lock(); + task_count = __cgroup_task_count(cont); + rcu_read_unlock(); + return task_count; +} + /* Return true if the cgroup is a descendant of the current cgroup */ int cgroup_is_descendant(const struct cgroup *cont); diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6ba857bec71..356c40d5d20 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -40,7 +40,7 @@ #include <linux/magic.h> #include <linux/spinlock.h> #include <linux/string.h> - +#include <linux/sort.h> #include <asm/atomic.h> /* Generate an array of cgroup subsystem pointers */ @@ -700,6 +700,127 @@ int cgroup_path(const struct cgroup *cont, char *buf, int buflen) return 0; } +/* + * Return the first subsystem attached to a cgroup's hierarchy, and + * its subsystem id. + */ + +static void get_first_subsys(const struct cgroup *cont, + struct cgroup_subsys_state **css, int *subsys_id) +{ + const struct cgroupfs_root *root = cont->root; + const struct cgroup_subsys *test_ss; + BUG_ON(list_empty(&root->subsys_list)); + test_ss = list_entry(root->subsys_list.next, + struct cgroup_subsys, sibling); + if (css) { + *css = cont->subsys[test_ss->subsys_id]; + BUG_ON(!*css); + } + if (subsys_id) + *subsys_id = test_ss->subsys_id; +} + +/* + * Attach task 'tsk' to cgroup 'cont' + * + * Call holding cgroup_mutex. May take task_lock of + * the task 'pid' during call. + */ +static int attach_task(struct cgroup *cont, struct task_struct *tsk) +{ + int retval = 0; + struct cgroup_subsys *ss; + struct cgroup *oldcont; + struct css_set *cg = &tsk->cgroups; + struct cgroupfs_root *root = cont->root; + int i; + int subsys_id; + + get_first_subsys(cont, NULL, &subsys_id); + + /* Nothing to do if the task is already in that cgroup */ + oldcont = task_cgroup(tsk, subsys_id); + if (cont == oldcont) + return 0; + + for_each_subsys(root, ss) { + if (ss->can_attach) { + retval = ss->can_attach(ss, cont, tsk); + if (retval) { + return retval; + } + } + } + + task_lock(tsk); + if (tsk->flags & PF_EXITING) { + task_unlock(tsk); + return -ESRCH; + } + /* Update the css_set pointers for the subsystems in this + * hierarchy */ + for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) { + if (root->subsys_bits & (1ull << i)) { + /* Subsystem is in this hierarchy. So we want + * the subsystem state from the new + * cgroup. Transfer the refcount from the + * old to the new */ + atomic_inc(&cont->count); + atomic_dec(&cg->subsys[i]->cgroup->count); + rcu_assign_pointer(cg->subsys[i], cont->subsys[i]); + } + } + task_unlock(tsk); + + for_each_subsys(root, ss) { + if (ss->attach) { + ss->attach(ss, cont, oldcont, tsk); + } + } + + synchronize_rcu(); + return 0; +} + +/* + * Attach task with pid 'pid' to cgroup 'cont'. Call with + * cgroup_mutex, may take task_lock of task + */ +static int attach_task_by_pid(struct cgroup *cont, char *pidbuf) +{ + pid_t pid; + struct task_struct *tsk; + int ret; + + if (sscanf(pidbuf, "%d", &pid) != 1) + return -EIO; + + if (pid) { + rcu_read_lock(); + tsk = find_task_by_pid(pid); + if (!tsk || tsk->flags & PF_EXITING) { + rcu_read_unlock(); + return -ESRCH; + } + get_task_struct(tsk); + rcu_read_unlock(); + + if ((current->euid) && (current->euid != tsk->uid) + && (current->euid != tsk->suid)) { + put_task_struct(tsk); + return -EACCES; + } + } else { + tsk = current; + get_task_struct(tsk); + } + + ret = attach_task(cont, tsk); + put_task_struct(tsk); + return ret; +} + /* The various types of files and directories in a cgroup file system */ enum cgroup_filetype { @@ -708,6 +829,55 @@ enum cgroup_filetype { FILE_TASKLIST, }; +static ssize_t cgroup_common_file_write(struct cgroup *cont, + struct cftype *cft, + struct file *file, + const char __user *userbuf, + size_t nbytes, loff_t *unused_ppos) +{ + enum cgroup_filetype type = cft->private; + char *buffer; + int retval = 0; + + if (nbytes >= PATH_MAX) + return -E2BIG; + + /* +1 for nul-terminator */ + buffer = kmalloc(nbytes + 1, GFP_KERNEL); + if (buffer == NULL) + return -ENOMEM; + + if (copy_from_user(buffer, userbuf, nbytes)) { + retval = -EFAULT; + goto out1; + } + buffer[nbytes] = 0; /* nul-terminate */ + + mutex_lock(&cgroup_mutex); + + if (cgroup_is_removed(cont)) { + retval = -ENODEV; + goto out2; + } + + switch (type) { + case FILE_TASKLIST: + retval = attach_task_by_pid(cont, buffer); + break; + default: + retval = -EINVAL; + goto out2; + } + + if (retval == 0) + retval = nbytes; +out2: + mutex_unlock(&cgroup_mutex); +out1: + kfree(buffer); + return retval; +} + static ssize_t cgroup_file_write(struct file *file, const char __user *buf, size_t nbytes, loff_t *ppos) { @@ -914,6 +1084,189 @@ int cgroup_add_files(struct cgroup *cont, return 0; } +/* Count the number of tasks in a cgroup. Could be made more + * time-efficient but less space-efficient with more linked lists + * running through each cgroup and the css_set structures that + * referenced it. Must be called with tasklist_lock held for read or + * write or in an rcu critical section. + */ +int __cgroup_task_count(const struct cgroup *cont) +{ + int count = 0; + struct task_struct *g, *p; + struct cgroup_subsys_state *css; + int subsys_id; + + get_first_subsys(cont, &css, &subsys_id); + do_each_thread(g, p) { + if (task_subsys_state(p, subsys_id) == css) + count ++; + } while_each_thread(g, p); + return count; +} + +/* + * Stuff for reading the 'tasks' file. + * + * Reading this file can return large amounts of data if a cgroup has + * *lots* of attached tasks. So it may need several calls to read(), + * but we cannot guarantee that the information we produce is correct + * unless we produce it entirely atomically. + * + * Upon tasks file open(), a struct ctr_struct is allocated, that + * will have a pointer to an array (also allocated here). The struct + * ctr_struct * is stored in file->private_data. Its resources will + * be freed by release() when the file is closed. The array is used + * to sprintf the PIDs and then used by read(). + */ +struct ctr_struct { + char *buf; + int bufsz; +}; + +/* + * Load into 'pidarray' up to 'npids' of the tasks using cgroup + * 'cont'. Return actual number of pids loaded. No need to + * task_lock(p) when reading out p->cgroup, since we're in an RCU + * read section, so the css_set can't go away, and is + * immutable after creation. + */ +static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cont) +{ + int n = 0; + struct task_struct *g, *p; + struct cgroup_subsys_state *css; + int subsys_id; + + get_first_subsys(cont, &css, &subsys_id); + rcu_read_lock(); + do_each_thread(g, p) { + if (task_subsys_state(p, subsys_id) == css) { + pidarray[n++] = pid_nr(task_pid(p)); + if (unlikely(n == npids)) + goto array_full; + } + } while_each_thread(g, p); + +array_full: + rcu_read_unlock(); + return n; +} + +static int cmppid(const void *a, const void *b) +{ + return *(pid_t *)a - *(pid_t *)b; +} + +/* + * Convert array 'a' of 'npids' pid_t's to a string of newline separated + * decimal pids in 'buf'. Don't write more than 'sz' chars, but return + * count 'cnt' of how many chars would be written if buf were large enough. + */ +static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids) +{ + int cnt = 0; + int i; + + for (i = 0; i < npids; i++) + cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]); + return cnt; +} + +/* + * Handle an open on 'tasks' file. Prepare a buffer listing the + * process id's of tasks currently attached to the cgroup being opened. + * + * Does not require any specific cgroup mutexes, and does not take any. + */ +static int cgroup_tasks_open(struct inode *unused, struct file *file) +{ + struct cgroup *cont = __d_cont(file->f_dentry->d_parent); + struct ctr_struct *ctr; + pid_t *pidarray; + int npids; + char c; + + if (!(file->f_mode & FMODE_READ)) + return 0; + + ctr = kmalloc(sizeof(*ctr), GFP_KERNEL); + if (!ctr) + goto err0; + + /* + * If cgroup gets more users after we read count, we won't have + * enough space - tough. This race is indistinguishable to the + * caller from the case that the additional cgroup users didn't + * show up until sometime later on. + */ + npids = cgroup_task_count(cont); + if (npids) { + pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL); + if (!pidarray) + goto err1; + + npids = pid_array_load(pidarray, npids, cont); + sort(pidarray, npids, sizeof(pid_t), cmppid, NULL); + + /* Call pid_array_to_buf() twice, first just to get bufsz */ + ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1; + ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL); + if (!ctr->buf) + goto err2; + ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids); + + kfree(pidarray); + } else { + ctr->buf = 0; + ctr->bufsz = 0; + } + file->private_data = ctr; + return 0; + +err2: + kfree(pidarray); +err1: + kfree(ctr); +err0: + return -ENOMEM; +} + +static ssize_t cgroup_tasks_read(struct cgroup *cont, + struct cftype *cft, + struct file *file, char __user *buf, + size_t nbytes, loff_t *ppos) +{ + struct ctr_struct *ctr = file->private_data; + + return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz); +} + +static int cgroup_tasks_release(struct inode *unused_inode, + struct file *file) +{ + struct ctr_struct *ctr; + + if (file->f_mode & FMODE_READ) { + ctr = file->private_data; + kfree(ctr->buf); + kfree(ctr); + } + return 0; +} + +/* + * for the common functions, 'private' gives the type of file + */ +static struct cftype cft_tasks = { + .name = "tasks", + .open = cgroup_tasks_open, + .read = cgroup_tasks_read, + .write = cgroup_common_file_write, + .release = cgroup_tasks_release, + .private = FILE_TASKLIST, +}; + static int cgroup_populate_dir(struct cgroup *cont) { int err; @@ -922,6 +1275,10 @@ static int cgroup_populate_dir(struct cgroup *cont) /* First clear out any existing files */ cgroup_clear_directory(cont->dentry); + err = cgroup_add_file(cont, NULL, &cft_tasks); + if (err < 0) + return err; + for_each_subsys(cont->root, ss) { if (ss->populate && (err = ss->populate(ss, cont)) < 0) return err; |