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cgroups: add a read-only "procs" file similar to "tasks" that shows only unique tgids

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struct cgroup used to have a bunch of fields for keeping track of the
pidlist for the tasks file.  Those are now separated into a new struct
cgroup_pidlist, of which two are had, one for procs and one for tasks.
The way the seq_file operations are set up is changed so that just the
pidlist struct gets passed around as the private data.

Interface example: Suppose a multithreaded process has pid 1000 and other
threads with ids 1001, 1002, 1003:
$ cat tasks
1000
1001
1002
1003
$ cat cgroup.procs
1000
$

Signed-off-by: Ben Blum <bblum@google.com>
Signed-off-by: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ben Blum 2009-09-23 15:56:26 -07:00 committed by Linus Torvalds
parent 8f3ff20862
commit 102a775e36
2 changed files with 186 additions and 114 deletions
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22
include/linux/cgroup.h
View file

@ -141,6 +141,17 @@ enum {
CGRP_WAIT_ON_RMDIR,
};
struct cgroup_pidlist {
/* protects the other fields */
struct rw_semaphore mutex;
/* array of xids */
pid_t *list;
/* how many elements the above list has */
int length;
/* how many files are using the current array */
int use_count;
};
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */
@ -179,14 +190,9 @@ struct cgroup {
*/
struct list_head release_list;
/* pids_mutex protects the fields below */
struct rw_semaphore pids_mutex;
/* Array of process ids in the cgroup */
pid_t *tasks_pids;
/* How many files are using the current tasks_pids array */
int pids_use_count;
/* Length of the current tasks_pids array */
int pids_length;
/* we will have two separate pidlists, one for pids (the tasks file)
* and one for tgids (the procs file). */
struct cgroup_pidlist tasks, procs;
/* For RCU-protected deletion */
struct rcu_head rcu_head;

278
kernel/cgroup.c
View file

@ -1121,7 +1121,8 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
INIT_LIST_HEAD(&cgrp->children);
INIT_LIST_HEAD(&cgrp->css_sets);
INIT_LIST_HEAD(&cgrp->release_list);
init_rwsem(&cgrp->pids_mutex);
init_rwsem(&(cgrp->tasks.mutex));
init_rwsem(&(cgrp->procs.mutex));
}
static void init_cgroup_root(struct cgroupfs_root *root)
@ -1637,15 +1638,6 @@ static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
return ret;
}
/* The various types of files and directories in a cgroup file system */
enum cgroup_filetype {
FILE_ROOT,
FILE_DIR,
FILE_TASKLIST,
FILE_NOTIFY_ON_RELEASE,
FILE_RELEASE_AGENT,
};
/**
* cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
* @cgrp: the cgroup to be checked for liveness
@ -2343,7 +2335,7 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
}
/*
* Stuff for reading the 'tasks' file.
* Stuff for reading the 'tasks'/'procs' files.
*
* 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(),
@ -2353,27 +2345,106 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
*/
/*
* Load into 'pidarray' up to 'npids' of the tasks using cgroup
* 'cgrp'. 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.
* pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
* If the new stripped list is sufficiently smaller and there's enough memory
* to allocate a new buffer, will let go of the unneeded memory. Returns the
* number of unique elements.
*/
static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp)
/* is the size difference enough that we should re-allocate the array? */
#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))
static int pidlist_uniq(pid_t **p, int length)
{
int n = 0, pid;
int src, dest = 1;
pid_t *list = *p;
pid_t *newlist;
/*
* we presume the 0th element is unique, so i starts at 1. trivial
* edge cases first; no work needs to be done for either
*/
if (length == 0 || length == 1)
return length;
/* src and dest walk down the list; dest counts unique elements */
for (src = 1; src < length; src++) {
/* find next unique element */
while (list[src] == list[src-1]) {
src++;
if (src == length)
goto after;
}
/* dest always points to where the next unique element goes */
list[dest] = list[src];
dest++;
}
after:
/*
* if the length difference is large enough, we want to allocate a
* smaller buffer to save memory. if this fails due to out of memory,
* we'll just stay with what we've got.
*/
if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
newlist = krealloc(list, dest * sizeof(pid_t), GFP_KERNEL);
if (newlist)
*p = newlist;
}
return dest;
}
static int cmppid(const void *a, const void *b)
{
return *(pid_t *)a - *(pid_t *)b;
}
/*
* Load a cgroup's pidarray with either procs' tgids or tasks' pids
*/
static int pidlist_array_load(struct cgroup *cgrp, bool procs)
{
pid_t *array;
int length;
int pid, n = 0; /* used for populating the array */
struct cgroup_iter it;
struct task_struct *tsk;
struct cgroup_pidlist *l;
/*
* 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.
*/
length = cgroup_task_count(cgrp);
array = kmalloc(length * sizeof(pid_t), GFP_KERNEL);
if (!array)
return -ENOMEM;
/* now, populate the array */
cgroup_iter_start(cgrp, &it);
while ((tsk = cgroup_iter_next(cgrp, &it))) {
if (unlikely(n == npids))
if (unlikely(n == length))
break;
pid = task_pid_vnr(tsk);
if (pid > 0)
pidarray[n++] = pid;
/* get tgid or pid for procs or tasks file respectively */
pid = (procs ? task_tgid_vnr(tsk) : task_pid_vnr(tsk));
if (pid > 0) /* make sure to only use valid results */
array[n++] = pid;
}
cgroup_iter_end(cgrp, &it);
return n;
length = n;
/* now sort & (if procs) strip out duplicates */
sort(array, length, sizeof(pid_t), cmppid, NULL);
if (procs) {
length = pidlist_uniq(&array, length);
l = &(cgrp->procs);
} else {
l = &(cgrp->tasks);
}
/* store array in cgroup, freeing old if necessary */
down_write(&l->mutex);
kfree(l->list);
l->list = array;
l->length = length;
l->use_count++;
up_write(&l->mutex);
return 0;
}
/**
@ -2430,19 +2501,14 @@ err:
return ret;
}
static int cmppid(const void *a, const void *b)
{
return *(pid_t *)a - *(pid_t *)b;
}
/*
* seq_file methods for the "tasks" file. The seq_file position is the
* seq_file methods for the tasks/procs files. The seq_file position is the
* next pid to display; the seq_file iterator is a pointer to the pid
* in the cgroup->tasks_pids array.
* in the cgroup->l->list array.
*/
static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos)
{
/*
* Initially we receive a position value that corresponds to
@ -2450,46 +2516,45 @@ static void *cgroup_tasks_start(struct seq_file *s, loff_t *pos)
* after a seek to the start). Use a binary-search to find the
* next pid to display, if any
*/
struct cgroup *cgrp = s->private;
struct cgroup_pidlist *l = s->private;
int index = 0, pid = *pos;
int *iter;
down_read(&cgrp->pids_mutex);
down_read(&l->mutex);
if (pid) {
int end = cgrp->pids_length;
int end = l->length;
while (index < end) {
int mid = (index + end) / 2;
if (cgrp->tasks_pids[mid] == pid) {
if (l->list[mid] == pid) {
index = mid;
break;
} else if (cgrp->tasks_pids[mid] <= pid)
} else if (l->list[mid] <= pid)
index = mid + 1;
else
end = mid;
}
}
/* If we're off the end of the array, we're done */
if (index >= cgrp->pids_length)
if (index >= l->length)
return NULL;
/* Update the abstract position to be the actual pid that we found */
iter = cgrp->tasks_pids + index;
iter = l->list + index;
*pos = *iter;
return iter;
}
static void cgroup_tasks_stop(struct seq_file *s, void *v)
static void cgroup_pidlist_stop(struct seq_file *s, void *v)
{
struct cgroup *cgrp = s->private;
up_read(&cgrp->pids_mutex);
struct cgroup_pidlist *l = s->private;
up_read(&l->mutex);
}
static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos)
{
struct cgroup *cgrp = s->private;
int *p = v;
int *end = cgrp->tasks_pids + cgrp->pids_length;
struct cgroup_pidlist *l = s->private;
pid_t *p = v;
pid_t *end = l->list + l->length;
/*
* Advance to the next pid in the array. If this goes off the
* end, we're done
@ -2503,98 +2568,94 @@ static void *cgroup_tasks_next(struct seq_file *s, void *v, loff_t *pos)
}
}
static int cgroup_tasks_show(struct seq_file *s, void *v)
static int cgroup_pidlist_show(struct seq_file *s, void *v)
{
return seq_printf(s, "%d\n", *(int *)v);
}
static const struct seq_operations cgroup_tasks_seq_operations = {
.start = cgroup_tasks_start,
.stop = cgroup_tasks_stop,
.next = cgroup_tasks_next,
.show = cgroup_tasks_show,
/*
* seq_operations functions for iterating on pidlists through seq_file -
* independent of whether it's tasks or procs
*/
static const struct seq_operations cgroup_pidlist_seq_operations = {
.start = cgroup_pidlist_start,
.stop = cgroup_pidlist_stop,
.next = cgroup_pidlist_next,
.show = cgroup_pidlist_show,
};
static void release_cgroup_pid_array(struct cgroup *cgrp)
static void cgroup_release_pid_array(struct cgroup_pidlist *l)
{
down_write(&cgrp->pids_mutex);
BUG_ON(!cgrp->pids_use_count);
if (!--cgrp->pids_use_count) {
kfree(cgrp->tasks_pids);
cgrp->tasks_pids = NULL;
cgrp->pids_length = 0;
down_write(&l->mutex);
BUG_ON(!l->use_count);
if (!--l->use_count) {
kfree(l->list);
l->list = NULL;
l->length = 0;
}
up_write(&cgrp->pids_mutex);
up_write(&l->mutex);
}
static int cgroup_tasks_release(struct inode *inode, struct file *file)
static int cgroup_pidlist_release(struct inode *inode, struct file *file)
{
struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
struct cgroup_pidlist *l;
if (!(file->f_mode & FMODE_READ))
return 0;
release_cgroup_pid_array(cgrp);
/*
* the seq_file will only be initialized if the file was opened for
* reading; hence we check if it's not null only in that case.
*/
l = ((struct seq_file *)file->private_data)->private;
cgroup_release_pid_array(l);
return seq_release(inode, file);
}
static struct file_operations cgroup_tasks_operations = {
static const struct file_operations cgroup_pidlist_operations = {
.read = seq_read,
.llseek = seq_lseek,
.write = cgroup_file_write,
.release = cgroup_tasks_release,
.release = cgroup_pidlist_release,
};
/*
* Handle an open on 'tasks' file. Prepare an array containing the
* process id's of tasks currently attached to the cgroup being opened.
* The following functions handle opens on a file that displays a pidlist
* (tasks or procs). Prepare an array of the process/thread IDs of whoever's
* in the cgroup.
*/
static int cgroup_tasks_open(struct inode *unused, struct file *file)
/* helper function for the two below it */
static int cgroup_pidlist_open(struct file *file, bool procs)
{
struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
pid_t *pidarray;
int npids;
struct cgroup_pidlist *l = (procs ? &cgrp->procs : &cgrp->tasks);
int retval;
/* Nothing to do for write-only files */
if (!(file->f_mode & FMODE_READ))
return 0;
/*
* 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(cgrp);
pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
if (!pidarray)
return -ENOMEM;
npids = pid_array_load(pidarray, npids, cgrp);
sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
/* have the array populated */
retval = pidlist_array_load(cgrp, procs);
if (retval)
return retval;
/* configure file information */
file->f_op = &cgroup_pidlist_operations;
/*
* Store the array in the cgroup, freeing the old
* array if necessary
*/
down_write(&cgrp->pids_mutex);
kfree(cgrp->tasks_pids);
cgrp->tasks_pids = pidarray;
cgrp->pids_length = npids;
cgrp->pids_use_count++;
up_write(&cgrp->pids_mutex);
file->f_op = &cgroup_tasks_operations;
retval = seq_open(file, &cgroup_tasks_seq_operations);
retval = seq_open(file, &cgroup_pidlist_seq_operations);
if (retval) {
release_cgroup_pid_array(cgrp);
cgroup_release_pid_array(l);
return retval;
}
((struct seq_file *)file->private_data)->private = cgrp;
((struct seq_file *)file->private_data)->private = l;
return 0;
}
static int cgroup_tasks_open(struct inode *unused, struct file *file)
{
return cgroup_pidlist_open(file, false);
}
static int cgroup_procs_open(struct inode *unused, struct file *file)
{
return cgroup_pidlist_open(file, true);
}
static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
struct cftype *cft)
@ -2617,21 +2678,27 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp,
/*
* for the common functions, 'private' gives the type of file
*/
/* for hysterical raisins, we can't put this on the older files */
#define CGROUP_FILE_GENERIC_PREFIX "cgroup."
static struct cftype files[] = {
{
.name = "tasks",
.open = cgroup_tasks_open,
.write_u64 = cgroup_tasks_write,
.release = cgroup_tasks_release,
.private = FILE_TASKLIST,
.release = cgroup_pidlist_release,
.mode = S_IRUGO | S_IWUSR,
},
{
.name = CGROUP_FILE_GENERIC_PREFIX "procs",
.open = cgroup_procs_open,
/* .write_u64 = cgroup_procs_write, TODO */
.release = cgroup_pidlist_release,
.mode = S_IRUGO,
},
{
.name = "notify_on_release",
.read_u64 = cgroup_read_notify_on_release,
.write_u64 = cgroup_write_notify_on_release,
.private = FILE_NOTIFY_ON_RELEASE,
},
};
@ -2640,7 +2707,6 @@ static struct cftype cft_release_agent = {
.read_seq_string = cgroup_release_agent_show,
.write_string = cgroup_release_agent_write,
.max_write_len = PATH_MAX,
.private = FILE_RELEASE_AGENT,
};
static int cgroup_populate_dir(struct cgroup *cgrp)