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cgroup files: move the release_agent file to use typed handlers 

Adds cgroup_release_agent_write() and cgroup_release_agent_show()
methods to handle writing/reading the path to a cgroup hierarchy's
release agent. As a result, cgroup_common_file_read() is now unnecessary.

As part of the change, a previously-tolerated race in
cgroup_release_agent() is avoided by copying the current
release_agent_path prior to calling call_usermode_helper().

Signed-off-by: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul Menage 2008-07-25 01:46:59 -07:00 committed by Linus Torvalds
parent db3b14978a
commit e788e066c6
2 changed files with 59 additions and 68 deletions
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2
include/linux/cgroup.h
View File

@ -295,6 +295,8 @@ int cgroup_add_files(struct cgroup *cgrp,
int cgroup_is_removed(const struct cgroup *cgrp);
int cgroup_lock_live_group(struct cgroup *cgrp);
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
int cgroup_task_count(const struct cgroup *cgrp);

125
kernel/cgroup.c
View File

@ -89,11 +89,7 @@ struct cgroupfs_root {
/* Hierarchy-specific flags */
unsigned long flags;
/* The path to use for release notifications. No locking
* between setting and use - so if userspace updates this
* while child cgroups exist, you could miss a
* notification. We ensure that it's always a valid
* NUL-terminated string */
/* The path to use for release notifications. */
char release_agent_path[PATH_MAX];
};
@ -1329,6 +1325,45 @@ enum cgroup_filetype {
FILE_RELEASE_AGENT,
};
/**
* cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
* @cgrp: the cgroup to be checked for liveness
*
* Returns true (with lock held) on success, or false (with no lock
* held) on failure.
*/
int cgroup_lock_live_group(struct cgroup *cgrp)
{
mutex_lock(&cgroup_mutex);
if (cgroup_is_removed(cgrp)) {
mutex_unlock(&cgroup_mutex);
return false;
}
return true;
}
static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
const char *buffer)
{
BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;
strcpy(cgrp->root->release_agent_path, buffer);
mutex_unlock(&cgroup_mutex);
return 0;
}
static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
struct seq_file *seq)
{
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;
seq_puts(seq, cgrp->root->release_agent_path);
seq_putc(seq, '\n');
mutex_unlock(&cgroup_mutex);
return 0;
}
static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
const char __user *userbuf,
@ -1443,10 +1478,6 @@ static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
else
clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
break;
case FILE_RELEASE_AGENT:
BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
strcpy(cgrp->root->release_agent_path, buffer);
break;
default:
retval = -EINVAL;
goto out2;
@ -1506,49 +1537,6 @@ static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}
static ssize_t cgroup_common_file_read(struct cgroup *cgrp,
struct cftype *cft,
struct file *file,
char __user *buf,
size_t nbytes, loff_t *ppos)
{
enum cgroup_filetype type = cft->private;
char *page;
ssize_t retval = 0;
char *s;
if (!(page = (char *)__get_free_page(GFP_KERNEL)))
return -ENOMEM;
s = page;
switch (type) {
case FILE_RELEASE_AGENT:
{
struct cgroupfs_root *root;
size_t n;
mutex_lock(&cgroup_mutex);
root = cgrp->root;
n = strnlen(root->release_agent_path,
sizeof(root->release_agent_path));
n = min(n, (size_t) PAGE_SIZE);
strncpy(s, root->release_agent_path, n);
mutex_unlock(&cgroup_mutex);
s += n;
break;
}
default:
retval = -EINVAL;
goto out;
}
*s++ = '\n';
retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
out:
free_page((unsigned long)page);
return retval;
}
static ssize_t cgroup_file_read(struct file *file, char __user *buf,
size_t nbytes, loff_t *ppos)
{
@ -1606,6 +1594,7 @@ int cgroup_seqfile_release(struct inode *inode, struct file *file)
static struct file_operations cgroup_seqfile_operations = {
.read = seq_read,
.write = cgroup_file_write,
.llseek = seq_lseek,
.release = cgroup_seqfile_release,
};
@ -2283,8 +2272,9 @@ static struct cftype files[] = {
static struct cftype cft_release_agent = {
.name = "release_agent",
.read = cgroup_common_file_read,
.write = cgroup_common_file_write,
.read_seq_string = cgroup_release_agent_show,
.write_string = cgroup_release_agent_write,
.max_write_len = PATH_MAX,
.private = FILE_RELEASE_AGENT,
};
@ -3111,27 +3101,24 @@ static void cgroup_release_agent(struct work_struct *work)
while (!list_empty(&release_list)) {
char *argv[3], *envp[3];
int i;
char *pathbuf;
char *pathbuf = NULL, *agentbuf = NULL;
struct cgroup *cgrp = list_entry(release_list.next,
struct cgroup,
release_list);
list_del_init(&cgrp->release_list);
spin_unlock(&release_list_lock);
pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!pathbuf) {
spin_lock(&release_list_lock);
continue;
}
if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) {
kfree(pathbuf);
spin_lock(&release_list_lock);
continue;
}
if (!pathbuf)
goto continue_free;
if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
goto continue_free;
agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
if (!agentbuf)
goto continue_free;
i = 0;
argv[i++] = cgrp->root->release_agent_path;
argv[i++] = (char *)pathbuf;
argv[i++] = agentbuf;
argv[i++] = pathbuf;
argv[i] = NULL;
i = 0;
@ -3145,8 +3132,10 @@ static void cgroup_release_agent(struct work_struct *work)
* be a slow process */
mutex_unlock(&cgroup_mutex);
call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
kfree(pathbuf);
mutex_lock(&cgroup_mutex);
continue_free:
kfree(pathbuf);
kfree(agentbuf);
spin_lock(&release_list_lock);
}
spin_unlock(&release_list_lock);