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cgroups: move cgroups destroy() callbacks to cgroup_diput()

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Move the calls to the cgroup subsystem destroy() methods from
cgroup_rmdir() to cgroup_diput().  This allows control file reads and
writes to access their subsystem state without having to be concerned with
locking against cgroup destruction - the control file dentry will keep the
cgroup and its subsystem state objects alive until the file is closed.

The documentation is updated to reflect the changed semantics of destroy();
additionally the locking comments for destroy() and some other methods were
clarified and decrustified.

Signed-off-by: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.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 2008-02-07 00:13:45 -08:00 committed by Linus Torvalds
parent 622d42cac9
commit 8dc4f3e17d
2 changed files with 35 additions and 23 deletions
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22
Documentation/cgroups.txt
View file

@ -456,7 +456,7 @@ methods are create/destroy. Any others that are null are presumed to
be successful no-ops.
struct cgroup_subsys_state *create(struct cgroup *cont)
LL=cgroup_mutex
(cgroup_mutex held by caller)
Called to create a subsystem state object for a cgroup. The
subsystem should allocate its subsystem state object for the passed
@ -471,14 +471,19 @@ it's the root of the hierarchy) and may be an appropriate place for
initialization code.
void destroy(struct cgroup *cont)
LL=cgroup_mutex
(cgroup_mutex held by caller)
The cgroup system is about to destroy the passed cgroup; the
subsystem should do any necessary cleanup
The cgroup system is about to destroy the passed cgroup; the subsystem
should do any necessary cleanup and free its subsystem state
object. By the time this method is called, the cgroup has already been
unlinked from the file system and from the child list of its parent;
cgroup->parent is still valid. (Note - can also be called for a
newly-created cgroup if an error occurs after this subsystem's
create() method has been called for the new cgroup).
int can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
struct task_struct *task)
LL=cgroup_mutex
(cgroup_mutex held by caller)
Called prior to moving a task into a cgroup; if the subsystem
returns an error, this will abort the attach operation. If a NULL
@ -489,25 +494,20 @@ remain valid while the caller holds cgroup_mutex.
void attach(struct cgroup_subsys *ss, struct cgroup *cont,
struct cgroup *old_cont, struct task_struct *task)
LL=cgroup_mutex
Called after the task has been attached to the cgroup, to allow any
post-attachment activity that requires memory allocations or blocking.
void fork(struct cgroup_subsy *ss, struct task_struct *task)
LL=callback_mutex, maybe read_lock(tasklist_lock)
Called when a task is forked into a cgroup. Also called during
registration for all existing tasks.
void exit(struct cgroup_subsys *ss, struct task_struct *task)
LL=callback_mutex
Called during task exit
int populate(struct cgroup_subsys *ss, struct cgroup *cont)
LL=none
Called after creation of a cgroup to allow a subsystem to populate
the cgroup directory with file entries. The subsystem should make
@ -524,7 +524,7 @@ example in cpusets, no task may attach before 'cpus' and 'mems' are set
up.
void bind(struct cgroup_subsys *ss, struct cgroup *root)
LL=callback_mutex
(cgroup_mutex held by caller)
Called when a cgroup subsystem is rebound to a different hierarchy
and root cgroup. Currently this will only involve movement between

36
kernel/cgroup.c
View file

@ -591,6 +591,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
/* is dentry a directory ? if so, kfree() associated cgroup */
if (S_ISDIR(inode->i_mode)) {
struct cgroup *cgrp = dentry->d_fsdata;
struct cgroup_subsys *ss;
BUG_ON(!(cgroup_is_removed(cgrp)));
/* It's possible for external users to be holding css
* reference counts on a cgroup; css_put() needs to
@ -599,6 +600,23 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
* queue the cgroup to be handled by the release
* agent */
synchronize_rcu();
mutex_lock(&cgroup_mutex);
/*
* Release the subsystem state objects.
*/
for_each_subsys(cgrp->root, ss) {
if (cgrp->subsys[ss->subsys_id])
ss->destroy(ss, cgrp);
}
cgrp->root->number_of_cgroups--;
mutex_unlock(&cgroup_mutex);
/* Drop the active superblock reference that we took when we
* created the cgroup */
deactivate_super(cgrp->root->sb);
kfree(cgrp);
}
iput(inode);
@ -1330,6 +1348,10 @@ static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
mutex_lock(&cgroup_mutex);
/*
* This was already checked for in cgroup_file_write(), but
* check again now we're holding cgroup_mutex.
*/
if (cgroup_is_removed(cgrp)) {
retval = -ENODEV;
goto out2;
@ -1370,7 +1392,7 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
struct cftype *cft = __d_cft(file->f_dentry);
struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
if (!cft)
if (!cft || cgroup_is_removed(cgrp))
return -ENODEV;
if (cft->write)
return cft->write(cgrp, cft, file, buf, nbytes, ppos);
@ -1440,7 +1462,7 @@ static ssize_t cgroup_file_read(struct file *file, char __user *buf,
struct cftype *cft = __d_cft(file->f_dentry);
struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
if (!cft)
if (!cft || cgroup_is_removed(cgrp))
return -ENODEV;
if (cft->read)
@ -2120,7 +2142,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
struct cgroup *cgrp = dentry->d_fsdata;
struct dentry *d;
struct cgroup *parent;
struct cgroup_subsys *ss;
struct super_block *sb;
struct cgroupfs_root *root;
@ -2145,11 +2166,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
return -EBUSY;
}
for_each_subsys(root, ss) {
if (cgrp->subsys[ss->subsys_id])
ss->destroy(ss, cgrp);
}
spin_lock(&release_list_lock);
set_bit(CGRP_REMOVED, &cgrp->flags);
if (!list_empty(&cgrp->release_list))
@ -2164,15 +2180,11 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
cgroup_d_remove_dir(d);
dput(d);
root->number_of_cgroups--;
set_bit(CGRP_RELEASABLE, &parent->flags);
check_for_release(parent);
mutex_unlock(&cgroup_mutex);
/* Drop the active superblock reference that we took when we
* created the cgroup */
deactivate_super(sb);
return 0;
}