Commit 8dc4f3e1 authored by Paul Menage's avatar Paul Menage Committed by Linus Torvalds
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cgroups: move cgroups destroy() callbacks to cgroup_diput() 



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: default avatarPaul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 622d42ca

Documentation/cgroups.txt

+11 −11
Original line number Diff line number Diff line
@@ -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

kernel/cgroup.c

+24 −12
Original line number Diff line number Diff line
@@ -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;

}

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