Commit e5991371 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm: remove cgroup_mm_owner_callbacks 



cgroup_mm_owner_callbacks() was brought in to support the memrlimit
controller, but sneaked into mainline ahead of it.  That controller has
now been shelved, and the mm_owner_changed() args were inadequate for it
anyway (they needed an mm pointer instead of a task pointer).

Remove the dead code, and restore mm_update_next_owner() locking to how it
was before: taking mmap_sem there does nothing for memcontrol.c, now the
only user of mm->owner.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 39f0dee2

include/linux/cgroup.h

+1 −13
Original line number Diff line number Diff line
@@ -329,13 +329,7 @@ struct cgroup_subsys { 
			struct cgroup *cgrp);

	void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);

	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);

	/*

	 * This routine is called with the task_lock of mm->owner held

	 */

	void (*mm_owner_changed)(struct cgroup_subsys *ss,

					struct cgroup *old,

					struct cgroup *new,

					struct task_struct *p);



	int subsys_id;

	int active;

	int disabled;
@@ -400,9 +394,6 @@ void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it); 
int cgroup_scan_tasks(struct cgroup_scanner *scan);

int cgroup_attach_task(struct cgroup *, struct task_struct *);



void cgroup_mm_owner_callbacks(struct task_struct *old,

			       struct task_struct *new);



#else /* !CONFIG_CGROUPS */



static inline int cgroup_init_early(void) { return 0; }
@@ -420,9 +411,6 @@ static inline int cgroupstats_build(struct cgroupstats *stats, 
	return -EINVAL;

}



static inline void cgroup_mm_owner_callbacks(struct task_struct *old,

					     struct task_struct *new) {}



#endif /* !CONFIG_CGROUPS */



#endif /* _LINUX_CGROUP_H */

kernel/cgroup.c

+0 −33
Original line number Diff line number Diff line
@@ -116,7 +116,6 @@ static int root_count; 
 * be called.

 */

static int need_forkexit_callback __read_mostly;

static int need_mm_owner_callback __read_mostly;



/* convenient tests for these bits */

inline int cgroup_is_removed(const struct cgroup *cgrp)
@@ -2539,7 +2538,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
	init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];



	need_forkexit_callback |= ss->fork || ss->exit;

	need_mm_owner_callback |= !!ss->mm_owner_changed;



	/* At system boot, before all subsystems have been

	 * registered, no tasks have been forked, so we don't
@@ -2789,37 +2787,6 @@ void cgroup_fork_callbacks(struct task_struct *child) 
	}

}



#ifdef CONFIG_MM_OWNER

/**

 * cgroup_mm_owner_callbacks - run callbacks when the mm->owner changes

 * @p: the new owner

 *

 * Called on every change to mm->owner. mm_init_owner() does not

 * invoke this routine, since it assigns the mm->owner the first time

 * and does not change it.

 *

 * The callbacks are invoked with mmap_sem held in read mode.

 */

void cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)

{

	struct cgroup *oldcgrp, *newcgrp = NULL;



	if (need_mm_owner_callback) {

		int i;

		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = subsys[i];

			oldcgrp = task_cgroup(old, ss->subsys_id);

			if (new)

				newcgrp = task_cgroup(new, ss->subsys_id);

			if (oldcgrp == newcgrp)

				continue;

			if (ss->mm_owner_changed)

				ss->mm_owner_changed(ss, oldcgrp, newcgrp, new);

		}

	}

}

#endif /* CONFIG_MM_OWNER */



/**

 * cgroup_post_fork - called on a new task after adding it to the task list

 * @child: the task in question

kernel/exit.c

+6 −10
Original line number Diff line number Diff line
@@ -642,35 +642,31 @@ retry: 
	/*

	 * We found no owner yet mm_users > 1: this implies that we are

	 * most likely racing with swapoff (try_to_unuse()) or /proc or

	 * ptrace or page migration (get_task_mm()).  Mark owner as NULL,

	 * so that subsystems can understand the callback and take action.

	 * ptrace or page migration (get_task_mm()).  Mark owner as NULL.

	 */

	down_write(&mm->mmap_sem);

	cgroup_mm_owner_callbacks(mm->owner, NULL);

	mm->owner = NULL;

	up_write(&mm->mmap_sem);

	return;



assign_new_owner:

	BUG_ON(c == p);

	get_task_struct(c);

	read_unlock(&tasklist_lock);

	down_write(&mm->mmap_sem);

	/*

	 * The task_lock protects c->mm from changing.

	 * We always want mm->owner->mm == mm

	 */

	task_lock(c);

	/*

	 * Delay read_unlock() till we have the task_lock()

	 * to ensure that c does not slip away underneath us

	 */

	read_unlock(&tasklist_lock);

	if (c->mm != mm) {

		task_unlock(c);

		up_write(&mm->mmap_sem);

		put_task_struct(c);

		goto retry;

	}

	cgroup_mm_owner_callbacks(mm->owner, c);

	mm->owner = c;

	task_unlock(c);

	up_write(&mm->mmap_sem);

	put_task_struct(c);

}

#endif /* CONFIG_MM_OWNER */

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