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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: Hugh Dickins <hugh@veritas.com>
Cc: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-01-06 14:39:22 -08:00 committed by Linus Torvalds
parent 39f0dee2d8
commit e5991371ee
3 changed files with 7 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/linux/cgroup.h
View File

@ -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 */

33
kernel/cgroup.c
View File

@ -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

16
kernel/exit.c
View File

@ -642,35 +642,31 @@ void mm_update_next_owner(struct mm_struct *mm)
/*
* 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 */