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Revert "kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq"

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This reverts commit ea1c472dfe.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Greg Kroah-Hartman 2014-01-13 14:43:11 -08:00
parent 0890147fe0
commit 87da149343
2 changed files with 18 additions and 13 deletions
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27
fs/kernfs/dir.c
View file

@ -8,7 +8,6 @@
* This file is released under the GPLv2.
*/
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/idr.h>
@ -152,7 +151,6 @@ struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
*/
void kernfs_put_active(struct kernfs_node *kn)
{
struct kernfs_root *root = kernfs_root(kn);
int v;
if (unlikely(!kn))
@ -164,7 +162,11 @@ void kernfs_put_active(struct kernfs_node *kn)
if (likely(v != KN_DEACTIVATED_BIAS))
return;
wake_up_all(&root->deactivate_waitq);
/*
* atomic_dec_return() is a mb(), we'll always see the updated
* kn->u.completion.
*/
complete(kn->u.completion);
}
/**
@ -175,22 +177,26 @@ void kernfs_put_active(struct kernfs_node *kn)
*/
static void kernfs_deactivate(struct kernfs_node *kn)
{
struct kernfs_root *root = kernfs_root(kn);
DECLARE_COMPLETION_ONSTACK(wait);
int v;
BUG_ON(!(kn->flags & KERNFS_REMOVED));
if (!(kernfs_type(kn) & KERNFS_ACTIVE_REF))
return;
kn->u.completion = (void *)&wait;
rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
/* atomic_add_return() is a mb(), put_active() will always see
* the updated kn->u.completion.
*/
v = atomic_add_return(KN_DEACTIVATED_BIAS, &kn->active);
atomic_add(KN_DEACTIVATED_BIAS, &kn->active);
if (atomic_read(&kn->active) != KN_DEACTIVATED_BIAS)
if (v != KN_DEACTIVATED_BIAS) {
lock_contended(&kn->dep_map, _RET_IP_);
wait_event(root->deactivate_waitq,
atomic_read(&kn->active) == KN_DEACTIVATED_BIAS);
wait_for_completion(&wait);
}
lock_acquired(&kn->dep_map, _RET_IP_);
rwsem_release(&kn->dep_map, 1, _RET_IP_);
@ -607,7 +613,6 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
root->dir_ops = kdops;
root->kn = kn;
init_waitqueue_head(&root->deactivate_waitq);
return root;
}

4
include/linux/kernfs.h
View file

@ -15,7 +15,7 @@
#include <linux/lockdep.h>
#include <linux/rbtree.h>
#include <linux/atomic.h>
#include <linux/wait.h>
#include <linux/completion.h>
struct file;
struct iattr;
@ -91,6 +91,7 @@ struct kernfs_node {
struct rb_node rb;
union {
struct completion *completion;
struct kernfs_node *removed_list;
} u;
@ -131,7 +132,6 @@ struct kernfs_root {
/* private fields, do not use outside kernfs proper */
struct ida ino_ida;
struct kernfs_dir_ops *dir_ops;
wait_queue_head_t deactivate_waitq;
};
struct kernfs_open_file {