Commit 87da1493 authored by Greg Kroah-Hartman's avatar Greg Kroah-Hartman
Browse files

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



This reverts commit ea1c472d.

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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0890147f

fs/kernfs/dir.c

+16 −11
Original line number Diff line number Diff line
@@ -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;



	rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);

	kn->u.completion = (void *)&wait;



	atomic_add(KN_DEACTIVATED_BIAS, &kn->active);

	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);



	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;

}

include/linux/kernfs.h

+2 −2
Original line number Diff line number Diff line
@@ -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 {

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