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Commit 6f610764 authored by Louis Rilling's avatar Louis Rilling Committed by Mark Fasheh
Browse files

configfs: Introduce configfs_dirent_lock 



This patch introduces configfs_dirent_lock spinlock to protect configfs_dirent
traversals against linkage mutations (add/del/move). This will allow
configfs_detach_prep() to avoid locking i_mutexes.

Locking rules for configfs_dirent linkage mutations are the same plus the
requirement of taking configfs_dirent_lock. For configfs_dirent walking, one can
either take appropriate i_mutex as before, or take configfs_dirent_lock.

The spinlock could actually be a mutex, but the critical sections are either
O(1) or should not be too long (default groups walking in last patch).

ChangeLog:
  - Clarify the comment on configfs_dirent_lock usage
  - Move sd->s_element init before linking the new dirent
  - In lseek(), do not release configfs_dirent_lock before the dirent is
    relinked.

Signed-off-by: default avatarLouis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
parent fe9f3877

fs/configfs/configfs_internal.h

+3 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 


#include <linux/slab.h>

#include <linux/list.h>

#include <linux/spinlock.h>



struct configfs_dirent {

	atomic_t		s_count;
@@ -49,6 +50,8 @@ struct configfs_dirent { 
#define CONFIGFS_USET_DROPPING	0x0100

#define CONFIGFS_NOT_PINNED	(CONFIGFS_ITEM_ATTR)



extern spinlock_t configfs_dirent_lock;



extern struct vfsmount * configfs_mount;

extern struct kmem_cache *configfs_dir_cachep;

fs/configfs/dir.c

+27 −1
Original line number Diff line number Diff line
@@ -35,6 +35,14 @@ 
#include "configfs_internal.h"



DECLARE_RWSEM(configfs_rename_sem);

/*

 * Protects mutations of configfs_dirent linkage together with proper i_mutex

 * Mutators of configfs_dirent linkage must *both* have the proper inode locked

 * and configfs_dirent_lock locked, in that order.

 * This allows one to safely traverse configfs_dirent trees without having to

 * lock inodes.

 */

DEFINE_SPINLOCK(configfs_dirent_lock);



static void configfs_d_iput(struct dentry * dentry,

			    struct inode * inode)
@@ -79,8 +87,10 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare 
	atomic_set(&sd->s_count, 1);

	INIT_LIST_HEAD(&sd->s_links);

	INIT_LIST_HEAD(&sd->s_children);

	list_add(&sd->s_sibling, &parent_sd->s_children);

	sd->s_element = element;

	spin_lock(&configfs_dirent_lock);

	list_add(&sd->s_sibling, &parent_sd->s_children);

	spin_unlock(&configfs_dirent_lock);



	return sd;

}
@@ -173,7 +183,9 @@ static int create_dir(struct config_item * k, struct dentry * p, 
		} else {

			struct configfs_dirent *sd = d->d_fsdata;

			if (sd) {

				spin_lock(&configfs_dirent_lock);

				list_del_init(&sd->s_sibling);

				spin_unlock(&configfs_dirent_lock);

				configfs_put(sd);

			}

		}
@@ -224,7 +236,9 @@ int configfs_create_link(struct configfs_symlink *sl, 
		else {

			struct configfs_dirent *sd = dentry->d_fsdata;

			if (sd) {

				spin_lock(&configfs_dirent_lock);

				list_del_init(&sd->s_sibling);

				spin_unlock(&configfs_dirent_lock);

				configfs_put(sd);

			}

		}
@@ -238,7 +252,9 @@ static void remove_dir(struct dentry * d) 
	struct configfs_dirent * sd;



	sd = d->d_fsdata;

	spin_lock(&configfs_dirent_lock);

	list_del_init(&sd->s_sibling);

	spin_unlock(&configfs_dirent_lock);

	configfs_put(sd);

	if (d->d_inode)

		simple_rmdir(parent->d_inode,d);
@@ -410,7 +426,9 @@ static void detach_attrs(struct config_item * item) 
	list_for_each_entry_safe(sd, tmp, &parent_sd->s_children, s_sibling) {

		if (!sd->s_element || !(sd->s_type & CONFIGFS_NOT_PINNED))

			continue;

		spin_lock(&configfs_dirent_lock);

		list_del_init(&sd->s_sibling);

		spin_unlock(&configfs_dirent_lock);

		configfs_drop_dentry(sd, dentry);

		configfs_put(sd);

	}
@@ -1268,7 +1286,9 @@ static int configfs_dir_close(struct inode *inode, struct file *file) 
	struct configfs_dirent * cursor = file->private_data;



	mutex_lock(&dentry->d_inode->i_mutex);

	spin_lock(&configfs_dirent_lock);

	list_del_init(&cursor->s_sibling);

	spin_unlock(&configfs_dirent_lock);

	mutex_unlock(&dentry->d_inode->i_mutex);



	release_configfs_dirent(cursor);
@@ -1308,7 +1328,9 @@ static int configfs_readdir(struct file * filp, void * dirent, filldir_t filldir 
			/* fallthrough */

		default:

			if (filp->f_pos == 2) {

				spin_lock(&configfs_dirent_lock);

				list_move(q, &parent_sd->s_children);

				spin_unlock(&configfs_dirent_lock);

			}

			for (p=q->next; p!= &parent_sd->s_children; p=p->next) {

				struct configfs_dirent *next;
@@ -1331,7 +1353,9 @@ static int configfs_readdir(struct file * filp, void * dirent, filldir_t filldir 
						 dt_type(next)) < 0)

					return 0;



				spin_lock(&configfs_dirent_lock);

				list_move(q, p);

				spin_unlock(&configfs_dirent_lock);

				p = q;

				filp->f_pos++;

			}
@@ -1362,6 +1386,7 @@ static loff_t configfs_dir_lseek(struct file * file, loff_t offset, int origin) 
			struct list_head *p;

			loff_t n = file->f_pos - 2;



			spin_lock(&configfs_dirent_lock);

			list_del(&cursor->s_sibling);

			p = sd->s_children.next;

			while (n && p != &sd->s_children) {
@@ -1373,6 +1398,7 @@ static loff_t configfs_dir_lseek(struct file * file, loff_t offset, int origin) 
				p = p->next;

			}

			list_add_tail(&cursor->s_sibling, p);

			spin_unlock(&configfs_dirent_lock);

		}

	}

	mutex_unlock(&dentry->d_inode->i_mutex);

fs/configfs/inode.c

+2 −0
Original line number Diff line number Diff line
@@ -247,7 +247,9 @@ void configfs_hash_and_remove(struct dentry * dir, const char * name) 
		if (!sd->s_element)

			continue;

		if (!strcmp(configfs_get_name(sd), name)) {

			spin_lock(&configfs_dirent_lock);

			list_del_init(&sd->s_sibling);

			spin_unlock(&configfs_dirent_lock);

			configfs_drop_dentry(sd, dir);

			configfs_put(sd);

			break;

fs/configfs/symlink.c

+2 −0
Original line number Diff line number Diff line
@@ -169,7 +169,9 @@ int configfs_unlink(struct inode *dir, struct dentry *dentry) 
	parent_item = configfs_get_config_item(dentry->d_parent);

	type = parent_item->ci_type;



	spin_lock(&configfs_dirent_lock);

	list_del_init(&sd->s_sibling);

	spin_unlock(&configfs_dirent_lock);

	configfs_drop_dentry(sd, dentry->d_parent);

	dput(dentry);

	configfs_put(sd);