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Subject[PATCH 10/17] configfs: Introduce configfs_dirent_lock
Date
From: Louis Rilling <Louis.Rilling@kerlabs.com>

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: Louis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
---
fs/configfs/configfs_internal.h | 3 +++
fs/configfs/dir.c | 28 +++++++++++++++++++++++++++-
fs/configfs/inode.c | 2 ++
fs/configfs/symlink.c | 2 ++
4 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index cca9860..5a33b58 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -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;

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index a48dc7d..2619f48 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -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);
diff --git a/fs/configfs/inode.c b/fs/configfs/inode.c
index b9a1d81..4803ccc 100644
--- a/fs/configfs/inode.c
+++ b/fs/configfs/inode.c
@@ -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;
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index 2a731ef..676c84c 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -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);
--
1.5.4.1


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