[PATCH] configfs: Fix failing symlink() making rmdir() fail
On a similar pattern as mkdir() vs rmdir(), a failing symlink() may make rmdir()
fail for the symlink's parent and the symlink's target as well.
failing symlink() making target's rmdir() fail:
process 1: process 2:
symlink("A/S" -> "B")
allow_link()
create_link()
attach to "B" links list
rmdir("B")
detach_prep("B")
error because of new link
configfs_create_link("A", "S")
error (eg -ENOMEM)
failing symlink() making parent's rmdir() fail:
process 1: process 2:
symlink("A/D/S" -> "B")
allow_link()
create_link()
attach to "B" links list
configfs_create_link("A/D", "S")
make_dirent("A/D", "S")
rmdir("A")
detach_prep("A")
detach_prep("A/D")
error because of "S"
create("S")
error (eg -ENOMEM)
We cannot use the same solution as for mkdir() vs rmdir(), since rmdir() on the
target cannot wait on the i_mutex of the new symlink's parent without risking a
deadlock (with other symlink() or sys_rename()). Instead we define a global
mutex protecting all configfs symlinks attachment, so that rmdir() can avoid the
races above.
Signed-off-by: Louis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index da015c1..5f61b26 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -51,6 +51,7 @@
#define CONFIGFS_USET_IN_MKDIR 0x0200
#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR)
+extern struct mutex configfs_symlink_mutex;
extern spinlock_t configfs_dirent_lock;
extern struct vfsmount * configfs_mount;
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index cb5ea44..4e228c8 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1207,6 +1207,11 @@
return -EINVAL;
}
+ /*
+ * Ensure that no racing symlink() will make detach_prep() fail while
+ * the new link is temporarily attached
+ */
+ mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
do {
struct mutex *wait_mutex;
@@ -1215,6 +1220,7 @@
if (ret) {
configfs_detach_rollback(dentry);
spin_unlock(&configfs_dirent_lock);
+ mutex_unlock(&configfs_symlink_mutex);
if (ret != -EAGAIN) {
config_item_put(parent_item);
return ret;
@@ -1224,10 +1230,12 @@
mutex_lock(wait_mutex);
mutex_unlock(wait_mutex);
+ mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
}
} while (ret == -EAGAIN);
spin_unlock(&configfs_dirent_lock);
+ mutex_unlock(&configfs_symlink_mutex);
/* Get a working ref for the duration of this function */
item = configfs_get_config_item(dentry);
@@ -1517,11 +1525,13 @@
mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex,
I_MUTEX_PARENT);
mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
+ mutex_lock(&configfs_symlink_mutex);
spin_lock(&configfs_dirent_lock);
if (configfs_detach_prep(dentry, NULL)) {
printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");
}
spin_unlock(&configfs_dirent_lock);
+ mutex_unlock(&configfs_symlink_mutex);
configfs_detach_group(&group->cg_item);
dentry->d_inode->i_flags |= S_DEAD;
mutex_unlock(&dentry->d_inode->i_mutex);
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index c12801a..61a886d 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -31,6 +31,9 @@
#include <linux/configfs.h>
#include "configfs_internal.h"
+/* Protects attachments of new symlinks */
+DEFINE_MUTEX(configfs_symlink_mutex);
+
static int item_depth(struct config_item * item)
{
struct config_item * p = item;
@@ -147,7 +150,9 @@
ret = type->ct_item_ops->allow_link(parent_item, target_item);
if (!ret) {
+ mutex_lock(&configfs_symlink_mutex);
ret = create_link(parent_item, target_item, dentry);
+ mutex_unlock(&configfs_symlink_mutex);
if (ret && type->ct_item_ops->drop_link)
type->ct_item_ops->drop_link(parent_item,
target_item);