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configfs: Fix failing mkdir() making racing rmdir() fail

When fixing the rename() vs rmdir() deadlock, we stopped locking default groups'
inodes in configfs_detach_prep(), letting racing mkdir() in default groups
proceed concurrently. This enables races like below happen, which leads to a
failing mkdir() making rmdir() fail, despite the group to remove having no
user-created directory under it in the end.

	process A: 			process B:
	/* PWD=A/B */
	mkdir("C")
	  make_item("C")
	  attach_group("C")
					rmdir("A")
					  detach_prep("A")
					    detach_prep("B")
					      error because of "C"
					  return -ENOTEMPTY
	    attach_group("C/D")
	      error (eg -ENOMEM)
	  return -ENOMEM

This patch prevents such scenarii by making rmdir() wait as long as
detach_prep() fails because a racing mkdir() is in the middle of attach_group().
To achieve this, mkdir() sets a flag CONFIGFS_USET_IN_MKDIR in parent's
configfs_dirent before calling attach_group(), and clears the flag once
attach_group() is done. detach_prep() fails with -EAGAIN whenever the flag is
hit and returns the guilty inode's mutex so that rmdir() can wait on it.

Signed-off-by: Louis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
master
Louis Rilling 14 years ago
committed by Mark Fasheh
parent
commit
6d8344baee
  1. 1
      fs/configfs/configfs_internal.h
  2. 53
      fs/configfs/dir.c

1
fs/configfs/configfs_internal.h

@ -48,6 +48,7 @@ struct configfs_dirent {
#define CONFIGFS_USET_DIR 0x0040
#define CONFIGFS_USET_DEFAULT 0x0080
#define CONFIGFS_USET_DROPPING 0x0100
#define CONFIGFS_USET_IN_MKDIR 0x0200
#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR)
extern spinlock_t configfs_dirent_lock;

53
fs/configfs/dir.c

@ -364,7 +364,7 @@ static struct dentry * configfs_lookup(struct inode *dir,
* If there is an error, the caller will reset the flags via
* configfs_detach_rollback().
*/
static int configfs_detach_prep(struct dentry *dentry)
static int configfs_detach_prep(struct dentry *dentry, struct mutex **wait_mutex)
{
struct configfs_dirent *parent_sd = dentry->d_fsdata;
struct configfs_dirent *sd;
@ -379,6 +379,12 @@ static int configfs_detach_prep(struct dentry *dentry)
if (sd->s_type & CONFIGFS_NOT_PINNED)
continue;
if (sd->s_type & CONFIGFS_USET_DEFAULT) {
/* Abort if racing with mkdir() */
if (sd->s_type & CONFIGFS_USET_IN_MKDIR) {
if (wait_mutex)
*wait_mutex = &sd->s_dentry->d_inode->i_mutex;
return -EAGAIN;
}
/* Mark that we're trying to drop the group */
sd->s_type |= CONFIGFS_USET_DROPPING;
@ -386,7 +392,7 @@ static int configfs_detach_prep(struct dentry *dentry)
* Yup, recursive. If there's a problem, blame
* deep nesting of default_groups
*/
ret = configfs_detach_prep(sd->s_dentry);
ret = configfs_detach_prep(sd->s_dentry, wait_mutex);
if (!ret)
continue;
} else
@ -1113,11 +1119,26 @@ static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
*/
module_got = 1;
/*
* Make racing rmdir() fail if it did not tag parent with
* CONFIGFS_USET_DROPPING
* Note: if CONFIGFS_USET_DROPPING is already set, attach_group() will
* fail and let rmdir() terminate correctly
*/
spin_lock(&configfs_dirent_lock);
/* This will make configfs_detach_prep() fail */
sd->s_type |= CONFIGFS_USET_IN_MKDIR;
spin_unlock(&configfs_dirent_lock);
if (group)
ret = configfs_attach_group(parent_item, item, dentry);
else
ret = configfs_attach_item(parent_item, item, dentry);
spin_lock(&configfs_dirent_lock);
sd->s_type &= ~CONFIGFS_USET_IN_MKDIR;
spin_unlock(&configfs_dirent_lock);
out_unlink:
if (ret) {
/* Tear down everything we built up */
@ -1182,13 +1203,25 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
}
spin_lock(&configfs_dirent_lock);
ret = configfs_detach_prep(dentry);
if (ret) {
configfs_detach_rollback(dentry);
spin_unlock(&configfs_dirent_lock);
config_item_put(parent_item);
return ret;
}
do {
struct mutex *wait_mutex;
ret = configfs_detach_prep(dentry, &wait_mutex);
if (ret) {
configfs_detach_rollback(dentry);
spin_unlock(&configfs_dirent_lock);
if (ret != -EAGAIN) {
config_item_put(parent_item);
return ret;
}
/* Wait until the racing operation terminates */
mutex_lock(wait_mutex);
mutex_unlock(wait_mutex);
spin_lock(&configfs_dirent_lock);
}
} while (ret == -EAGAIN);
spin_unlock(&configfs_dirent_lock);
/* Get a working ref for the duration of this function */
@ -1480,7 +1513,7 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys)
I_MUTEX_PARENT);
mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);
spin_lock(&configfs_dirent_lock);
if (configfs_detach_prep(dentry)) {
if (configfs_detach_prep(dentry, NULL)) {
printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");
}
spin_unlock(&configfs_dirent_lock);

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