From: Louis Rilling <[EMAIL PROTECTED]>
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 <[EMAIL PROTECTED]>
Signed-off-by: Joel Becker <[EMAIL PROTECTED]>
---
fs/configfs/configfs_internal.h | 1 +
fs/configfs/dir.c | 53 +++++++++++++++++++++++++++++++-------
2 files changed, 44 insertions(+), 10 deletions(-)
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index 5a33b58..da015c1 100644
--- a/fs/configfs/configfs_internal.h
+++ b/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;
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index d5b5985..614e382 100644
--- a/fs/configfs/dir.c
+++ b/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);
--
1.5.4.1
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