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ovl: take lower dir inode mutex outside upper sb_writers lock 

The functions ovl_lower_positive() and ovl_check_empty_dir() both take
inode mutex on the real lower dir under ovl_want_write() which takes
the upper_mnt sb_writers lock.

While this is not a clear locking order or layering violation, it creates
an undesired lock dependency between two unrelated layers for no good
reason.

This lock dependency materializes to a false(?) positive lockdep warning
when calling rmdir() on a nested overlayfs, where both nested and
underlying overlayfs both use the same fs type as upper layer.

rmdir() on the nested overlayfs creates the lock chain:
  sb_writers of upper_mnt (e.g. tmpfs) in ovl_do_remove()
  ovl_i_mutex_dir_key[] of lower overlay dir in ovl_lower_positive()

rmdir() on the underlying overlayfs creates the lock chain in
reverse order:
  ovl_i_mutex_dir_key[] of lower overlay dir in vfs_rmdir()
  sb_writers of nested upper_mnt (e.g. tmpfs) in ovl_do_remove()

To rid of the unneeded locking dependency, move both ovl_lower_positive()
and ovl_check_empty_dir() to before ovl_want_write() in rmdir() and
rename() implementation.

This change spreads the pieces of ovl_check_empty_and_clear() directly
inside the rmdir()/rename() implementations so the helper is no longer
needed and removed.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2017-11-10 13:18:07 +02:00 committed by Miklos Szeredi
parent d796e77f1d
commit 6d0a8a90a5
3 changed files with 58 additions and 65 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

117
fs/overlayfs/dir.c
View File

@ -181,11 +181,6 @@ static bool ovl_type_origin(struct dentry *dentry)
return OVL_TYPE_ORIGIN(ovl_path_type(dentry));
}
static bool ovl_may_have_whiteouts(struct dentry *dentry)
{
return ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
}
static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
struct cattr *attr, struct dentry *hardlink)
{
@ -301,37 +296,6 @@ static struct dentry *ovl_clear_empty(struct dentry *dentry,
return ERR_PTR(err);
}
static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry)
{
int err;
struct dentry *ret = NULL;
LIST_HEAD(list);
err = ovl_check_empty_dir(dentry, &list);
if (err) {
ret = ERR_PTR(err);
goto out_free;
}
/*
* When removing an empty opaque directory, then it makes no sense to
* replace it with an exact replica of itself.
*
* If upperdentry has whiteouts, clear them.
*
* Can race with copy-up, since we don't hold the upperdir mutex.
* Doesn't matter, since copy-up can't create a non-empty directory
* from an empty one.
*/
if (!list_empty(&list))
ret = ovl_clear_empty(dentry, &list);
out_free:
ovl_cache_free(&list);
return ret;
}
static int ovl_set_upper_acl(struct dentry *upperdentry, const char *name,
const struct posix_acl *acl)
{
@ -623,7 +587,8 @@ static bool ovl_matches_upper(struct dentry *dentry, struct dentry *upper)
return d_inode(ovl_dentry_upper(dentry)) == d_inode(upper);
}
static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
static int ovl_remove_and_whiteout(struct dentry *dentry,
struct list_head *list)
{
struct dentry *workdir = ovl_workdir(dentry);
struct inode *wdir = workdir->d_inode;
@ -638,8 +603,8 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
if (WARN_ON(!workdir))
return -EROFS;
if (is_dir) {
opaquedir = ovl_check_empty_and_clear(dentry);
if (!list_empty(list)) {
opaquedir = ovl_clear_empty(dentry, list);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir))
goto out;
@ -694,7 +659,8 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
goto out_d_drop;
}
static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
static int ovl_remove_upper(struct dentry *dentry, bool is_dir,
struct list_head *list)
{
struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
struct inode *dir = upperdir->d_inode;
@ -702,10 +668,8 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
struct dentry *opaquedir = NULL;
int err;
/* Redirect/origin dir can be !ovl_lower_positive && not clean */
if (is_dir && (ovl_dentry_get_redirect(dentry) ||
ovl_may_have_whiteouts(dentry))) {
opaquedir = ovl_check_empty_and_clear(dentry);
if (!list_empty(list)) {
opaquedir = ovl_clear_empty(dentry, list);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir))
goto out;
@ -746,11 +710,26 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
return err;
}
static bool ovl_pure_upper(struct dentry *dentry)
{
return !ovl_dentry_lower(dentry) &&
!ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry));
}
static int ovl_do_remove(struct dentry *dentry, bool is_dir)
{
int err;
bool locked = false;
const struct cred *old_cred;
bool lower_positive = ovl_lower_positive(dentry);
LIST_HEAD(list);
/* No need to clean pure upper removed by vfs_rmdir() */
if (is_dir && (lower_positive || !ovl_pure_upper(dentry))) {
err = ovl_check_empty_dir(dentry, &list);
if (err)
goto out;
}
err = ovl_want_write(dentry);
if (err)
@ -765,10 +744,10 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
goto out_drop_write;
old_cred = ovl_override_creds(dentry->d_sb);
if (!ovl_lower_positive(dentry))
err = ovl_remove_upper(dentry, is_dir);
if (!lower_positive)
err = ovl_remove_upper(dentry, is_dir, &list);
else
err = ovl_remove_and_whiteout(dentry, is_dir);
err = ovl_remove_and_whiteout(dentry, &list);
revert_creds(old_cred);
if (!err) {
if (is_dir)
@ -780,6 +759,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
out_drop_write:
ovl_drop_write(dentry);
out:
ovl_cache_free(&list);
return err;
}
@ -915,6 +895,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
bool samedir = olddir == newdir;
struct dentry *opaquedir = NULL;
const struct cred *old_cred = NULL;
LIST_HEAD(list);
err = -EINVAL;
if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE))
@ -929,6 +910,27 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
if (!overwrite && !ovl_can_move(new))
goto out;
if (overwrite && new_is_dir && !ovl_pure_upper(new)) {
err = ovl_check_empty_dir(new, &list);
if (err)
goto out;
}
if (overwrite) {
if (ovl_lower_positive(old)) {
if (!ovl_dentry_is_whiteout(new)) {
/* Whiteout source */
flags |= RENAME_WHITEOUT;
} else {
/* Switch whiteouts */
flags |= RENAME_EXCHANGE;
}
} else if (is_dir && ovl_dentry_is_whiteout(new)) {
flags |= RENAME_EXCHANGE;
cleanup_whiteout = true;
}
}
err = ovl_want_write(old);
if (err)
goto out;
@ -952,9 +954,8 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
old_cred = ovl_override_creds(old->d_sb);
if (overwrite && new_is_dir && (ovl_type_merge_or_lower(new) ||
ovl_may_have_whiteouts(new))) {
opaquedir = ovl_check_empty_and_clear(new);
if (!list_empty(&list)) {
opaquedir = ovl_clear_empty(new, &list);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir)) {
opaquedir = NULL;
@ -962,21 +963,6 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
}
}
if (overwrite) {
if (ovl_lower_positive(old)) {
if (!ovl_dentry_is_whiteout(new)) {
/* Whiteout source */
flags |= RENAME_WHITEOUT;
} else {
/* Switch whiteouts */
flags |= RENAME_EXCHANGE;
}
} else if (is_dir && ovl_dentry_is_whiteout(new)) {
flags |= RENAME_EXCHANGE;
cleanup_whiteout = true;
}
}
old_upperdir = ovl_dentry_upper(old->d_parent);
new_upperdir = ovl_dentry_upper(new->d_parent);
@ -1094,6 +1080,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
ovl_drop_write(old);
out:
dput(opaquedir);
ovl_cache_free(&list);
return err;
}

3
fs/overlayfs/namei.c
View File

@ -774,6 +774,7 @@ bool ovl_lower_positive(struct dentry *dentry)
struct ovl_entry *oe = dentry->d_fsdata;
struct ovl_entry *poe = dentry->d_parent->d_fsdata;
const struct qstr *name = &dentry->d_name;
const struct cred *old_cred;
unsigned int i;
bool positive = false;
bool done = false;
@ -789,6 +790,7 @@ bool ovl_lower_positive(struct dentry *dentry)
if (!ovl_dentry_upper(dentry))
return true;
old_cred = ovl_override_creds(dentry->d_sb);
/* Positive upper -> have to look up lower to see whether it exists */
for (i = 0; !done && !positive && i < poe->numlower; i++) {
struct dentry *this;
@ -818,6 +820,7 @@ bool ovl_lower_positive(struct dentry *dentry)
dput(this);
}
}
revert_creds(old_cred);
return positive;
}

3
fs/overlayfs/readdir.c
View File

@ -862,8 +862,11 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
int err;
struct ovl_cache_entry *p, *n;
struct rb_root root = RB_ROOT;
const struct cred *old_cred;
old_cred = ovl_override_creds(dentry->d_sb);
err = ovl_dir_read_merged(dentry, list, &root);
revert_creds(old_cred);
if (err)
return err;