[PATCH v5 08/14] VFS: add start_creating_killable() and start_removing_killable()

NeilBrown
2025-11-06T00:55:46Z

From: NeilBrown <neil@brown.name>

These are similar to start_creating() and start_removing(), but allow a
fatal signal to abort waiting for the lock.

They are used in btrfs for subvol creation and removal.

btrfs_may_create() no longer needs IS_DEADDIR() and
start_creating_killable() includes that check.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: NeilBrown <neil@brown.name>
---
fs/btrfs/ioctl.c | 41 +++++++---------------
fs/namei.c | 80 +++++++++++++++++++++++++++++++++++++++++--
include/linux/namei.h | 6 ++++
3 files changed, 95 insertions(+), 32 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 8cb7d5a462ef..d0c3bb0423bb 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -904,14 +904,9 @@ static noinline int btrfs_mksubvol(struct dentry *parent,
struct fscrypt_str name_str = FSTR_INIT((char *)qname->name, qname->len);
int ret;

- ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT);
- if (ret == -EINTR)
- return ret;
-
- dentry = lookup_one(idmap, qname, parent);
- ret = PTR_ERR(dentry);
+ dentry = start_creating_killable(idmap, parent, qname);
if (IS_ERR(dentry))
- goto out_unlock;
+ return PTR_ERR(dentry);

ret = btrfs_may_create(idmap, dir, dentry);
if (ret)
@@ -940,9 +935,7 @@ static noinline int btrfs_mksubvol(struct dentry *parent,
out_up_read:
up_read(&fs_info->subvol_sem);
out_dput:
- dput(dentry);
-out_unlock:
- btrfs_inode_unlock(BTRFS_I(dir), 0);
+ end_creating(dentry, parent);
return ret;
}

@@ -2417,18 +2410,10 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
goto free_subvol_name;
}

- ret = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT);
- if (ret == -EINTR)
- goto free_subvol_name;
- dentry = lookup_one(idmap, &QSTR(subvol_name), parent);
+ dentry = start_removing_killable(idmap, parent, &QSTR(subvol_name));
if (IS_ERR(dentry)) {
ret = PTR_ERR(dentry);
- goto out_unlock_dir;
- }
-
- if (d_really_is_negative(dentry)) {
- ret = -ENOENT;
- goto out_dput;
+ goto out_end_removing;
}

inode = d_inode(dentry);
@@ -2449,7 +2434,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
*/
ret = -EPERM;
if (!btrfs_test_opt(fs_info, USER_SUBVOL_RM_ALLOWED))
- goto out_dput;
+ goto out_end_removing;

/*
* Do not allow deletion if the parent dir is the same
@@ -2460,21 +2445,21 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
*/
ret = -EINVAL;
if (root == dest)
- goto out_dput;
+ goto out_end_removing;

ret = inode_permission(idmap, inode, MAY_WRITE | MAY_EXEC);
if (ret)
- goto out_dput;
+ goto out_end_removing;
}

/* check if subvolume may be deleted by a user */
ret = btrfs_may_delete(idmap, dir, dentry, 1);
if (ret)
- goto out_dput;
+ goto out_end_removing;

if (btrfs_ino(BTRFS_I(inode)) != BTRFS_FIRST_FREE_OBJECTID) {
ret = -EINVAL;
- goto out_dput;
+ goto out_end_removing;
}

btrfs_inode_lock(BTRFS_I(inode), 0);
@@ -2483,10 +2468,8 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
if (!ret)
d_delete_notify(dir, dentry);

-out_dput:
- dput(dentry);
-out_unlock_dir:
- btrfs_inode_unlock(BTRFS_I(dir), 0);
+out_end_removing:
+ end_removing(dentry);
free_subvol_name:
kfree(subvol_name_ptr);
free_parent:
diff --git a/fs/namei.c b/fs/namei.c
index 729b42fb143b..e70d056b9543 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2778,19 +2778,33 @@ static int filename_parentat(int dfd, struct filename *name,
* Returns: a locked dentry, or an error.
*
*/
-struct dentry *start_dirop(struct dentry *parent, struct qstr *name,
- unsigned int lookup_flags)
+static struct dentry *__start_dirop(struct dentry *parent, struct qstr *name,
+ unsigned int lookup_flags,
+ unsigned int state)
{
struct dentry *dentry;
struct inode *dir = d_inode(parent);

- inode_lock_nested(dir, I_MUTEX_PARENT);
+ if (state == TASK_KILLABLE) {
+ int ret = down_write_killable_nested(&dir->i_rwsem,
+ I_MUTEX_PARENT);
+ if (ret)
+ return ERR_PTR(ret);
+ } else {
+ inode_lock_nested(dir, I_MUTEX_PARENT);
+ }
dentry = lookup_one_qstr_excl(name, parent, lookup_flags);
if (IS_ERR(dentry))
inode_unlock(dir);
return dentry;
}

+struct dentry *start_dirop(struct dentry *parent, struct qstr *name,
+ unsigned int lookup_flags)
+{
+ return __start_dirop(parent, name, lookup_flags, TASK_NORMAL);
+}
+
/**
* end_dirop - signal completion of a dirop
* @de: the dentry which was returned by start_dirop or similar.
@@ -3275,6 +3289,66 @@ struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,
}
EXPORT_SYMBOL(start_removing);

+/**
+ * start_creating_killable - prepare to create a given name with permission checking
+ * @idmap: idmap of the mount
+ * @parent: directory in which to prepare to create the name
+ * @name: the name to be created
+ *
+ * Locks are taken and a lookup in performed prior to creating
+ * an object in a directory. Permission checking (MAY_EXEC) is performed
+ * against @idmap.
+ *
+ * If the name already exists, a positive dentry is returned.
+ *
+ * If a signal is received or was already pending, the function aborts
+ * with -EINTR;
+ *
+ * Returns: a negative or positive dentry, or an error.
+ */
+struct dentry *start_creating_killable(struct mnt_idmap *idmap,
+ struct dentry *parent,
+ struct qstr *name)
+{
+ int err = lookup_one_common(idmap, name, parent);
+
+ if (err)
+ return ERR_PTR(err);
+ return __start_dirop(parent, name, LOOKUP_CREATE, TASK_KILLABLE);
+}
+EXPORT_SYMBOL(start_creating_killable);
+
+/**
+ * start_removing_killable - prepare to remove a given name with permission checking
+ * @idmap: idmap of the mount
+ * @parent: directory in which to find the name
+ * @name: the name to be removed
+ *
+ * Locks are taken and a lookup in performed prior to removing
+ * an object from a directory. Permission checking (MAY_EXEC) is performed
+ * against @idmap.
+ *
+ * If the name doesn't exist, an error is returned.
+ *
+ * end_removing() should be called when removal is complete, or aborted.
+ *
+ * If a signal is received or was already pending, the function aborts
+ * with -EINTR;
+ *
+ * Returns: a positive dentry, or an error.
+ */
+struct dentry *start_removing_killable(struct mnt_idmap *idmap,
+ struct dentry *parent,
+ struct qstr *name)
+{
+ int err = lookup_one_common(idmap, name, parent);
+
+ if (err)
+ return ERR_PTR(err);
+ return __start_dirop(parent, name, 0, TASK_KILLABLE);
+}
+EXPORT_SYMBOL(start_removing_killable);
+
/**
* start_creating_noperm - prepare to create a given name without permission checking
* @parent: directory in which to prepare to create the name
diff --git a/include/linux/namei.h b/include/linux/namei.h
index d089e4e8fdd0..196c66156a8a 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -93,6 +93,12 @@ struct dentry *start_creating(struct mnt_idmap *idmap, struct dentry *parent,
struct qstr *name);
struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,
struct qstr *name);
+struct dentry *start_creating_killable(struct mnt_idmap *idmap,
+ struct dentry *parent,
+ struct qstr *name);
+struct dentry *start_removing_killable(struct mnt_idmap *idmap,
+ struct dentry *parent,
+ struct qstr *name);
struct dentry *start_creating_noperm(struct dentry *parent, struct qstr *name);
struct dentry *start_removing_noperm(struct dentry *parent, struct qstr *name);
struct dentry *start_removing_dentry(struct dentry *parent,
--
2.50.0.107.gf914562f5916.dirty