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take ->mnt_expire handling under mount_lock [read_seqlock_excl]

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Doesn't take much massage, and we no longer need to make sure that
by the time of final mntput() the victim has been removed from the
list.  Makes life safer for ->d_automount() instances...

Rules:
	* all ->mnt_expire accesses are under mount_lock.
	* insertion into the list is done by mnt_set_expiry(), and
caller (->d_automount() instance) must hold a reference to mount
in question.  It shouldn't be done more than once for a mount.
	* if a mount on an expiry list is not yet mounted, it will
be ignored by anything that walks that list.
	* if the final mntput() finds its victim still on an expiry
list (in which case it must've never been mounted - umount_tree()
would've taken it out), it will remove the victim from the list.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2025-05-01 20:40:57 -04:00
parent a8c764e1a5
commit ec3265a245
1 changed files with 11 additions and 17 deletions
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28
fs/namespace.c
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@ -1353,13 +1353,6 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
list_add(&mnt->mnt_slave, &old->mnt_slave);
mnt->mnt_master = old->mnt_master;
}
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
if (flag & CL_EXPIRE) {
if (!list_empty(&old->mnt_expire))
list_add(&mnt->mnt_expire, &old->mnt_expire);
}
return mnt;
out_free:
@ -1452,6 +1445,8 @@ static void mntput_no_expire(struct mount *mnt)
rcu_read_unlock();
list_del(&mnt->mnt_instance);
if (unlikely(!list_empty(&mnt->mnt_expire)))
list_del(&mnt->mnt_expire);
if (unlikely(!list_empty(&mnt->mnt_mounts))) {
struct mount *p, *tmp;
@ -2273,6 +2268,13 @@ struct mount *copy_tree(struct mount *src_root, struct dentry *dentry,
lock_mount_hash();
if (src_mnt->mnt.mnt_flags & MNT_LOCKED)
dst_mnt->mnt.mnt_flags |= MNT_LOCKED;
if (unlikely(flag & CL_EXPIRE)) {
/* stick the duplicate mount on the same expiry
* list as the original if that was on one */
if (!list_empty(&src_mnt->mnt_expire))
list_add(&dst_mnt->mnt_expire,
&src_mnt->mnt_expire);
}
list_add_tail(&dst_mnt->mnt_list, &res->mnt_list);
attach_mnt(dst_mnt, dst_parent, src_parent->mnt_mp);
unlock_mount_hash();
@ -3891,12 +3893,6 @@ int finish_automount(struct vfsmount *m, const struct path *path)
namespace_unlock();
inode_unlock(dentry->d_inode);
discard:
/* remove m from any expiration list it may be on */
if (!list_empty(&mnt->mnt_expire)) {
namespace_lock();
list_del_init(&mnt->mnt_expire);
namespace_unlock();
}
mntput(m);
return err;
}
@ -3908,11 +3904,9 @@ int finish_automount(struct vfsmount *m, const struct path *path)
*/
void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
{
namespace_lock();
read_seqlock_excl(&mount_lock);
list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
namespace_unlock();
read_sequnlock_excl(&mount_lock);
}
EXPORT_SYMBOL(mnt_set_expiry);