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pivot_root(): reorder tree surgeries, collapse unhash_mnt() and put_mountpoint()

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attach new_mnt *before* detaching root_mnt; that way we don't need to keep hold
on the mountpoint and one more pair of unhash_mnt()/put_mountpoint() gets
folded together into umount_mnt().

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2025-04-25 16:53:01 -04:00
parent ec3265a245
commit e30da2a20e
1 changed files with 5 additions and 6 deletions
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11
fs/namespace.c
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@ -4685,7 +4685,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
{
struct path new, old, root;
struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
struct mountpoint *old_mp, *root_mp;
struct mountpoint *old_mp;
int error;
if (!may_mount())
@ -4748,20 +4748,19 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
goto out4;
lock_mount_hash();
umount_mnt(new_mnt);
root_mp = unhash_mnt(root_mnt); /* we'll need its mountpoint */
if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
new_mnt->mnt.mnt_flags |= MNT_LOCKED;
root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
}
/* mount new_root on / */
attach_mnt(new_mnt, root_parent, root_mnt->mnt_mp);
umount_mnt(root_mnt);
mnt_add_count(root_parent, -1);
/* mount old root on put_old */
attach_mnt(root_mnt, old_mnt, old_mp);
/* mount new_root on / */
attach_mnt(new_mnt, root_parent, root_mp);
mnt_add_count(root_parent, -1);
touch_mnt_namespace(current->nsproxy->mnt_ns);
/* A moved mount should not expire automatically */
list_del_init(&new_mnt->mnt_expire);
put_mountpoint(root_mp);
unlock_mount_hash();
mnt_notify_add(root_mnt);
mnt_notify_add(new_mnt);