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commit344bac8f0dupstream. Move mnt->mnt_node into the union with mnt->mnt_rcu and mnt->mnt_llist instead of keeping it with mnt->mnt_list. This allows us to use RB_CLEAR_NODE(&mnt->mnt_node) in umount_tree() as well as list_empty(&mnt->mnt_node). That in turn allows us to remove MNT_ONRB. This also fixes the bug reported in [1] where seemingly MNT_ONRB wasn't set in @mnt->mnt_flags even though the mount was present in the mount rbtree of the mount namespace. The root cause is the following race. When a btrfs subvolume is mounted a temporary mount is created: btrfs_get_tree_subvol() { mnt = fc_mount() // Register the newly allocated mount with sb->mounts: lock_mount_hash(); list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts); unlock_mount_hash(); } and registered on sb->s_mounts. Later it is added to an anonymous mount namespace via mount_subvol(): -> mount_subvol() -> mount_subtree() -> alloc_mnt_ns() mnt_add_to_ns() vfs_path_lookup() put_mnt_ns() The mnt_add_to_ns() call raises MNT_ONRB in @mnt->mnt_flags. If someone concurrently does a ro remount: reconfigure_super() -> sb_prepare_remount_readonly() { list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) { } all mounts registered in sb->s_mounts are visited and first MNT_WRITE_HOLD is raised, then MNT_READONLY is raised, and finally MNT_WRITE_HOLD is removed again. The flag modification for MNT_WRITE_HOLD/MNT_READONLY and MNT_ONRB race so MNT_ONRB might be lost. Fixes:2eea9ce431("mounts: keep list of mounts in an rbtree") Cc: <stable@kernel.org> # v6.8+ Link: https://lore.kernel.org/r/20241215-vfs-6-14-mount-work-v1-1-fd55922c4af8@kernel.org Link: https://lore.kernel.org/r/ec6784ed-8722-4695-980a-4400d4e7bd1a@gmx.com [1] Signed-off-by: Christian Brauner <brauner@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.