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Christian Brauner <brauner@kernel.org> says: Currently we take the read lock when looking for a mount namespace to list mounts in. We can make this lockless. The simple search case can just use a sequence counter to detect concurrent changes to the rbtree. For walking the list of mount namespaces sequentially via nsfs we keep a separate rcu list as rb_prev() and rb_next() aren't usable safely with rcu. Since creating mount namespaces is a relatively rare event compared with querying mounts in a foreign mount namespace this is worth it. Once libmount and systemd pick up this mechanism to list mounts in foreign mount namespaces this will be used very frequently. * patches from https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-0-6e3cdaf9b280@kernel.org: samples: add test-list-all-mounts selftests: remove unneeded include selftests: add tests for mntns iteration seltests: move nsfs into filesystems subfolder fs: simplify rwlock to spinlock fs: lockless mntns lookup for nsfs rculist: add list_bidir_{del,prev}_rcu() fs: lockless mntns rbtree lookup fs: add mount namespace to rbtree late mount: remove inlude/nospec.h include Link: https://lore.kernel.org/r/20241213-work-mount-rbtree-lockless-v3-0-6e3cdaf9b280@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.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.