[GIT PULL] vfs mount

Christian Brauner
2025-01-18T13:07:06Z

Hey Linus,

/* Summary */

This contains mount update for this cycle:

- Add a mountinfo program to demonstrate statmount()/listmount()

Add a new "mountinfo" sample userland program that demonstrates how to
use statmount() and listmount() to get at the same info that
/proc/pid/mountinfo provides.

- Remove pointless nospec.h include.

- Prepend statmount.mnt_opts string with security_sb_mnt_opts()

Currently these mount options aren't accessible via statmount().

- Add new mount namespaces to mount namespace rbtree outside of the
namespace semaphore.

- Lockless mount namespace lookup

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. Currently there is no primitive for retrieving the previous
list member. To do this we need a new deletion primitive that doesn't
poison the prev pointer and a corresponding retrieval helper.

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.

- Add extended selftests for lockless mount namespace iteration.

- Add a sample program to list all mounts on the system, i.e., in all
mount namespaces.

- Improve mount namespace iteration performance

Make finding the last or first mount to start iterating the mount
namespace from an O(1) operation and add selftests for iterating the
mount table starting from the first and last mount.

- Use an xarray for the old mount id

While the ida does use the xarray internally we can use it explicitly
which allows us to increment the unique mount id under the xa lock.
This allows us to remove the atomic as we're now allocating both ids
in one go.

/* Testing */

gcc version 14.2.0 (Debian 14.2.0-6)
Debian clang version 16.0.6 (27+b1)

No build failures or warnings were observed.

/* Conflicts */

Merge conflicts with mainline
=============================

No known conflicts.

Merge conflicts with other trees
================================

This will have a merge conflict with vfs-6.14.mount pull request sent in
https://lore.kernel.org/r/20250118-vfs-pidfs-5921bfa5632a@brauner
and it can be resolved as follows:

diff --cc fs/namespace.c
index 64deda6f5b2c,371c860f49de..000000000000
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@@ -32,8 -32,6 +32,7 @@@
#include <linux/fs_context.h>
#include <linux/shmem_fs.h>
#include <linux/mnt_idmapping.h>
+#include <linux/pidfs.h>
- #include <linux/nospec.h>

#include "pnode.h"
#include "internal.h"

The following changes since commit 344bac8f0d73fe970cd9f5b2f132906317d29e8b:

fs: kill MNT_ONRB (2025-01-09 16:58:50 +0100)

are available in the Git repository at:

git@gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs tags/vfs-6.14-rc1.mount

for you to fetch changes up to f79e6eb84d4d2bff99e3ca6c1f140b2af827e904:

samples/vfs/mountinfo: Use __u64 instead of uint64_t (2025-01-10 12:08:27 +0100)

Please consider pulling these changes from the signed vfs-6.14-rc1.mount tag.

Thanks!
Christian

----------------------------------------------------------------
vfs-6.14-rc1.mount

----------------------------------------------------------------
Christian Brauner (17):
mount: remove inlude/nospec.h include
fs: add mount namespace to rbtree late
Merge patch series "fs: listmount()/statmount() fix and sample program"
fs: lockless mntns rbtree lookup
rculist: add list_bidir_{del,prev}_rcu()
fs: lockless mntns lookup for nsfs
fs: simplify rwlock to spinlock
seltests: move nsfs into filesystems subfolder
selftests: add tests for mntns iteration
selftests: remove unneeded include
samples: add test-list-all-mounts
Merge patch series "fs: lockless mntns lookup"
fs: cache first and last mount
selftests: add listmount() iteration tests
Merge patch series "fs: tweak mntns iteration"
fs: use xarray for old mount id
fs: remove useless lockdep assertion

Geert Uytterhoeven (1):
samples/vfs/mountinfo: Use __u64 instead of uint64_t

Jeff Layton (2):
samples: add a mountinfo program to demonstrate statmount()/listmount()
fs: prepend statmount.mnt_opts string with security_sb_mnt_opts()

fs/mount.h | 31 ++-
fs/namespace.c | 200 +++++++++------
fs/nsfs.c | 5 +-
include/linux/rculist.h | 44 ++++
samples/vfs/.gitignore | 2 +
samples/vfs/Makefile | 2 +-
samples/vfs/mountinfo.c | 273 +++++++++++++++++++++
samples/vfs/test-list-all-mounts.c | 235 ++++++++++++++++++
.../selftests/{ => filesystems}/nsfs/.gitignore | 1 +
.../selftests/{ => filesystems}/nsfs/Makefile | 4 +-
.../selftests/{ => filesystems}/nsfs/config | 0
.../selftests/filesystems/nsfs/iterate_mntns.c | 149 +++++++++++
.../selftests/{ => filesystems}/nsfs/owner.c | 0
.../selftests/{ => filesystems}/nsfs/pidns.c | 0
.../selftests/filesystems/statmount/Makefile | 2 +-
.../filesystems/statmount/listmount_test.c | 66 +++++
tools/testing/selftests/pidfd/pidfd.h | 1 -
17 files changed, 918 insertions(+), 97 deletions(-)
create mode 100644 samples/vfs/mountinfo.c
create mode 100644 samples/vfs/test-list-all-mounts.c
rename tools/testing/selftests/{ => filesystems}/nsfs/.gitignore (78%)
rename tools/testing/selftests/{ => filesystems}/nsfs/Makefile (50%)
rename tools/testing/selftests/{ => filesystems}/nsfs/config (100%)
create mode 100644 tools/testing/selftests/filesystems/nsfs/iterate_mntns.c
rename tools/testing/selftests/{ => filesystems}/nsfs/owner.c (100%)
rename tools/testing/selftests/{ => filesystems}/nsfs/pidns.c (100%)
create mode 100644 tools/testing/selftests/filesystems/statmount/listmount_test.c