Pull vfs mount updates from Christian Brauner:

 - Add FSMOUNT_NAMESPACE flag to fsmount() that creates a new mount
   namespace with the newly created filesystem attached to a copy of the
   real rootfs. This returns a namespace file descriptor instead of an
   O_PATH mount fd, similar to how OPEN_TREE_NAMESPACE works for
   open_tree().

   This allows creating a new filesystem and immediately placing it in a
   new mount namespace in a single operation, which is useful for
   container runtimes and other namespace-based isolation mechanisms.

   This accompanies OPEN_TREE_NAMESPACE and avoids a needless detour via
   OPEN_TREE_NAMESPACE to get the same effect. Will be especially useful
   when you mount an actual filesystem to be used as the container
   rootfs.

 - Currently, creating a new mount namespace always copies the entire
   mount tree from the caller's namespace. For containers and sandboxes
   that intend to build their mount table from scratch this is wasteful:
   they inherit a potentially large mount tree only to immediately tear
   it down.

   This series adds support for creating a mount namespace that contains
   only a clone of the root mount, with none of the child mounts. Two
   new flags are introduced:

     - CLONE_EMPTY_MNTNS (0x400000000) for clone3(), using the 64-bit flag space
     - UNSHARE_EMPTY_MNTNS (0x00100000) for unshare()

   Both flags imply CLONE_NEWNS. The resulting namespace contains a
   single nullfs root mount with an immutable empty directory. The
   intended workflow is to then mount a real filesystem (e.g., tmpfs)
   over the root and build the mount table from there.

 - Allow MOVE_MOUNT_BENEATH to target the caller's rootfs, allowing to
   switch out the rootfs without pivot_root(2).

   The traditional approach to switching the rootfs involves
   pivot_root(2) or a chroot_fs_refs()-based mechanism that atomically
   updates fs->root for all tasks sharing the same fs_struct. This has
   consequences for fork(), unshare(CLONE_FS), and setns().

   This series instead decomposes root-switching into individually
   atomic, locally-scoped steps:

	fd_tree = open_tree(-EBADF, "/newroot", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
	fchdir(fd_tree);
	move_mount(fd_tree, "", AT_FDCWD, "/", MOVE_MOUNT_BENEATH | MOVE_MOUNT_F_EMPTY_PATH);
	chroot(".");
	umount2(".", MNT_DETACH);

   Since each step only modifies the caller's own state, the
   fork/unshare/setns races are eliminated by design.

   A key step to making this possible is to remove the locked mount
   restriction. Originally MOVE_MOUNT_BENEATH doesn't support mounting
   beneath a mount that is locked. The locked mount protects the
   underlying mount from being revealed. This is a core mechanism of
   unshare(CLONE_NEWUSER | CLONE_NEWNS). The mounts in the new mount
   namespace become locked. That effectively makes the new mount table
   useless as the caller cannot ever get rid of any of the mounts no
   matter how useless they are.

   We can lift this restriction though. We simply transfer the locked
   property from the top mount to the mount beneath. This works because
   what we care about is to protect the underlying mount aka the parent.
   The mount mounted between the parent and the top mount takes over the
   job of protecting the parent mount from the top mount mount. This
   leaves us free to remove the locked property from the top mount which
   can consequently be unmounted:

	unshare(CLONE_NEWUSER | CLONE_NEWNS)

   and we inherit a clone of procfs on /proc then currently we cannot
   unmount it as:

	umount -l /proc

   will fail with EINVAL because the procfs mount is locked.

   After this series we can now do:

	mount --beneath -t tmpfs tmpfs /proc
	umount -l /proc

   after which a tmpfs mount has been placed beneath the procfs mount.
   The tmpfs mount has become locked and the procfs mount has become
   unlocked.

   This means you can safely modify an inherited mount table after
   unprivileged namespace creation.

   Afterwards we simply make it possible to move a mount beneath the
   rootfs allowing to upgrade the rootfs.

   Removing the locked restriction makes this very useful for containers
   created with unshare(CLONE_NEWUSER | CLONE_NEWNS) to reshuffle an
   inherited mount table safely and MOVE_MOUNT_BENEATH makes it possible
   to switch out the rootfs instead of using the costly pivot_root(2).

* tag 'vfs-7.1-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  selftests/namespaces: remove unused utils.h include from listns_efault_test
  selftests/fsmount_ns: add missing TARGETS and fix cap test
  selftests/empty_mntns: fix wrong CLONE_EMPTY_MNTNS hex value in comment
  selftests/empty_mntns: fix statmount_alloc() signature mismatch
  selftests/statmount: remove duplicate wait_for_pid()
  mount: always duplicate mount
  selftests/filesystems: add MOVE_MOUNT_BENEATH rootfs tests
  move_mount: allow MOVE_MOUNT_BENEATH on the rootfs
  move_mount: transfer MNT_LOCKED
  selftests/filesystems: add clone3 tests for empty mount namespaces
  selftests/filesystems: add tests for empty mount namespaces
  namespace: allow creating empty mount namespaces
  selftests: add FSMOUNT_NAMESPACE tests
  selftests/statmount: add statmount_alloc() helper
  tools: update mount.h header
  mount: add FSMOUNT_NAMESPACE
  mount: simplify __do_loopback()
  mount: start iterating from start of rbtree

Pull scheduler updates from Ingo Molnar:
 "Fair scheduling updates:
   - Skip SCHED_IDLE rq for SCHED_IDLE tasks (Christian Loehle)
   - Remove superfluous rcu_read_lock() in the wakeup path (K Prateek Nayak)
   - Simplify the entry condition for update_idle_cpu_scan() (K Prateek Nayak)
   - Simplify SIS_UTIL handling in select_idle_cpu() (K Prateek Nayak)
   - Avoid overflow in enqueue_entity() (K Prateek Nayak)
   - Update overutilized detection (Vincent Guittot)
   - Prevent negative lag increase during delayed dequeue (Vincent Guittot)
   - Clear buddies for preempt_short (Vincent Guittot)
   - Implement more complex proportional newidle balance (Peter Zijlstra)
   - Increase weight bits for avg_vruntime (Peter Zijlstra)
   - Use full weight to __calc_delta() (Peter Zijlstra)

  RT and DL scheduling updates:
   - Fix incorrect schedstats for rt and dl thread (Dengjun Su)
   - Skip group schedulable check with rt_group_sched=0 (Michal Koutný)
   - Move group schedulability check to sched_rt_global_validate()
     (Michal Koutný)
   - Add reporting of runtime left & abs deadline to sched_getattr()
     for DEADLINE tasks (Tommaso Cucinotta)

  Scheduling topology updates by K Prateek Nayak:
   - Compute sd_weight considering cpuset partitions
   - Extract "imb_numa_nr" calculation into a separate helper
   - Allocate per-CPU sched_domain_shared in s_data
   - Switch to assigning "sd->shared" from s_data
   - Remove sched_domain_shared allocation with sd_data

  Energy-aware scheduling updates:
   - Filter false overloaded_group case for EAS (Vincent Guittot)
   - PM: EM: Switch to rcu_dereference_all() in wakeup path
     (Dietmar Eggemann)

  Infrastructure updates:
   - Replace use of system_unbound_wq with system_dfl_wq (Marco Crivellari)

  Proxy scheduling updates by John Stultz:
   - Make class_schedulers avoid pushing current, and get rid of proxy_tag_curr()
   - Minimise repeated sched_proxy_exec() checking
   - Fix potentially missing balancing with Proxy Exec
   - Fix and improve task::blocked_on et al handling
   - Add assert_balance_callbacks_empty() helper
   - Add logic to zap balancing callbacks if we pick again
   - Move attach_one_task() and attach_task() helpers to sched.h
   - Handle blocked-waiter migration (and return migration)
   - Add K Prateek Nayak to scheduler reviewers for proxy execution

  Misc cleanups and fixes by John Stultz, Joseph Salisbury, Peter
  Zijlstra, K Prateek Nayak, Michal Koutný, Randy Dunlap, Shrikanth
  Hegde, Vincent Guittot, Zhan Xusheng, Xie Yuanbin and Vincent Guittot"

* tag 'sched-core-2026-04-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits)
  sched/eevdf: Clear buddies for preempt_short
  sched/rt: Cleanup global RT bandwidth functions
  sched/rt: Move group schedulability check to sched_rt_global_validate()
  sched/rt: Skip group schedulable check with rt_group_sched=0
  sched/fair: Avoid overflow in enqueue_entity()
  sched: Use u64 for bandwidth ratio calculations
  sched/fair: Prevent negative lag increase during delayed dequeue
  sched/fair: Use sched_energy_enabled()
  sched: Handle blocked-waiter migration (and return migration)
  sched: Move attach_one_task and attach_task helpers to sched.h
  sched: Add logic to zap balance callbacks if we pick again
  sched: Add assert_balance_callbacks_empty helper
  sched/locking: Add special p->blocked_on==PROXY_WAKING value for proxy return-migration
  sched: Fix modifying donor->blocked on without proper locking
  locking: Add task::blocked_lock to serialize blocked_on state
  sched: Fix potentially missing balancing with Proxy Exec
  sched: Minimise repeated sched_proxy_exec() checking
  sched: Make class_schedulers avoid pushing current, and get rid of proxy_tag_curr()
  MAINTAINERS: Add K Prateek Nayak to scheduler reviewers
  sched/core: Get this cpu once in ttwu_queue_cond()
  ...

Add support for creating a mount namespace that contains only a copy of
the root mount from the caller's mount namespace, with none of the
child mounts.  This is useful for containers and sandboxes that want to
start with a minimal mount table and populate it from scratch rather
than inheriting and then tearing down the full mount tree.

Two new flags are introduced:

- CLONE_EMPTY_MNTNS for clone3(), using the 64-bit flag space.

- UNSHARE_EMPTY_MNTNS for unshare(), reusing the
  CLONE_PARENT_SETTID bit which has no meaning for unshare.

Both flags imply CLONE_NEWNS.  For the unshare path,
UNSHARE_EMPTY_MNTNS is converted to CLONE_EMPTY_MNTNS in
unshare_nsproxy_namespaces() before it reaches copy_mnt_ns(), so the
mount namespace code only needs to handle a single flag.

In copy_mnt_ns(), when CLONE_EMPTY_MNTNS is set, clone_mnt() is used
instead of copy_tree() to clone only the root mount.  The caller's root
and working directory are both reset to the root dentry of the new
mount.

The cleanup variables are changed from vfsmount pointers with
__free(mntput) to struct path with __free(path_put) because the empty
mount namespace path needs to release both mount and dentry references
when replacing the caller's root and pwd.  In the normal (non-empty)
path only the mount component is set, and dput(NULL) is a no-op so
path_put remains correct there as well.

Link: https://patch.msgid.link/20260306-work-empty-mntns-consolidated-v1-1-6eb30529bbb0@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Add a new clone3() flag CLONE_PIDFD_AUTOKILL that ties a child's
lifetime to the pidfd returned from clone3(). When the last reference to
the struct file created by clone3() is closed the kernel sends SIGKILL
to the child. A pidfd obtained via pidfd_open() for the same process
does not keep the child alive and does not trigger autokill - only the
specific struct file from clone3() has this property.

This is useful for container runtimes, service managers, and sandboxed
subprocess execution - any scenario where the child must die if the
parent crashes or abandons the pidfd.

CLONE_PIDFD_AUTOKILL requires both CLONE_PIDFD (the whole point is tying
lifetime to the pidfd file) and CLONE_AUTOREAP (a killed child with no
one to reap it would become a zombie). CLONE_THREAD is rejected because
autokill targets a process not a thread.

The clone3 pidfd is identified by the PIDFD_AUTOKILL file flag set on
the struct file at clone3() time. The pidfs .release handler checks this
flag and sends SIGKILL via do_send_sig_info(SIGKILL, SEND_SIG_PRIV, ...)
only when it is set. Files from pidfd_open() or open_by_handle_at() are
distinct struct files that do not carry this flag. dup()/fork() share the
same struct file so they extend the child's lifetime until the last
reference drops.

CLONE_PIDFD_AUTOKILL uses a privilege model based on CLONE_NNP: without
CLONE_NNP the child could escalate privileges via setuid/setgid exec
after being spawned, so the caller must have CAP_SYS_ADMIN in its user
namespace. With CLONE_NNP the child can never gain new privileges so
unprivileged usage is allowed. This is a deliberate departure from the
pdeath_signal model which is reset during secureexec and commit_creds()
rendering it useless for container runtimes that need to deprivilege
themselves.

Link: https://patch.msgid.link/20260226-work-pidfs-autoreap-v5-3-d148b984a989@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Add a new clone3() flag CLONE_NNP that sets no_new_privs on the child
process at clone time. This is analogous to prctl(PR_SET_NO_NEW_PRIVS)
but applied at process creation rather than requiring a separate step
after the child starts running.

CLONE_NNP is rejected with CLONE_THREAD. It's conceptually a lot simpler
if the whole thread-group is forced into NNP and not have single threads
running around with NNP.

Link: https://patch.msgid.link/20260226-work-pidfs-autoreap-v5-2-d148b984a989@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Add a new clone3() flag CLONE_AUTOREAP that makes a child process
auto-reap on exit without ever becoming a zombie. This is a per-process
property in contrast to the existing auto-reap mechanism via
SA_NOCLDWAIT or SIG_IGN for SIGCHLD which applies to all children of a
given parent.

Currently the only way to automatically reap children is to set
SA_NOCLDWAIT or SIG_IGN on SIGCHLD. This is a parent-scoped property
affecting all children which makes it unsuitable for libraries or
applications that need selective auto-reaping of specific children while
still being able to wait() on others.

CLONE_AUTOREAP stores an autoreap flag in the child's signal_struct.
When the child exits do_notify_parent() checks this flag and causes
exit_notify() to transition the task directly to EXIT_DEAD. Since the
flag lives on the child it survives reparenting: if the original parent
exits and the child is reparented to a subreaper or init the child still
auto-reaps when it eventually exits.

CLONE_AUTOREAP can be combined with CLONE_PIDFD to allow the parent to
monitor the child's exit via poll() and retrieve exit status via
PIDFD_GET_INFO. Without CLONE_PIDFD it provides a fire-and-forget
pattern where the parent simply doesn't care about the child's exit
status. No exit signal is delivered so exit_signal must be zero.

CLONE_AUTOREAP is rejected in combination with CLONE_PARENT. If a
CLONE_AUTOREAP child were to clone(CLONE_PARENT) the new grandchild
would inherit exit_signal == 0 from the autoreap parent's group leader
but without signal->autoreap. This grandchild would become a zombie that
never sends a signal and is never autoreaped - confusing and arguably
broken behavior.

The flag is not inherited by the autoreap process's own children. Each
child that should be autoreaped must be explicitly created with
CLONE_AUTOREAP.

Link: https://github.com/uapi-group/kernel-features/issues/45
Link: https://patch.msgid.link/20260226-work-pidfs-autoreap-v5-1-d148b984a989@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

The SCHED_DEADLINE scheduler allows reading the statically configured
run-time, deadline, and period parameters through the sched_getattr()
system call. However, there is no immediate way to access, from user space,
the current parameters used within the scheduler: the instantaneous runtime
left in the current cycle, as well as the current absolute deadline.

The `flags' sched_getattr() parameter, so far mandated to contain zero,
now supports the SCHED_GETATTR_FLAG_DL_DYNAMIC=1 flag, to request
retrieval of the leftover runtime and absolute deadline, converted to a
CLOCK_MONOTONIC reference, instead of the statically configured parameters.

This feature is useful for adaptive SCHED_DEADLINE tasks that need to
modify their behavior depending on whether or not there is enough runtime
left in the current period, and/or what is the current absolute deadline.

Notes:
- before returning the instantaneous parameters, the runtime is updated;
- the abs deadline is returned shifted from rq_clock() to ktime_get_ns(),
  in CLOCK_MONOTONIC reference; this causes multiple invocations from the
  same period to return values that may differ for a few ns (showing some
  small drift), albeit the deadline doesn't move, in rq_clock() reference;
- the abs deadline value returned to user-space, as unsigned 64-bit value,
  can represent nearly 585 years since boot time;
- setting flags=0 provides the old behavior (retrieve static parameters).

See also the notes from discussion held at OSPM 2025 on the topic
"Making user space aware of current deadline-scheduler parameters".

Signed-off-by: Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Matteo Martelli <matteo.martelli@codethink.co.uk>
Link: https://patch.msgid.link/20250912053937.31636-2-tommaso.cucinotta@santannapisa.it

Implement a new scheduler class sched_ext (SCX), which allows scheduling
policies to be implemented as BPF programs to achieve the following:

1. Ease of experimentation and exploration: Enabling rapid iteration of new
   scheduling policies.

2. Customization: Building application-specific schedulers which implement
   policies that are not applicable to general-purpose schedulers.

3. Rapid scheduler deployments: Non-disruptive swap outs of scheduling
   policies in production environments.

sched_ext leverages BPF’s struct_ops feature to define a structure which
exports function callbacks and flags to BPF programs that wish to implement
scheduling policies. The struct_ops structure exported by sched_ext is
struct sched_ext_ops, and is conceptually similar to struct sched_class. The
role of sched_ext is to map the complex sched_class callbacks to the more
simple and ergonomic struct sched_ext_ops callbacks.

For more detailed discussion on the motivations and overview, please refer
to the cover letter.

Later patches will also add several example schedulers and documentation.

This patch implements the minimum core framework to enable implementation of
BPF schedulers. Subsequent patches will gradually add functionalities
including safety guarantee mechanisms, nohz and cgroup support.

include/linux/sched/ext.h defines struct sched_ext_ops. With the comment on
top, each operation should be self-explanatory. The followings are worth
noting:

- Both "sched_ext" and its shorthand "scx" are used. If the identifier
  already has "sched" in it, "ext" is used; otherwise, "scx".

- In sched_ext_ops, only .name is mandatory. Every operation is optional and
  if omitted a simple but functional default behavior is provided.

- A new policy constant SCHED_EXT is added and a task can select sched_ext
  by invoking sched_setscheduler(2) with the new policy constant. However,
  if the BPF scheduler is not loaded, SCHED_EXT is the same as SCHED_NORMAL
  and the task is scheduled by CFS. When the BPF scheduler is loaded, all
  tasks which have the SCHED_EXT policy are switched to sched_ext.

- To bridge the workflow imbalance between the scheduler core and
  sched_ext_ops callbacks, sched_ext uses simple FIFOs called dispatch
  queues (dsq's). By default, there is one global dsq (SCX_DSQ_GLOBAL), and
  one local per-CPU dsq (SCX_DSQ_LOCAL). SCX_DSQ_GLOBAL is provided for
  convenience and need not be used by a scheduler that doesn't require it.
  SCX_DSQ_LOCAL is the per-CPU FIFO that sched_ext pulls from when putting
  the next task on the CPU. The BPF scheduler can manage an arbitrary number
  of dsq's using scx_bpf_create_dsq() and scx_bpf_destroy_dsq().

- sched_ext guarantees system integrity no matter what the BPF scheduler
  does. To enable this, each task's ownership is tracked through
  p->scx.ops_state and all tasks are put on scx_tasks list. The disable path
  can always recover and revert all tasks back to CFS. See p->scx.ops_state
  and scx_tasks.

- A task is not tied to its rq while enqueued. This decouples CPU selection
  from queueing and allows sharing a scheduling queue across an arbitrary
  subset of CPUs. This adds some complexities as a task may need to be
  bounced between rq's right before it starts executing. See
  dispatch_to_local_dsq() and move_task_to_local_dsq().

- One complication that arises from the above weak association between task
  and rq is that synchronizing with dequeue() gets complicated as dequeue()
  may happen anytime while the task is enqueued and the dispatch path might
  need to release the rq lock to transfer the task. Solving this requires a
  bit of complexity. See the logic around p->scx.sticky_cpu and
  p->scx.ops_qseq.

- Both enable and disable paths are a bit complicated. The enable path
  switches all tasks without blocking to avoid issues which can arise from
  partially switched states (e.g. the switching task itself being starved).
  The disable path can't trust the BPF scheduler at all, so it also has to
  guarantee forward progress without blocking. See scx_ops_enable() and
  scx_ops_disable_workfn().

- When sched_ext is disabled, static_branches are used to shut down the
  entry points from hot paths.

v7: - scx_ops_bypass() was incorrectly and unnecessarily trying to grab
      scx_ops_enable_mutex which can lead to deadlocks in the disable path.
      Fixed.

    - Fixed TASK_DEAD handling bug in scx_ops_enable() path which could lead
      to use-after-free.

    - Consolidated per-cpu variable usages and other cleanups.

v6: - SCX_NR_ONLINE_OPS replaced with SCX_OPI_*_BEGIN/END so that multiple
      groups can be expressed. Later CPU hotplug operations are put into
      their own group.

    - SCX_OPS_DISABLING state is replaced with the new bypass mechanism
      which allows temporarily putting the system into simple FIFO
      scheduling mode bypassing the BPF scheduler. In addition to the shut
      down path, this will also be used to isolate the BPF scheduler across
      PM events. Enabling and disabling the bypass mode requires iterating
      all runnable tasks. rq->scx.runnable_list addition is moved from the
      later watchdog patch.

    - ops.prep_enable() is replaced with ops.init_task() and
      ops.enable/disable() are now called whenever the task enters and
      leaves sched_ext instead of when the task becomes schedulable on
      sched_ext and stops being so. A new operation - ops.exit_task() - is
      called when the task stops being schedulable on sched_ext.

    - scx_bpf_dispatch() can now be called from ops.select_cpu() too. This
      removes the need for communicating local dispatch decision made by
      ops.select_cpu() to ops.enqueue() via per-task storage.
      SCX_KF_SELECT_CPU is added to support the change.

    - SCX_TASK_ENQ_LOCAL which told the BPF scheudler that
      scx_select_cpu_dfl() wants the task to be dispatched to the local DSQ
      was removed. Instead, scx_bpf_select_cpu_dfl() now dispatches directly
      if it finds a suitable idle CPU. If such behavior is not desired,
      users can use scx_bpf_select_cpu_dfl() which returns the verdict in a
      bool out param.

    - scx_select_cpu_dfl() was mishandling WAKE_SYNC and could end up
      queueing many tasks on a local DSQ which makes tasks to execute in
      order while other CPUs stay idle which made some hackbench numbers
      really bad. Fixed.

    - The current state of sched_ext can now be monitored through files
      under /sys/sched_ext instead of /sys/kernel/debug/sched/ext. This is
      to enable monitoring on kernels which don't enable debugfs.

    - sched_ext wasn't telling BPF that ops.dispatch()'s @prev argument may
      be NULL and a BPF scheduler which derefs the pointer without checking
      could crash the kernel. Tell BPF. This is currently a bit ugly. A
      better way to annotate this is expected in the future.

    - scx_exit_info updated to carry pointers to message buffers instead of
      embedding them directly. This decouples buffer sizes from API so that
      they can be changed without breaking compatibility.

    - exit_code added to scx_exit_info. This is used to indicate different
      exit conditions on non-error exits and will be used to handle e.g. CPU
      hotplugs.

    - The patch "sched_ext: Allow BPF schedulers to switch all eligible
      tasks into sched_ext" is folded in and the interface is changed so
      that partial switching is indicated with a new ops flag
      %SCX_OPS_SWITCH_PARTIAL. This makes scx_bpf_switch_all() unnecessasry
      and in turn SCX_KF_INIT. ops.init() is now called with
      SCX_KF_SLEEPABLE.

    - Code reorganized so that only the parts necessary to integrate with
      the rest of the kernel are in the header files.

    - Changes to reflect the BPF and other kernel changes including the
      addition of bpf_sched_ext_ops.cfi_stubs.

v5: - To accommodate 32bit configs, p->scx.ops_state is now atomic_long_t
      instead of atomic64_t and scx_dsp_buf_ent.qseq which uses
      load_acquire/store_release is now unsigned long instead of u64.

    - Fix the bug where bpf_scx_btf_struct_access() was allowing write
      access to arbitrary fields.

    - Distinguish kfuncs which can be called from any sched_ext ops and from
      anywhere. e.g. scx_bpf_pick_idle_cpu() can now be called only from
      sched_ext ops.

    - Rename "type" to "kind" in scx_exit_info to make it easier to use on
      languages in which "type" is a reserved keyword.

    - Since cff9b2332ab7 ("kernel/sched: Modify initial boot task idle
      setup"), PF_IDLE is not set on idle tasks which haven't been online
      yet which made scx_task_iter_next_filtered() include those idle tasks
      in iterations leading to oopses. Update scx_task_iter_next_filtered()
      to directly test p->sched_class against idle_sched_class instead of
      using is_idle_task() which tests PF_IDLE.

    - Other updates to match upstream changes such as adding const to
      set_cpumask() param and renaming check_preempt_curr() to
      wakeup_preempt().

v4: - SCHED_CHANGE_BLOCK replaced with the previous
      sched_deq_and_put_task()/sched_enq_and_set_tsak() pair. This is
      because upstream is adaopting a different generic cleanup mechanism.
      Once that lands, the code will be adapted accordingly.

    - task_on_scx() used to test whether a task should be switched into SCX,
      which is confusing. Renamed to task_should_scx(). task_on_scx() now
      tests whether a task is currently on SCX.

    - scx_has_idle_cpus is barely used anymore and replaced with direct
      check on the idle cpumask.

    - SCX_PICK_IDLE_CORE added and scx_pick_idle_cpu() improved to prefer
      fully idle cores.

    - ops.enable() now sees up-to-date p->scx.weight value.

    - ttwu_queue path is disabled for tasks on SCX to avoid confusing BPF
      schedulers expecting ->select_cpu() call.

    - Use cpu_smt_mask() instead of topology_sibling_cpumask() like the rest
      of the scheduler.

v3: - ops.set_weight() added to allow BPF schedulers to track weight changes
      without polling p->scx.weight.

    - move_task_to_local_dsq() was losing SCX-specific enq_flags when
      enqueueing the task on the target dsq because it goes through
      activate_task() which loses the upper 32bit of the flags. Carry the
      flags through rq->scx.extra_enq_flags.

    - scx_bpf_dispatch(), scx_bpf_pick_idle_cpu(), scx_bpf_task_running()
      and scx_bpf_task_cpu() now use the new KF_RCU instead of
      KF_TRUSTED_ARGS to make it easier for BPF schedulers to call them.

    - The kfunc helper access control mechanism implemented through
      sched_ext_entity.kf_mask is improved. Now SCX_CALL_OP*() is always
      used when invoking scx_ops operations.

v2: - balance_scx_on_up() is dropped. Instead, on UP, balance_scx() is
      called from put_prev_taks_scx() and pick_next_task_scx() as necessary.
      To determine whether balance_scx() should be called from
      put_prev_task_scx(), SCX_TASK_DEQD_FOR_SLEEP flag is added. See the
      comment in put_prev_task_scx() for details.

    - sched_deq_and_put_task() / sched_enq_and_set_task() sequences replaced
      with SCHED_CHANGE_BLOCK().

    - Unused all_dsqs list removed. This was a left-over from previous
      iterations.

    - p->scx.kf_mask is added to track and enforce which kfunc helpers are
      allowed. Also, init/exit sequences are updated to make some kfuncs
      always safe to call regardless of the current BPF scheduler state.
      Combined, this should make all the kfuncs safe.

    - BPF now supports sleepable struct_ops operations. Hacky workaround
      removed and operations and kfunc helpers are tagged appropriately.

    - BPF now supports bitmask / cpumask helpers. scx_bpf_get_idle_cpumask()
      and friends are added so that BPF schedulers can use the idle masks
      with the generic helpers. This replaces the hacky kfunc helpers added
      by a separate patch in V1.

    - CONFIG_SCHED_CLASS_EXT can no longer be enabled if SCHED_CORE is
      enabled. This restriction will be removed by a later patch which adds
      core-sched support.

    - Add MAINTAINERS entries and other misc changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Co-authored-by: David Vernet <dvernet@meta.com>
Acked-by: Josh Don <joshdon@google.com>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Barret Rhoden <brho@google.com>
Cc: Andrea Righi <andrea.righi@canonical.com>

This adds support for creating a process in a different cgroup than its
parent. Callers can limit and account processes and threads right from
the moment they are spawned:
- A service manager can directly spawn new services into dedicated
  cgroups.
- A process can be directly created in a frozen cgroup and will be
  frozen as well.
- The initial accounting jitter experienced by process supervisors and
  daemons is eliminated with this.
- Threaded applications or even thread implementations can choose to
  create a specific cgroup layout where each thread is spawned
  directly into a dedicated cgroup.

This feature is limited to the unified hierarchy. Callers need to pass
a directory file descriptor for the target cgroup. The caller can
choose to pass an O_PATH file descriptor. All usual migration
restrictions apply, i.e. there can be no processes in inner nodes. In
general, creating a process directly in a target cgroup adheres to all
migration restrictions.

One of the biggest advantages of this feature is that CLONE_INTO_GROUP does
not need to grab the write side of the cgroup cgroup_threadgroup_rwsem.
This global lock makes moving tasks/threads around super expensive. With
clone3() this lock is avoided.

Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Time Namespace isolates clock values.

The kernel provides access to several clocks CLOCK_REALTIME,
CLOCK_MONOTONIC, CLOCK_BOOTTIME, etc.

CLOCK_REALTIME
      System-wide clock that measures real (i.e., wall-clock) time.

CLOCK_MONOTONIC
      Clock that cannot be set and represents monotonic time since
      some unspecified starting point.

CLOCK_BOOTTIME
      Identical to CLOCK_MONOTONIC, except it also includes any time
      that the system is suspended.

For many users, the time namespace means the ability to changes date and
time in a container (CLOCK_REALTIME). Providing per namespace notions of
CLOCK_REALTIME would be complex with a massive overhead, but has a dubious
value.

But in the context of checkpoint/restore functionality, monotonic and
boottime clocks become interesting. Both clocks are monotonic with
unspecified starting points. These clocks are widely used to measure time
slices and set timers. After restoring or migrating processes, it has to be
guaranteed that they never go backward. In an ideal case, the behavior of
these clocks should be the same as for a case when a whole system is
suspended. All this means that it is required to set CLOCK_MONOTONIC and
CLOCK_BOOTTIME clocks, which can be achieved by adding per-namespace
offsets for clocks.

A time namespace is similar to a pid namespace in the way how it is
created: unshare(CLONE_NEWTIME) system call creates a new time namespace,
but doesn't set it to the current process. Then all children of the process
will be born in the new time namespace, or a process can use the setns()
system call to join a namespace.

This scheme allows setting clock offsets for a namespace, before any
processes appear in it.

All available clone flags have been used, so CLONE_NEWTIME uses the highest
bit of CSIGNAL. It means that it can be used only with the unshare() and
the clone3() system calls.

[ tglx: Adjusted paragraph about clone3() to reality and massaged the
  	changelog a bit. ]

Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://criu.org/Time_namespace
Link: https://lists.openvz.org/pipermail/criu/2018-June/041504.html
Link: https://lore.kernel.org/r/20191112012724.250792-4-dima@arista.com