linux-stable.git/kernel/cpu.c, branch v7.1.5

cpu: hotplug: Bound hotplug states sysfs output

2026-07-24T14:21:14+00:00

commit 86f436567f2516a0083b210bedc933544826a2c3 upstream.

states_show() adds CPU hotplug state names into a single sysfs buffer
using sprintf(). With enough registered states, this can write past the
end of the PAGE_SIZE buffer.

Use sysfs_emit_at() so output is bounded.

Fixes: 98f8cdce1db5 ("cpu/hotplug: Add sysfs state interface")
Signed-off-by: Bradley Morgan 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260619163719.12103-2-include@grrlz.net
Signed-off-by: Greg Kroah-Hartman

cpu: hotplug: Preserve per instance callback errors

2026-07-24T14:21:14+00:00

commit 673db10729fb121ea1b16fe57791a0cb9eac1eb5 upstream.

cpuhp_invoke_callback() unwinds earlier callbacks for the same
hotplug state when one instance fails. The rollback path currently
reuses ret, so a successful rollback can hide the original error and
make the failed transition look successful.

Keep the rollback result separate from the original error.

Fixes: 724a86881d03 ("smp/hotplug: Callback vs state-machine consistency")
Signed-off-by: Bradley Morgan 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260619163719.12103-1-include@grrlz.net
Signed-off-by: Greg Kroah-Hartman

Merge tag 'spdx-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx

2026-02-17T17:46:03+00:00

Pull SPDX updates from Greg KH:
 "Here are two small changes that add some missing SPDX license lines to
  some core kernel files. These are:

   - adding SPDX license lines to kdb files

   - adding SPDX license lines to the remaining kernel/ files

  Both of these have been in linux-next for a while with no reported
  issues"

* tag 'spdx-7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx:
  kernel: debug: Add SPDX license ids to kdb files
  kernel: add SPDX-License-Identifier lines

cpu: Provide lockdep check for CPU hotplug lock write-held

2026-02-03T14:23:33+00:00

cpuset modifies partitions, including isolated, while holding the cpu
hotplug lock read-held.

This means that write-holding the CPU hotplug lock is safe to
synchronize against housekeeping cpumask changes.

Provide a lockdep check to validate that.

Signed-off-by: Frederic Weisbecker 
Cc: Marco Crivellari 
Cc: Michal Hocko 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Cc: Thomas Gleixner 
Cc: Waiman Long 
Cc: linux-kernel@vger.kernel.org

cpu: Revert "cpu/hotplug: Prevent self deadlock on CPU hot-unplug"

2026-01-22T17:32:41+00:00

1) The commit:

	2b8272ff4a70 ("cpu/hotplug: Prevent self deadlock on CPU hot-unplug")

was added to fix an issue where the hotplug control task (BP) was
throttled between CPUHP_AP_IDLE_DEAD and CPUHP_HRTIMERS_PREPARE waiting
in the hrtimer blindspot for the bandwidth callback queued in the dead
CPU.

2) Later on, the commit:

	38685e2a0476 ("cpu/hotplug: Don't offline the last non-isolated CPU")

plugged on the target selection for the workqueue offloaded CPU down
process to prevent from destroying the last CPU domain.

3) Finally:

	5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier")

removed entirely the conditions for the race exposed and partially fixed
in 1). The offloading of the CPU down process to a workqueue on another
CPU then becomes unnecessary. But the last CPU belonging to scheduler
domains must still remain online.

Therefore revert the now obsolete commit
2b8272ff4a70b866106ae13c36be7ecbef5d5da2 and move the housekeeping check
under the cpu_hotplug_lock write held. Since HK_TYPE_DOMAIN will include
both isolcpus and cpuset isolated partition, the hotplug lock will
synchronize against concurrent cpuset partition updates.

Signed-off-by: Frederic Weisbecker 
Cc: Marco Crivellari 
Cc: Michal Hocko 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Cc: Thomas Gleixner 
Cc: Waiman Long

kernel: add SPDX-License-Identifier lines

2026-01-16T14:32:16+00:00

Add SPDX-License-Identifier lines to some old kernel
files.

Signed-off-by: Tim Bird 
Acked-by: Karim Yaghmour 
Signed-off-by: Greg Kroah-Hartman

cpu: Make atomic hotplug callbacks run with interrupts disabled on UP

2025-12-10T06:49:11+00:00

On SMP systems the CPU hotplug callbacks in the "starting" range are
invoked while the CPU is brought up and interrupts are still
disabled. Callbacks which are added later are invoked via the
hotplug-thread on the target CPU and interrupts are explicitly disabled.

In the UP case callbacks which are added later are invoked directly without
the thread indirection. This is in principle okay since there is just one
CPU but those callbacks are invoked with interrupt disabled code. That's
incorrect as those callbacks assume interrupt disabled context.

Disable interrupts before invoking the callbacks on UP if the state is
atomic and interrupts are expected to be disabled.  The "save" part is
required because this is also invoked early in the boot process while
interrupts are disabled and must not be enabled prematurely.

Fixes: 06ddd17521bf1 ("sched/smp: Always define is_percpu_thread() and scheduler_ipi()")
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20251127144723.ev9DuXXR@linutronix.de

cpumask: Cache num_possible_cpus()

2025-11-25T18:45:40+00:00

Reevaluating num_possible_cpus() over and over does not make sense. That
becomes a constant after init as cpu_possible_mask is marked ro_after_init.

Cache the value during initialization and provide that for consumption.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Yury Norov 
Reviewed-by: Mathieu Desnoyers 
Reviewed-by: Shrikanth Hegde 
Link: https://patch.msgid.link/20251119172549.578653738@linutronix.de

cpu: Remove obsolete comment from takedown_cpu()

2025-08-06T20:48:12+00:00

takedown_cpu() has a comment about "all preempt/rcu users must observe
!cpu_active()" which is kind of meaningless in this function. This
comment was originally introduced by commit 6acce3ef8452 ("sched: Remove
get_online_cpus() usage") when _cpu_down() was setting cpu_active_mask
and synchronize_rcu()/synchronize_sched() were added after that.

Later commit 40190a78f85f ("sched/hotplug: Convert cpu_[in]active
notifiers to state machine") added a new CPUHP_AP_ACTIVE hotplug
state to set/clear cpu_active_mask. The following commit b2454caa8977
("sched/hotplug: Move sync_rcu to be with set_cpu_active(false)")
move the synchronize_*() calls to sched_cpu_deactivate() associated
with the new hotplug state, but left the comment behind.

Remove this comment as it is no longer relevant in takedown_cpu().

Signed-off-by: Waiman Long 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/20250729191232.664931-1-longman@redhat.com

cpu: Define attack vectors

2025-07-11T15:55:16+00:00

Define 4 new attack vectors that are used for controlling CPU speculation
mitigations.  These may be individually disabled as part of the
mitigations= command line.  Attack vector controls are combined with global
options like 'auto' or 'auto,nosmt' like 'mitigations=auto,no_user_kernel'.
The global options come first in the mitigations= string.

Cross-thread mitigations can either remain enabled fully, including
potentially disabling SMT ('auto,nosmt'), remain enabled except for
disabling SMT ('auto'), or entirely disabled through the new
'no_cross_thread' attack vector option.

The default settings for these attack vectors are consistent with existing
kernel defaults, other than the automatic disabling of VM-based attack
vectors if KVM support is not present.

Signed-off-by: David Kaplan 
Signed-off-by: Borislav Petkov (AMD) 
Link: https://lore.kernel.org/20250707183316.1349127-3-david.kaplan@amd.com