Pull RCU updates from Frederic Weisbecker:
 "SRCU:

   - Properly handle SRCU readers within IRQ disabled sections in tiny
     SRCU

   - Preparation to reimplement RCU Tasks Trace on top of SRCU fast:

      - Introduce API to expedite a grace period and test it through
        rcutorture

      - Split srcu-fast in two flavours: SRCU-fast and SRCU-fast-updown.

        Both are still targeted toward faster readers (without full
        barriers on LOCK and UNLOCK) at the expense of heavier write
        side (using full RCU grace period ordering instead of simply
        full ordering) as compared to "traditional" non-fast SRCU. But
        those srcu-fast flavours are going to be optimized in two
        different ways:

          - SRCU-fast will become the reimplementation basis for
            RCU-TASK-TRACE for consolidation. Since RCU-TASK-TRACE must
            be NMI safe, SRCU-fast must be as well.

          - SRCU-fast-updown will be needed for uretprobes code in order
            to get rid of the read-side memory barriers while still
            allowing entering the reader at task level while exiting it
            in a timer handler. It is considered semaphore-like in that
            it can have different owners between LOCK and UNLOCK.
            However it is not NMI-safe.

        The actual optimizations are work in progress for the next
        cycle. Only the new interfaces are added for now, along with
        related torture and scalability test code.

   - Create/document/debug/torture new proper initializers for RCU fast:
     DEFINE_SRCU_FAST() and init_srcu_struct_fast()

     This allows for using right away the proper ordering on the write
     side (either full ordering or full RCU grace period ordering)
     without waiting for the read side to tell which to use.

     This also optimizes the read side altogether with moving flavour
     debug checks under debug config and with removing a costly RmW
     operation on their first call.

   - Make some diagnostic functions tracing safe

  Refscale:

   - Add performance testing for common context synchronizations
     (Preemption, IRQ, Softirq) and per-cpu increments. Those are
     relevant comparisons against SRCU-fast read side APIs, especially
     as they are planned to synchronize further tracing fast-path code

  Miscellanous:

   - In order to prepare the layout for nohz_full work deferral to user
     exit, the context tracking state must shrink the counter of
     transitions to/from RCU not watching. The only possible hazard is
     to trigger wrap-around more easily, delaying a bit grace periods
     when that happens. This should be a rare event though. Yet add
     debugging and torture code to test that assumption

   - Fix memory leak on locktorture module

   - Annotate accesses in rculist_nulls.h to prevent from KCSAN
     warnings. On recent discussions, we also concluded that all those
     WRITE_ONCE() and READ_ONCE() on list APIs deserve appropriate
     comments. Something to be expected for the next cycle

   - Provide a script to apply several configs to several commits with
     torture

   - Allow torture to reuse a build directory in order to save needless
     rebuild time

   - Various cleanups"

* tag 'rcu.release.v6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (29 commits)
  refscale: Add SRCU-fast-updown readers
  refscale: Exercise DEFINE_STATIC_SRCU_FAST() and init_srcu_struct_fast()
  rcutorture: Make srcu{,d}_torture_init() announce the SRCU type
  srcu: Create an SRCU-fast-updown API
  refscale: Do not disable interrupts for tests involving local_bh_enable()
  refscale: Add non-atomic per-CPU increment readers
  refscale: Add this_cpu_inc() readers
  refscale: Add preempt_disable() readers
  refscale: Add local_bh_disable() readers
  refscale: Add local_irq_disable() and local_irq_save() readers
  torture: Permit negative kvm.sh --kconfig numberic arguments
  srcu: Add SRCU_READ_FLAVOR_FAST_UPDOWN CPP macro
  rcu: Mark diagnostic functions as notrace
  rcutorture: Make TREE04 use CONFIG_RCU_DYNTICKS_TORTURE
  rcutorture: Remove redundant rcutorture_one_extend() from rcu_torture_one_read()
  rcutorture: Permit kvm-again.sh to re-use the build directory
  torture: Add kvm-series.sh to test commit/scenario combination
  rcu: use WRITE_ONCE() for ->next and ->pprev of hlist_nulls
  locktorture: Fix memory leak in param_set_cpumask()
  doc: Update for SRCU-fast definitions and initialization
  ...

set_tsk_need_resched(current) requires set_preempt_need_resched(current) to
work correctly outside of the scheduler.

Provide set_need_resched_current() which wraps this correctly and replace
all the open coded instances.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251116174750.665769842@linutronix.de

The rcu_lockdep_current_cpu_online(), rcu_read_lock_sched_held(),
rcu_read_lock_held(), rcu_read_lock_bh_held(), rcu_read_lock_any_held()
are used by tracing-related code paths, so putting traces on them is
unlikely to make anyone happy.  This commit therefore marks them all
"notrace".

Reported-by: Leon Hwang <leon.hwang@linux.dev>
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Pull hyperv updates from Wei Liu:

 - Unify guest entry code for KVM and MSHV (Sean Christopherson)

 - Switch Hyper-V MSI domain to use msi_create_parent_irq_domain()
   (Nam Cao)

 - Add CONFIG_HYPERV_VMBUS and limit the semantics of CONFIG_HYPERV
   (Mukesh Rathor)

 - Add kexec/kdump support on Azure CVMs (Vitaly Kuznetsov)

 - Deprecate hyperv_fb in favor of Hyper-V DRM driver (Prasanna
   Kumar T S M)

 - Miscellaneous enhancements, fixes and cleanups (Abhishek Tiwari,
   Alok Tiwari, Nuno Das Neves, Wei Liu, Roman Kisel, Michael Kelley)

* tag 'hyperv-next-signed-20251006' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
  hyperv: Remove the spurious null directive line
  MAINTAINERS: Mark hyperv_fb driver Obsolete
  fbdev/hyperv_fb: deprecate this in favor of Hyper-V DRM driver
  Drivers: hv: Make CONFIG_HYPERV bool
  Drivers: hv: Add CONFIG_HYPERV_VMBUS option
  Drivers: hv: vmbus: Fix typos in vmbus_drv.c
  Drivers: hv: vmbus: Fix sysfs output format for ring buffer index
  Drivers: hv: vmbus: Clean up sscanf format specifier in target_cpu_store()
  x86/hyperv: Switch to msi_create_parent_irq_domain()
  mshv: Use common "entry virt" APIs to do work in root before running guest
  entry: Rename "kvm" entry code assets to "virt" to genericize APIs
  entry/kvm: KVM: Move KVM details related to signal/-EINTR into KVM proper
  mshv: Handle NEED_RESCHED_LAZY before transferring to guest
  x86/hyperv: Add kexec/kdump support on Azure CVMs
  Drivers: hv: Simplify data structures for VMBus channel close message
  Drivers: hv: util: Cosmetic changes for hv_utils_transport.c
  mshv: Add support for a new parent partition configuration
  clocksource: hyper-v: Skip unnecessary checks for the root partition
  hyperv: Add missing field to hv_output_map_device_interrupt

Rename the "kvm" entry code files and Kconfigs to use generic "virt"
nomenclature so that the code can be reused by other hypervisors (or
rather, their root/dom0 partition drivers), without incorrectly suggesting
the code somehow relies on and/or involves KVM.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistentcy cannot be addressed without refactoring the API.

alloc_workqueue() treats all queues as per-CPU by default, while unbound
workqueues must opt-in via WQ_UNBOUND.

This default is suboptimal: most workloads benefit from unbound queues,
allowing the scheduler to place worker threads where they’re needed and
reducing noise when CPUs are isolated.

This change add the WQ_UNBOUND flag to sync_wq, to make explicit this
workqueue can be unbound and that it does not benefit from per-cpu work.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
must now use WQ_PERCPU.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently if a user enqueue a work item using schedule_delayed_work() the
used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
schedule_work() that is using system_wq and queue_work(), that makes use
again of WORK_CPU_UNBOUND.
This lack of consistentcy cannot be addressed without refactoring the API.

alloc_workqueue() treats all queues as per-CPU by default, while unbound
workqueues must opt-in via WQ_UNBOUND.

This default is suboptimal: most workloads benefit from unbound queues,
allowing the scheduler to place worker threads where they’re needed and
reducing noise when CPUs are isolated.

This patch adds a new WQ_PERCPU flag to explicitly request the use of
the per-CPU behavior. Both flags coexist for one release cycle to allow
callers to transition their calls.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
must now use WQ_PERCPU.

All existing users have been updated accordingly.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds to the rcu_barrier() kerneldoc header stating that this
function hurries lazy callbacks and that it does not normally result in
additional RCU grace periods.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

RCU re-initializes the deferred QS irq work everytime before attempting
to queue it. However there are situations where the irq work is
attempted to be queued even though it is already queued. In that case
re-initializing messes-up with the irq work queue that is about to be
handled.

The chances for that to happen are higher when the architecture doesn't
support self-IPIs and irq work are then all lazy, such as with the
following sequence:

1) rcu_read_unlock() is called when IRQs are disabled and there is a
   grace period involving blocked tasks on the node. The irq work
   is then initialized and queued.

2) The related tasks are unblocked and the CPU quiescent state
   is reported. rdp->defer_qs_iw_pending is reset to DEFER_QS_IDLE,
   allowing the irq work to be requeued in the future (note the previous
   one hasn't fired yet).

3) A new grace period starts and the node has blocked tasks.

4) rcu_read_unlock() is called when IRQs are disabled again. The irq work
   is re-initialized (but it's queued! and its node is cleared) and
   requeued. Which means it's requeued to itself.

5) The irq work finally fires with the tick. But since it was requeued
   to itself, it loops and hangs.

Fix this with initializing the irq work only once before the CPU boots.

Fixes: b41642c87716 ("rcu: Fix rcu_read_unlock() deadloop due to IRQ work")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202508071303.c1134cce-lkp@intel.com
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>