Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

1 files changed, 31 insertions, 0 deletions

diff --git a/Documentation/admin-guide/sysctl/xen.rst b/Documentation/admin-guide/sysctl/xen.rst
new file mode 100644
index 000000000..6c5edc3e5
--- /dev/null
+++ b/Documentation/admin-guide/sysctl/xen.rst
@@ -0,0 +1,31 @@
+===============
+/proc/sys/xen/
+===============
+
+Copyright (c) 2026, Shubham Chakraborty <chakrabortyshubham66@gmail.com>
+
+For general info and legal blurb, please look in
+Documentation/admin-guide/sysctl/index.rst.
+
+------------------------------------------------------------------------------
+
+These files show up in ``/proc/sys/xen/``, depending on the
+kernel configuration:
+
+.. contents:: :local:
+
+balloon/hotplug_unpopulated
+===========================
+
+This flag controls whether unpopulated memory ranges are automatically
+hotplugged as system RAM.
+
+- ``0``: Unpopulated ranges are not hotplugged (default).
+- ``1``: Unpopulated ranges are automatically hotplugged.
+
+When enabled, the Xen balloon driver will add memory regions that are
+marked as unpopulated in the Xen memory map to the system as usable RAM.
+This allows for dynamic memory expansion in Xen guest domains.
+
+This option is only available when the kernel is built with
+``CONFIG_XEN_BALLOON_MEMORY_HOTPLUG`` enabled.