Pull RCU updates from Paul McKenney:
 "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"

* tag 'rcu.2026.08.18a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux: (59 commits)
  rcu: Add closing parenthesis in comment in rcu_read_unlock_strict()
  rcutorture: Make {,s}rcu_read_delay() better handle forward-progress testing
  rcutorture: Announce declining to forward-progress test
  torture: Don't leak shuffle_tmp_mask when shuffler kthread fails to start
  rcutorture: Use this_cpu_inc() for rcu_torture_count[] and rcu_torture_batch[]
  rcutorture: Make RCU Tasks Trace track Reader Batches
  rcutorture: Test RCU Tasks Trace GP implying RCU GP
  rcutorture: Add a stall_only module parameter
  rcutorture: Add nwriters module parameter
  rcutorture: Use task_state_to_char() for task-state reporting
  rcutorture: Use cpumask_next_wrap() in rcu_torture_preempt()
  rcutorture: Test RCU readers from hardware interrupt handlers
  rcutorture: Check for immediate deboosting at reader end
  srcu: Queue sdp->work when the delay timer is successfully deleted
  rcu-tasks: Convert cond_resched_tasks_rcu_qs() to static inline
  rcu-tasks: Fix some comments for call_rcu_tasks() and call_rcu_tasks_rude()
  rcu-tasks: Rename tasks_rcu_exit_srcu_stall_timer to tasks_rcu_exit_stall_timer
  rcu: Mark interrupts-enabled accesses to rdp->cpu_no_qs.s
  rcu: Reduce stack usage in show_rcu_gp_kthreads()
  rcu: Mark accesses to ->rcu_urgent_qs and ->rcu_need_heavy_qs
  ...

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.

This comment is missing a closing parenthesis:

	 * The in_atomic_preempt_off() check ensures that we come here holding
	 * the last preempt_count (which will get dropped once we return to
	 * __rcu_read_unlock().

This commit therefore adds it at the end of the sentence.

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

The rcu_read_delay() and srcu_read_delay() functions are suppose to
avoid (or at least to minimize) read-side delays during call_rcu()-based
forward-progress testing.  Although rcu_read_delay() does account for
this by testing rcu_fwd_cb_nodelay, it only does so in some cases, and
srcu_read_delay() does not bother at all.  And rcutorture testing does
occasionally turn up the MIN_FWD_CBS_LAUNDERED failure when running
forward-progress tests on Tree SRCU flavors.

This commit therefore makes both rcu_read_delay() and srcu_read_delay()
take an immediate exit if rcu_fwd_cb_nodelay is set.

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

Currently, rcu_torture_fwd_prog_cr() announces function entry,
but silently exits if rcu_fwd_emergency_stop is set or if there is no
->call() function available.  This could cause confusion, leading people
to believe that rcu_torture_fwd_prog_cr() is on the job when it is not.
This commit therefore also announces the early exits from this function.

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

Currently __this_cpu_inc() is used to increment elements of both
the rcu_torture_count[] and rcu_torture_batch[] arrays.  However,
this can fail when the increments can happen in interrupt handlers,
as recently became possible.  This commit therefore upgrades the uses
of __this_cpu_inc() to the interrupt-safe this_cpu_inc().

KCSAN located this issue.

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

This commit adds the ->get_sp_seq and ->gp_diff fields to the
tasks_tracing_ops structure so that RCU Tasks Trace rcutorture runs will
track Reader Batch.

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

An RCU Tasks Trace grace period is supposed to imply an RCU grace period,
and this implication is relied on by BPF.  But this is not currently
tested.  This commit therefore makes tasks_tracing_torture_read_lock()
sometimes use rcu_read_lock() instead of rcu_read_lock_trace(), thus
testing the required implication.

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

This commit adds a stall_only module parameter that shuts off all
rcutorture kthreads other than the RCU CPU stall-warning test kthreads.
The purpose of this is to test production applictions' reactions to
CPU stalls, and with minimal additional overhead.  Or you can omit the
stall-warning tests as well and get a heavy no-op, your choice!

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

Believe it or not, there are people who would like to run rcutorture
without actually torturing RCU.  For example, some people would like to
induce various types of stall warnings without placing any unnecessary
additional overhead on their systems running in production.  And
rcutorture provides the stall_cpu, stall_cpu_holdoff, stall_no_softlockup,
stall_cpu_irqsoff, stall_cpu_block, and stall_cpu_repeat module parameters
in order to allow the user to force numerous types of stalls.  In addition,
rcutorture provides a great number of other module parameters to allow the
user to reduce other overhead.

But unfortunately, there is no way to turn of the rcu_torture_writer()
portion of this torture test, which on my x86 laptop consumes somewhere
between 40% and 45% of a CPU.  Although this is quite lightweight for a
torture test, it is not welcome on systems running production workloads.
This commit therefore adds an nwriters module parameter that defaults
to 1 but can be set to 0 in order to disable the rcu_torture_writer()
portion of the torture test, but that cannot be set to any other value
(that is what the fakewriters module parameter is for!).  This reduces
the overhead to well under 1% of a CPU, which is much more likely to be
compatible with production workloads.

Reported-by: Breno Leitao <leitao@debian.org>
Reported-by: Puranjay Mohan <puranjay@kernel.org>
Reported-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>