Pull NOHZ updates from Thomas Gleixner:
- Fix a long standing TOCTOU in get_cpu_sleep_time_us()
- Make the CPU offline NOHZ handling more robust by disabling NOHZ on
the outgoing CPU early instead of creating unneeded state which needs
to be undone.
- Unify idle CPU time accounting instead of having two different
accounting mechanisms. These two different mechanisms are not really
independent, but the different properties can in the worst case cause
that gloabl idle time can be observed going backwards.
- Consolidate the idle/iowait time retrieval interfaces instead of
converting back and forth between them.
- Make idle interrupt time accounting more robust. The original code
assumes that interrupt time accouting is enabled and therefore stops
elapsing idle time while an interrupt is handled in NOHZ dyntick
state. That assumption is not correct as interrupt time accounting
can be disabled at compile and runtime.
- Fix an accounting error between dyntick idle time and dyntick idle
steal time. The stolen time is not accounted and therefore idle time
becomes inaccurate. The stolen time is now accounted after the fact
as there is no way to predict the steal time upfront.
* tag 'timers-nohz-2026-06-13' of gitolite.kernel.org:pub/scm/linux/kernel/git/tip/tip:
sched/cputime: Handle dyntick-idle steal time correctly
sched/cputime: Handle idle irqtime gracefully
sched/cputime: Provide get_cpu_[idle|iowait]_time_us() off-case
tick/sched: Consolidate idle time fetching APIs
tick/sched: Account tickless idle cputime only when tick is stopped
tick/sched: Remove unused fields
tick/sched: Move dyntick-idle cputime accounting to cputime code
tick/sched: Remove nohz disabled special case in cputime fetch
tick/sched: Unify idle cputime accounting
s390/time: Prepare to stop elapsing in dynticks-idle
powerpc/time: Prepare to stop elapsing in dynticks-idle
sched/cputime: Correctly support generic vtime idle time
sched/cputime: Remove superfluous and error prone kcpustat_field() parameter
sched/idle: Handle offlining first in idle loop
tick/sched: Fix TOCTOU in nohz idle time fetch
Pull RCU updates from Uladzislau Rezki:
"Torture test updates:
- Improve kvm-series.sh script by adding examples in its header
comment
- Lazy RCU is more fully tested now by replacing call_rcu_hurry()
with call_rcu() and doing rcu_barrier() to motivate lazy callbacks
during a stutter pause
- Add more synonyms for the "--do-normal" group of torture.sh
command-line arguments
Misc changes:
- Reduce stack usage of nocb_gp_wait() to address frame size warning
when built with CONFIG_UBSAN_ALIGNMENT
- The synchronize_rcu() call can detect the flood and latches a
normal/default path temporary switching to wait_rcu_gp() path
- Document using rcu_access_pointer() to fetch the old pointer for
lockless cmpxchg() updates
- Simplify some RCU code using clamp_val()
- Fix a kerneldoc header comment typo in srcu_down_read_fast()"
* tag 'rcu.release.v7.2' of gitolite.kernel.org:pub/scm/linux/kernel/git/rcu/linux:
rcu/nocb: reduce stack usage in nocb_gp_wait()
rcu-tasks: Fix possible boot-time tests failed for the call_rcu_tasks()
rcu: Latch normal synchronize_rcu() path on flood
rcu: Document rcu_access_pointer() feeding into cmpxchg()
rcu: Simplify param_set_next_fqs_jiffies() by applying clamp_val()
rcu: Simplify rcu_do_batch() by applying clamp()
checkpatch: Undeprecate rcu_read_lock_trace() and rcu_read_unlock_trace()
srcu: Fix kerneldoc header comment typo in srcu_down_read_fast()
torture: Allow "norm" abbreviation for "normal"
torture: Improve kvm-series.sh header comment
torture: Add torture_sched_set_normal() for user-specified nice values
rcutorture: Fully test lazy RCU
The first parameter to kcpustat_field() is a pointer to the cpu kcpustat to
be fetched from. This parameter is error prone because a copy to a kcpustat
could be passed by accident instead of the original one. Also the kcpustat
structure can already be retrieved with the help of the mandatory CPU
argument.
Remove the needless parameter.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-4-frederic@kernel.org
When CONFIG_UBSAN_ALIGNMENT is enabled, the stack usage of nocb_gp_wait()
grows above typical warning limits:
In file included from kernel/rcu/tree.c:4930:
kernel/rcu/tree_nocb.h: In function 'rcu_nocb_gp_kthread':
kernel/rcu/tree_nocb.h:866:1: error: the frame size of 1968 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
Apparently, the problem is passing rcu_data from a 'void *' pointer,
which gcc assumes may be misaligned. When the function is not inlined
into rcu_nocb_gp_kthread(), that is no longer visible to gcc.
Add a 'noinline_for_stack' annotation that leads to skipping a lot of
the alignment sanitizer checks and keeps the stack usage 60% lower here.
Reviewed-by: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
The following scenarios will cause the call_rcu_tasks() boot-time
tests failed:
CPU0 CPU1
rcu_init_tasks_generic()
->rcu_tasks_initiate_self_tests()
->call_rcu_tasks_trace(&tests[1].rh, test_rcu_tasks_callback)
->call_rcu_tasks_generic()
->havekthread = smp_load_acquire(&rtp->kthread_ptr)
"The havekthread is false"
....
rcu_tasks_kthread()
->smp_store_release(&rtp->kthread_ptr, current)
->rcu_tasks_one_gp()
->rcuwait_wait_event()
->rcu_tasks_need_gpcb()
->for (cpu = 0; cpu < dequeue_limit; cpu++)
->rcu_segcblist_n_cbs(&rtpcp->cblist) == 0
->schedule()
->raw_spin_trylock_rcu_node()
->needwake = (func == wakeme_after_rcu) ||
(rcu_segcblist_n_cbs(&rtpcp->cblist) == rcu_task_lazy_lim)
"the rcu_task_lazy_lim default value is 32, and the
func pointer is test_rcu_tasks_callback, lead to needwake
is false."
->if (havekthread && !needwake && !timer_pending(&rtpcp->lazy_timer))
"the havekthread is false, will not enter here."
....
"the needwake is false lead to rtp_irq_work can not queue,
even if the rtp->kthread_ptr already exists at this point."
->if (needwake && READ_ONCE(rtp->kthread_ptr))
->irq_work_queue(&rtpcp->rtp_irq_work)
For the above scenarios, if the call_rcu_tasks() is not called again
afterward, the rcu_tasks_kthread will not have a chance to be wakeup,
the test_rcu_tasks_callback() will never be called, the boot-time tests
failed can happen, this commit therefore check havekthread variable, if
it's false and the rtpcp->cblist is empty, set needwake variable is true,
if the rtp->kthread_ptr exist, the rtpcp->rtp_irq_work can be queued to
wakeup rcu_tasks_kthread.
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Currently, rcu_normal_wake_from_gp is only enabled by default
on small systems(<= 16 CPUs) or when a user explicitly set it
enabled.
Introduce an adaptive latching mechanism:
* Track the number of in-flight synchronize_rcu() requests
using a new rcu_sr_normal_count counter;
* If the count reaches/exceeds RCU_SR_NORMAL_LATCH_THR(64),
it sets the rcu_sr_normal_latched, reverting new requests
onto the scaled wait_rcu_gp() path;
* The latch is cleared only when the pending requests are fully
drained(nr == 0);
* Enables rcu_normal_wake_from_gp by default for all systems,
relying on this dynamic throttling instead of static CPU
limits.
Testing(synthetic flood workload):
* Kernel version: 6.19.0-rc6
* Number of CPUs: 1536
* 60K concurrent synchronize_rcu() calls
Perf(cycles, system-wide):
total cycles: 932020263832
rcu_sr_normal_add_req(): 2650282811 cycles(~0.28%)
Perf report excerpt:
0.01% 0.01% sync_test/... [k] rcu_sr_normal_add_req
Measured overhead of rcu_sr_normal_add_req() remained ~0.28%
of total CPU cycles in this synthetic stress test.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Tested-by: Samir M <samir@linux.ibm.com>
Suggested-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit replaces a nested ?: sequence with clamp_val(). This does
not reduce the number of lines of code, but it does simplify the line
that it modifies.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit replaces a nested ?: sequence with clamp(). This does not
reduce the number of lines of code, but it does simplify the line that
it modifies.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Currently, rcutorture bypasses lazy RCU by using call_rcu_hurry().
This works, avoiding the dreaded rtort_pipe_count WARN(), but fails to
fully test lazy RCU. The rtort_pipe_count WARN() splats because lazy RCU
could delay the start of an RCU grace period for a full stutter period,
which defaults to only three seconds.
This commit therefore reverts the call_rcu_hurry() instances
back to call_rcu(), but, in kernels built with CONFIG_RCU_LAZY=y,
queues a workqueue handler just before the call to stutter_wait() in
rcu_torture_writer(). This workqueue handler invokes rcu_barrier(),
which motivates any lingering lazy callbacks, thus avoiding the splat.
Reported-by: Saravana Kannan <saravanak@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
While an srcu_struct structure is in the midst of switching from CPU-0
to all-CPUs state, it can attempt to invoke callbacks for CPUs that
have never been online. Worse yet, it can attempt in invoke callbacks
for CPUs that never will be online, even including imaginary CPUs not in
cpu_possible_mask. This can cause hangs on s390, which is not set up to
deal with workqueue handlers being scheduled on such CPUs. This commit
therefore causes Tree SRCU to refrain from queueing workqueue handlers
on CPUs that have not yet (and might never) come online.
Because callbacks are not invoked on CPUs that have not been
online, it is an error to invoke call_srcu(), synchronize_srcu(), or
synchronize_srcu_expedited() on a CPU that is not yet fully online.
However, it turns out to be less code to redirect the callbacks
from too-early invocations of call_srcu() than to warn about such
invocations. This commit therefore also redirects callbacks queued on
not-yet-fully-online CPUs to the boot CPU.
Reported-by: Vasily Gorbik <gor@linux.ibm.com>
Fixes: 61bbcfb505 ("srcu: Push srcu_node allocation to GP when non-preemptible")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Vasily Gorbik <gor@linux.ibm.com>
Tested-by: Samir <samir@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Pull RCU updates from Joel Fernandes:
"NOCB CPU management:
- Consolidate rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() to
reduce code duplication
- Extract nocb_bypass_needs_flush() helper to reduce duplication in
NOCB bypass path
rcutorture/torture infrastructure:
- Add NOCB01 config for RCU_LAZY torture testing
- Add NOCB02 config for NOCB poll mode testing
- Add TRIVIAL-PREEMPT config for textbook-style preemptible RCU
torture
- Test call_srcu() with preemption both disabled and enabled
- Remove kvm-check-branches.sh in favor of kvm-series.sh
- Make hangs more visible in torture.sh output
- Add informative message for tests without a recheck file
- Fix numeric test comparison in srcu_lockdep.sh
- Use torture_shutdown_init() in refscale and rcuscale instead of
open-coded shutdown functions
- Fix modulo-zero error in torture_hrtimeout_ns().
SRCU:
- Fix SRCU read flavor macro comments
- Fix s/they disables/they disable/ typo in srcu_read_unlock_fast()
RCU Tasks:
- Document that RCU Tasks Trace grace periods now imply RCU grace
periods
- Remove unnecessary smp_store_release() in cblist_init_generic()"
* tag 'rcu.2026.03.31a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux:
rcutorture: Test call_srcu() with preemption disabled and not
rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option
torture: Avoid modulo-zero error in torture_hrtimeout_ns()
rcu/nocb: Extract nocb_bypass_needs_flush() to reduce duplication
rcu/nocb: Consolidate rcu_nocb_cpu_offload/deoffload functions
rcu-tasks: Remove unnecessary smp_store_release() in cblist_init_generic()
rcutorture: Add NOCB02 config for nocb poll mode testing
rcutorture: Add NOCB01 config for RCU_LAZY torture testing
rcu-tasks: Document that RCU Tasks Trace grace periods now imply RCU grace periods
srcu: Fix s/they disables/they disable/ typo in srcu_read_unlock_fast()
srcu: Fix SRCU read flavor macro comments
rcuscale: Ditch rcu_scale_shutdown in favor of torture_shutdown_init()
refscale: Ditch ref_scale_shutdown in favor of torture_shutdown_init()
rcutorture: Fix numeric "test" comparison in srcu_lockdep.sh
torture: Print informative message for test without recheck file
torture: Make hangs more visible in torture.sh output
kvm-check-branches.sh: Remove in favor of kvm-series.sh
rcutorture: Add a textbook-style trivial preemptible RCU
This commit tests invoking call_srcu() with preemption both enabled
and disabled, via acquiring of pi lock.
[ Joel: reword commit message. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Add a Kconfig option to set the default value of the
kernel.panic_on_rcu_stall sysctl, allowing the kernel to be built
with panic-on-RCU-stall enabled by default.
This is useful for high-availability systems that require automatic
recovery (via panic_timeout) when a CPU stall is detected, without
needing userspace to configure the sysctl at boot.
This follows the pattern established by BOOTPARAM_SOFTLOCKUP_PANIC
and BOOTPARAM_HUNG_TASK_PANIC. The runtime sysctl can still override
the Kconfig default.
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
The bypass flush decision logic is duplicated in rcu_nocb_try_bypass()
and nocb_gp_wait() with similar conditions.
This commit therefore extracts the functionality into a common helper
function nocb_bypass_needs_flush() improving the code readability.
A flush_faster parameter is added to controlling the flushing thresholds
and timeouts. This design was in the original commit d1b222c6be
("rcu/nocb: Add bypass callback queueing") to avoid having the GP
kthread aggressively flush the bypass queue.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
The rcu_nocb_cpu_offload() and rcu_nocb_cpu_deoffload() functions are
nearly duplicates.
Therefore, extract the common logic into rcu_nocb_cpu_toggle_offload()
which takes an 'offload' boolean, and make both exported functions
simple wrappers.
This eliminates a bunch of duplicate code at the call sites, namely
mutex locking, CPU hotplug locking and CPU online checks.
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
The cblist_init_generic() is executed during the CPU early boot
phase due to commit:30ef09635b9e ("rcu-tasks: Initialize callback
lists at rcu_init() time"), at this time, only one boot CPU is
online and the irq is disabled. this commit therefore use routine
assignment replace of smp_store_release() and WRITE_ONCE() in the
cblist_init_generic().
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
The torture_shutdown_init() function spawns a shutdown kthread in
a manner very similar to that implemented by rcu_scale_shutdown().
This commit therefore re-implements rcu_scale_shutdown() in terms of
torture_shutdown_init().
This patch was generated by Claude given as input the patch making the
same transformation of ref_scale_shutdown().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
The torture_shutdown_init() function spawns a shutdown kthread in
a manner very similar to that implemented by ref_scale_shutdown().
This commit therefore re-implements ref_scale_shutdown in terms of
torture_shutdown_init().
The initial draft of this patch was generated by version 2.1.16 of the
Claude AI/LLM, but trained and configured for use by my employer, and
prompted to refer to Linux-kernel source code. This initial draft failed
to provide a forward reference to ref_scale_cleanup(), passed zero to
torture_shutdown_init() for an unwelcome insta-shutdown, and failed to
pass the kvm.sh --duration argument in as a refscale module parameter.
On the other hand, it did catch the need to NULL main_task on the
post-test self-shutdown code path, which I might well have forgotten
to do.
This version of the patch fixes those problems, and in fact very little
of the initial draft remains.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
This commit adds a trivial textbook implementation of preemptible RCU
to rcutorture ("torture_type=trivial-preempt"), similar in spirit to the
existing "torture_type=trivial" textbook implementation of non-preemptible
RCU. Neither trivial RCU implementation has any value for production use,
and are intended only to keep Paul honest in his introductory writings
and presentations.
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Tiny SRCU's srcu_gp_start_if_needed() directly calls schedule_work(),
which acquires the workqueue pool->lock.
This causes a lockdep splat when call_srcu() is called with a scheduler
lock held, due to:
call_srcu() [holding pi_lock]
srcu_gp_start_if_needed()
schedule_work() -> pool->lock
workqueue_init() / create_worker() [holding pool->lock]
wake_up_process() -> try_to_wake_up() -> pi_lock
Also add irq_work_sync() to cleanup_srcu_struct() to prevent a
use-after-free if a queued irq_work fires after cleanup begins.
Tested with rcutorture SRCU-T and no lockdep warnings.
[ Thanks to Boqun for similar fix in patch "rcu: Use an intermediate irq_work
to start process_srcu()" ]
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Since commit c27cea4416 ("rcu: Re-implement RCU Tasks Trace in terms
of SRCU-fast") we switched to SRCU in BPF. However as BPF instrument can
happen basically everywhere (including where a scheduler lock is held),
call_srcu() now needs to avoid acquiring scheduler lock because
otherwise it could cause deadlock [1]. Fix this by following what the
previous RCU Tasks Trace did: using an irq_work to delay the queuing of
the work to start process_srcu().
[boqun: Apply Joel's feedback]
[boqun: Apply Andrea's test feedback]
Reported-by: Andrea Righi <arighi@nvidia.com>
Closes: https://lore.kernel.org/all/abjzvz_tL_siV17s@gpd4/
Fixes: commit c27cea4416 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
Link: https://lore.kernel.org/rcu/3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com/ [1]
Suggested-by: Zqiang <qiang.zhang@linux.dev>
Tested-by: Andrea Righi <arighi@nvidia.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun@kernel.org>
When the srcutree.convert_to_big and srcutree.big_cpu_lim kernel boot
parameters specify initialization-time allocation of the srcu_node
tree for statically allocated srcu_struct structures (for example, in
DEFINE_SRCU() at build time instead of init_srcu_struct() at runtime),
init_srcu_struct_nodes() will attempt to dynamically allocate this tree
at the first run-time update-side use of this srcu_struct structure,
but while holding a raw spinlock. Because the memory allocator can
acquire non-raw spinlocks, this can result in lockdep splats.
This commit therefore uses the same SRCU_SIZE_ALLOC trick that is used
when the first run-time update-side use of this srcu_struct structure
happens before srcu_init() is called. The actual allocation then takes
place from workqueue context at the ends of upcoming SRCU grace periods.
[boqun: Adjust the sha1 of the Fixes tag]
Fixes: 175b45ed34 ("srcu: Use raw spinlocks so call_srcu() can be used under preempt_disable()")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Tree SRCU has used non-raw spinlocks for many years, motivated by a desire
to avoid unnecessary real-time latency and the absence of any reason to
use raw spinlocks. However, the recent use of SRCU in tracing as the
underlying implementation of RCU Tasks Trace means that call_srcu()
is invoked from preemption-disabled regions of code, which in turn
requires that any locks acquired by call_srcu() or its callees must be
raw spinlocks.
This commit therefore converts SRCU's spinlocks to raw spinlocks.
[boqun: Add Fixes tag]
Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Fixes: c27cea4416 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Linus Torvalds
Frederic Weisbecker
Uladzislau Rezki (Sony)
Arnd Bergmann
Zqiang
Paul E. McKenney
Gustavo Luiz Duarte
Joel Fernandes
Boqun Feng
Kees Cook