Pull scheduler fix from Ingo Molnar:
"Revert a scheduler performance optimization that regressed other
workloads"
* tag 'sched-urgent-2025-03-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
Revert "sched/core: Reduce cost of sched_move_task when config autogroup"
This reverts commit eff6c8ce8d.
Hazem reported a 30% drop in UnixBench spawn test with commit
eff6c8ce8d ("sched/core: Reduce cost of sched_move_task when config
autogroup") on a m6g.xlarge AWS EC2 instance with 4 vCPUs and 16 GiB RAM
(aarch64) (single level MC sched domain):
https://lkml.kernel.org/r/20250205151026.13061-1-hagarhem@amazon.com
There is an early bail from sched_move_task() if p->sched_task_group is
equal to p's 'cpu cgroup' (sched_get_task_group()). E.g. both are
pointing to taskgroup '/user.slice/user-1000.slice/session-1.scope'
(Ubuntu '22.04.5 LTS').
So in:
do_exit()
sched_autogroup_exit_task()
sched_move_task()
if sched_get_task_group(p) == p->sched_task_group
return
/* p is enqueued */
dequeue_task() \
sched_change_group() |
task_change_group_fair() |
detach_task_cfs_rq() | (1)
set_task_rq() |
attach_task_cfs_rq() |
enqueue_task() /
(1) isn't called for p anymore.
Turns out that the regression is related to sgs->group_util in
group_is_overloaded() and group_has_capacity(). If (1) isn't called for
all the 'spawn' tasks then sgs->group_util is ~900 and
sgs->group_capacity = 1024 (single CPU sched domain) and this leads to
group_is_overloaded() returning true (2) and group_has_capacity() false
(3) much more often compared to the case when (1) is called.
I.e. there are much more cases of 'group_is_overloaded' and
'group_fully_busy' in WF_FORK wakeup sched_balance_find_dst_cpu() which
then returns much more often a CPU != smp_processor_id() (5).
This isn't good for these extremely short running tasks (FORK + EXIT)
and also involves calling sched_balance_find_dst_group_cpu() unnecessary
(single CPU sched domain).
Instead if (1) is called for 'p->flags & PF_EXITING' then the path
(4),(6) is taken much more often.
select_task_rq_fair(..., wake_flags = WF_FORK)
cpu = smp_processor_id()
new_cpu = sched_balance_find_dst_cpu(..., cpu, ...)
group = sched_balance_find_dst_group(..., cpu)
do {
update_sg_wakeup_stats()
sgs->group_type = group_classify()
if group_is_overloaded() (2)
return group_overloaded
if !group_has_capacity() (3)
return group_fully_busy
return group_has_spare (4)
} while group
if local_sgs.group_type > idlest_sgs.group_type
return idlest (5)
case group_has_spare:
if local_sgs.idle_cpus >= idlest_sgs.idle_cpus
return NULL (6)
Unixbench Tests './Run -c 4 spawn' on:
(a) VM AWS instance (m7gd.16xlarge) with v6.13 ('maxcpus=4 nr_cpus=4')
and Ubuntu 22.04.5 LTS (aarch64).
Shell & test run in '/user.slice/user-1000.slice/session-1.scope'.
w/o patch w/ patch
21005 27120
(b) i7-13700K with tip/sched/core ('nosmt maxcpus=8 nr_cpus=8') and
Ubuntu 22.04.5 LTS (x86_64).
Shell & test run in '/A'.
w/o patch w/ patch
67675 88806
CONFIG_SCHED_AUTOGROUP=y & /sys/proc/kernel/sched_autogroup_enabled equal
0 or 1.
Reported-by: Hazem Mohamed Abuelfotoh <abuehaze@amazon.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Hagar Hemdan <hagarhem@amazon.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250314151345.275739-1-dietmar.eggemann@arm.com
Pull scheduler fix from Ingo Molnar:
"Fix a sleeping-while-atomic bug caused by a recent optimization
utilizing static keys that didn't consider that the
static_key_disable() call could be triggered in atomic context.
Revert the optimization"
* tag 'sched-urgent-2025-03-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/clock: Don't define sched_clock_irqtime as static key
Pull sched_ext fix from Tejun Heo:
"BPF schedulers could trigger a crash by passing in an invalid CPU to
the scx_bpf_select_cpu_dfl() helper.
Fix it by verifying input validity"
* tag 'sched_ext-for-6.14-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Validate prev_cpu in scx_bpf_select_cpu_dfl()
The sched_clock_irqtime was defined as a static key in:
8722903cbb ("sched: Define sched_clock_irqtime as static key")
However, this change introduces a 'sleeping in atomic context' warning:
arch/x86/kernel/tsc.c:1214 mark_tsc_unstable()
warn: sleeping in atomic context
As analyzed by Dan, the affected code path is as follows:
vcpu_load() <- disables preempt
-> kvm_arch_vcpu_load()
-> mark_tsc_unstable() <- sleeps
virt/kvm/kvm_main.c
166 void vcpu_load(struct kvm_vcpu *vcpu)
167 {
168 int cpu = get_cpu();
^^^^^^^^^^
This get_cpu() disables preemption.
169
170 __this_cpu_write(kvm_running_vcpu, vcpu);
171 preempt_notifier_register(&vcpu->preempt_notifier);
172 kvm_arch_vcpu_load(vcpu, cpu);
173 put_cpu();
174 }
arch/x86/kvm/x86.c
4979 if (unlikely(vcpu->cpu != cpu) || kvm_check_tsc_unstable()) {
4980 s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
4981 rdtsc() - vcpu->arch.last_host_tsc;
4982 if (tsc_delta < 0)
4983 mark_tsc_unstable("KVM discovered backwards TSC");
arch/x86/kernel/tsc.c
1206 void mark_tsc_unstable(char *reason)
1207 {
1208 if (tsc_unstable)
1209 return;
1210
1211 tsc_unstable = 1;
1212 if (using_native_sched_clock())
1213 clear_sched_clock_stable();
--> 1214 disable_sched_clock_irqtime();
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
kernel/jump_label.c
245 void static_key_disable(struct static_key *key)
246 {
247 cpus_read_lock();
^^^^^^^^^^^^^^^^
This lock has a might_sleep() in it which triggers the static checker
warning.
248 static_key_disable_cpuslocked(key);
249 cpus_read_unlock();
250 }
Let revert this change for now as {disable,enable}_sched_clock_irqtime
are used in many places, as pointed out by Sean, including the following:
The code path in clocksource_watchdog():
clocksource_watchdog()
|
-> spin_lock(&watchdog_lock);
|
-> __clocksource_unstable()
|
-> clocksource.mark_unstable() == tsc_cs_mark_unstable()
|
-> disable_sched_clock_irqtime()
And the code path in sched_clock_register():
/* Cannot register a sched_clock with interrupts on */
local_irq_save(flags);
...
/* Enable IRQ time accounting if we have a fast enough sched_clock() */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();
local_irq_restore(flags);
[ lkp@intel.com: reported a build error in the prev version ]
[ mingo: cherry-picked it over into sched/urgent ]
Closes: https://lore.kernel.org/kvm/37a79ba3-9ce0-479c-a5b0-2bd75d573ed3@stanley.mountain/
Fixes: 8722903cbb ("sched: Define sched_clock_irqtime as static key")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Debugged-by: Dan Carpenter <dan.carpenter@linaro.org>
Debugged-by: Sean Christopherson <seanjc@google.com>
Debugged-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20250205032438.14668-1-laoar.shao@gmail.com
The ftrace selftest reported a failure because writing -1 to
sched_rt_runtime_us returns -EBUSY. This happens when the possible
CPUs are different from active CPUs.
Active CPUs are part of one root domain, while remaining CPUs are part
of def_root_domain. Since active cpumask is being used, this results in
cpus=0 when a non active CPUs is used in the loop.
Fix it by looping over the online CPUs instead for validating the
bandwidth calculations.
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20250306052954.452005-2-sshegde@linux.ibm.com
child_cfs_rq_on_list attempts to convert a 'prev' pointer to a cfs_rq.
This 'prev' pointer can originate from struct rq's leaf_cfs_rq_list,
making the conversion invalid and potentially leading to memory
corruption. Depending on the relative positions of leaf_cfs_rq_list and
the task group (tg) pointer within the struct, this can cause a memory
fault or access garbage data.
The issue arises in list_add_leaf_cfs_rq, where both
cfs_rq->leaf_cfs_rq_list and rq->leaf_cfs_rq_list are added to the same
leaf list. Also, rq->tmp_alone_branch can be set to rq->leaf_cfs_rq_list.
This adds a check `if (prev == &rq->leaf_cfs_rq_list)` after the main
conditional in child_cfs_rq_on_list. This ensures that the container_of
operation will convert a correct cfs_rq struct.
This check is sufficient because only cfs_rqs on the same CPU are added
to the list, so verifying the 'prev' pointer against the current rq's list
head is enough.
Fixes a potential memory corruption issue that due to current struct
layout might not be manifesting as a crash but could lead to unpredictable
behavior when the layout changes.
Fixes: fdaba61ef8 ("sched/fair: Ensure that the CFS parent is added after unthrottling")
Signed-off-by: Zecheng Li <zecheng@google.com>
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250304214031.2882646-1-zecheng@google.com
If a BPF scheduler provides an invalid CPU (outside the nr_cpu_ids
range) as prev_cpu to scx_bpf_select_cpu_dfl() it can cause a kernel
crash.
To prevent this, validate prev_cpu in scx_bpf_select_cpu_dfl() and
trigger an scx error if an invalid CPU is specified.
Fixes: f0e1a0643a ("sched_ext: Implement BPF extensible scheduler class")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Pull scheduler fix from Ingo Molnar:
"Prevent cond_resched() based preemption when interrupts are disabled,
on PREEMPT_NONE and PREEMPT_VOLUNTARY kernels"
* tag 'sched-urgent-2025-02-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/core: Prevent rescheduling when interrupts are disabled
David reported a warning observed while loop testing kexec jump:
Interrupts enabled after irqrouter_resume+0x0/0x50
WARNING: CPU: 0 PID: 560 at drivers/base/syscore.c:103 syscore_resume+0x18a/0x220
kernel_kexec+0xf6/0x180
__do_sys_reboot+0x206/0x250
do_syscall_64+0x95/0x180
The corresponding interrupt flag trace:
hardirqs last enabled at (15573): [<ffffffffa8281b8e>] __up_console_sem+0x7e/0x90
hardirqs last disabled at (15580): [<ffffffffa8281b73>] __up_console_sem+0x63/0x90
That means __up_console_sem() was invoked with interrupts enabled. Further
instrumentation revealed that in the interrupt disabled section of kexec
jump one of the syscore_suspend() callbacks woke up a task, which set the
NEED_RESCHED flag. A later callback in the resume path invoked
cond_resched() which in turn led to the invocation of the scheduler:
__cond_resched+0x21/0x60
down_timeout+0x18/0x60
acpi_os_wait_semaphore+0x4c/0x80
acpi_ut_acquire_mutex+0x3d/0x100
acpi_ns_get_node+0x27/0x60
acpi_ns_evaluate+0x1cb/0x2d0
acpi_rs_set_srs_method_data+0x156/0x190
acpi_pci_link_set+0x11c/0x290
irqrouter_resume+0x54/0x60
syscore_resume+0x6a/0x200
kernel_kexec+0x145/0x1c0
__do_sys_reboot+0xeb/0x240
do_syscall_64+0x95/0x180
This is a long standing problem, which probably got more visible with
the recent printk changes. Something does a task wakeup and the
scheduler sets the NEED_RESCHED flag. cond_resched() sees it set and
invokes schedule() from a completely bogus context. The scheduler
enables interrupts after context switching, which causes the above
warning at the end.
Quite some of the code paths in syscore_suspend()/resume() can result in
triggering a wakeup with the exactly same consequences. They might not
have done so yet, but as they share a lot of code with normal operations
it's just a question of time.
The problem only affects the PREEMPT_NONE and PREEMPT_VOLUNTARY scheduling
models. Full preemption is not affected as cond_resched() is disabled and
the preemption check preemptible() takes the interrupt disabled flag into
account.
Cure the problem by adding a corresponding check into cond_resched().
Reported-by: David Woodhouse <dwmw@amazon.co.uk>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/all/7717fe2ac0ce5f0a2c43fdab8b11f4483d54a2a4.camel@infradead.org
Pull sched_ext fix from Tejun Heo:
"pick_task_scx() has a workaround to avoid stalling when the fair
class's balance() says yes but pick_task() says no.
The workaround was incorrectly deciding to keep the prev taks running
if the task is on SCX even when the task is in a sleeping state, which
can lead to several confusing failure modes.
Fix it by testing the prev task is currently queued on SCX instead"
* tag 'sched_ext-for-6.14-rc4-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Fix pick_task_scx() picking non-queued tasks when it's called without balance()
a6250aa251 ("sched_ext: Handle cases where pick_task_scx() is called
without preceding balance_scx()") added a workaround to handle the cases
where pick_task_scx() is called without prececing balance_scx() which is due
to a fair class bug where pick_taks_fair() may return NULL after a true
return from balance_fair().
The workaround detects when pick_task_scx() is called without preceding
balance_scx() and emulates SCX_RQ_BAL_KEEP and triggers kicking to avoid
stalling. Unfortunately, the workaround code was testing whether @prev was
on SCX to decide whether to keep the task running. This is incorrect as the
task may be on SCX but no longer runnable.
This could lead to a non-runnable task to be returned from pick_task_scx()
which cause interesting confusions and failures. e.g. A common failure mode
is the task ending up with (!on_rq && on_cpu) state which can cause
potential wakers to busy loop, which can easily lead to deadlocks.
Fix it by testing whether @prev has SCX_TASK_QUEUED set. This makes
@prev_on_scx only used in one place. Open code the usage and improve the
comment while at it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Pat Cody <patcody@meta.com>
Fixes: a6250aa251 ("sched_ext: Handle cases where pick_task_scx() is called without preceding balance_scx()")
Cc: stable@vger.kernel.org # v6.12+
Acked-by: Andrea Righi <arighi@nvidia.com>
When a process reduces its number of threads or clears bits in its CPU
affinity mask, the mm_cid allocation should eventually converge towards
smaller values.
However, the change introduced by:
commit 7e019dcc47 ("sched: Improve cache locality of RSEQ concurrency
IDs for intermittent workloads")
adds a per-mm/CPU recent_cid which is never unset unless a thread
migrates.
This is a tradeoff between:
A) Preserving cache locality after a transition from many threads to few
threads, or after reducing the hamming weight of the allowed CPU mask.
B) Making the mm_cid upper bounds wrt nr threads and allowed CPU mask
easy to document and understand.
C) Allowing applications to eventually react to mm_cid compaction after
reduction of the nr threads or allowed CPU mask, making the tracking
of mm_cid compaction easier by shrinking it back towards 0 or not.
D) Making sure applications that periodically reduce and then increase
again the nr threads or allowed CPU mask still benefit from good
cache locality with mm_cid.
Introduce the following changes:
* After shrinking the number of threads or reducing the number of
allowed CPUs, reduce the value of max_nr_cid so expansion of CID
allocation will preserve cache locality if the number of threads or
allowed CPUs increase again.
* Only re-use a recent_cid if it is within the max_nr_cid upper bound,
else find the first available CID.
Fixes: 7e019dcc47 ("sched: Improve cache locality of RSEQ concurrency IDs for intermittent workloads")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lkml.kernel.org/r/20250210153253.460471-2-gmonaco@redhat.com
Pull scheduler fix from Borislav Petkov:
- Clarify what happens when a task is woken up from the wake queue and
make clear its removal from that queue is atomic
* tag 'sched_urgent_for_v6.14_rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched: Clarify wake_up_q()'s write to task->wake_q.next
Pull sched_ext fixes from Tejun Heo:
- Fix lock imbalance in a corner case of dispatch_to_local_dsq()
- Migration disabled tasks were confusing some BPF schedulers and its
handling had a bug. Fix it and simplify the default behavior by
dispatching them automatically
- ops.tick(), ops.disable() and ops.exit_task() were incorrectly
disallowing kfuncs that require the task argument to be the rq
operation is currently operating on and thus is rq-locked.
Allow them.
- Fix autogroup migration handling bug which was occasionally
triggering a warning in the cgroup migration path
- tools/sched_ext, selftest and other misc updates
* tag 'sched_ext-for-6.14-rc2-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Use SCX_CALL_OP_TASK in task_tick_scx
sched_ext: Fix the incorrect bpf_list kfunc API in common.bpf.h.
sched_ext: selftests: Fix grammar in tests description
sched_ext: Fix incorrect assumption about migration disabled tasks in task_can_run_on_remote_rq()
sched_ext: Fix migration disabled handling in targeted dispatches
sched_ext: Implement auto local dispatching of migration disabled tasks
sched_ext: Fix incorrect time delta calculation in time_delta()
sched_ext: Fix lock imbalance in dispatch_to_local_dsq()
sched_ext: selftests/dsp_local_on: Fix selftest on UP systems
tools/sched_ext: Add helper to check task migration state
sched_ext: Fix incorrect autogroup migration detection
sched_ext: selftests/dsp_local_on: Fix sporadic failures
selftests/sched_ext: Fix enum resolution
sched_ext: Include task weight in the error state dump
sched_ext: Fixes typos in comments
Now when we use scx_bpf_task_cgroup() in ops.tick() to get the cgroup of
the current task, the following error will occur:
scx_foo[3795244] triggered exit kind 1024:
runtime error (called on a task not being operated on)
The reason is that we are using SCX_CALL_OP() instead of SCX_CALL_OP_TASK()
when calling ops.tick(), which triggers the error during the subsequent
scx_kf_allowed_on_arg_tasks() check.
SCX_CALL_OP_TASK() was first introduced in commit 36454023f5 ("sched_ext:
Track tasks that are subjects of the in-flight SCX operation") to ensure
task's rq lock is held when accessing task's sched_group. Since ops.tick()
is marked as SCX_KF_TERMINAL and task_tick_scx() is protected by the rq
lock, we can use SCX_CALL_OP_TASK() to avoid the above issue. Similarly,
the same changes should be made for ops.disable() and ops.exit_task(), as
they are also protected by task_rq_lock() and it's safe to access the
task's task_group.
Fixes: 36454023f5 ("sched_ext: Track tasks that are subjects of the in-flight SCX operation")
Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
While fixing migration disabled task handling, 3296682157 ("sched_ext: Fix
migration disabled handling in targeted dispatches") assumed that a
migration disabled task's ->cpus_ptr would only have the pinned CPU. While
this is eventually true for migration disabled tasks that are switched out,
->cpus_ptr update is performed by migrate_disable_switch() which is called
right before context_switch() in __scheduler(). However, the task is
enqueued earlier during pick_next_task() via put_prev_task_scx(), so there
is a race window where another CPU can see the task on a DSQ.
If the CPU tries to dispatch the migration disabled task while in that
window, task_allowed_on_cpu() will succeed and task_can_run_on_remote_rq()
will subsequently trigger SCHED_WARN(is_migration_disabled()).
WARNING: CPU: 8 PID: 1837 at kernel/sched/ext.c:2466 task_can_run_on_remote_rq+0x12e/0x140
Sched_ext: layered (enabled+all), task: runnable_at=-10ms
RIP: 0010:task_can_run_on_remote_rq+0x12e/0x140
...
<TASK>
consume_dispatch_q+0xab/0x220
scx_bpf_dsq_move_to_local+0x58/0xd0
bpf_prog_84dd17b0654b6cf0_layered_dispatch+0x290/0x1cfa
bpf__sched_ext_ops_dispatch+0x4b/0xab
balance_one+0x1fe/0x3b0
balance_scx+0x61/0x1d0
prev_balance+0x46/0xc0
__pick_next_task+0x73/0x1c0
__schedule+0x206/0x1730
schedule+0x3a/0x160
__do_sys_sched_yield+0xe/0x20
do_syscall_64+0xbb/0x1e0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Fix it by converting the SCHED_WARN() back to a regular failure path. Also,
perform the migration disabled test before task_allowed_on_cpu() test so
that BPF schedulers which fail to handle migration disabled tasks can be
noticed easily.
While at it, adjust scx_ops_error() message for !task_allowed_on_cpu() case
for brevity and consistency.
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 3296682157 ("sched_ext: Fix migration disabled handling in targeted dispatches")
Acked-by: Andrea Righi <arighi@nvidia.com>
Reported-by: Jake Hillion <jakehillion@meta.com>
A dispatch operation that can target a specific local DSQ -
scx_bpf_dsq_move_to_local() or scx_bpf_dsq_move() - checks whether the task
can be migrated to the target CPU using task_can_run_on_remote_rq(). If the
task can't be migrated to the targeted CPU, it is bounced through a global
DSQ.
task_can_run_on_remote_rq() assumes that the task is on a CPU that's
different from the targeted CPU but the callers doesn't uphold the
assumption and may call the function when the task is already on the target
CPU. When such task has migration disabled, task_can_run_on_remote_rq() ends
up returning %false incorrectly unnecessarily bouncing the task to a global
DSQ.
Fix it by updating the callers to only call task_can_run_on_remote_rq() when
the task is on a different CPU than the target CPU. As this is a bit subtle,
for clarity and documentation:
- Make task_can_run_on_remote_rq() trigger SCHED_WARN_ON() if the task is on
the same CPU as the target CPU.
- is_migration_disabled() test in task_can_run_on_remote_rq() cannot trigger
if the task is on a different CPU than the target CPU as the preceding
task_allowed_on_cpu() test should fail beforehand. Convert the test into
SCHED_WARN_ON().
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 4c30f5ce4f ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()")
Fixes: 0366017e09 ("sched_ext: Use task_can_run_on_remote_rq() test in dispatch_to_local_dsq()")
Cc: stable@vger.kernel.org # v6.12+
Migration disabled tasks are special and pinned to their previous CPUs. They
tripped up some unsuspecting BPF schedulers as their ->nr_cpus_allowed may
not agree with the bits set in ->cpus_ptr. Make it easier for BPF schedulers
by automatically dispatching them to the pinned local DSQs by default. If a
BPF scheduler wants to handle migration disabled tasks explicitly, it can
set SCX_OPS_ENQ_MIGRATION_DISABLED.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>
Pull scheduler fixes from Ingo Molnar:
"Fix a cfs_rq->h_nr_runnable accounting bug that trips up a defensive
SCHED_WARN_ON() on certain workloads. The bug is believed to be
(accidentally) self-correcting, hence no behavioral side effects are
expected.
Also print se.slice in debug output, since this value can now be set
via the syscall ABI and can be useful to track"
* tag 'sched-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/debug: Provide slice length for fair tasks
sched/fair: Fix inaccurate h_nr_runnable accounting with delayed dequeue
Pull more power management updates from Rafael Wysocki:
"These are mostly fixes on top of the previously merged power
management material with the addition of some teo cpuidle governor
updates, some of which may also be regarded as fixes:
- Add missing error handling for syscore_suspend() to the hibernation
core code (Wentao Liang)
- Revert a commit that added unused macros (Andy Shevchenko)
- Synchronize the runtime PM status of devices that were runtime-
suspended before a system-wide suspend and need to be resumed
during the subsequent system-wide resume transition (Rafael
Wysocki)
- Clean up the teo cpuidle governor and make the handling of short
idle intervals in it consistent regardless of the properties of
idle states supplied by the cpuidle driver (Rafael Wysocki)
- Fix some boost-related issues in cpufreq (Lifeng Zheng)
- Fix build issues in the s3c64xx and airoha cpufreq drivers (Viresh
Kumar)
- Remove unconditional binding of schedutil governor kthreads to the
affected CPUs if the cpufreq driver indicates that updates can
happen from any CPU (Christian Loehle)"
* tag 'pm-6.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
PM: sleep: core: Synchronize runtime PM status of parents and children
cpufreq: airoha: Depends on OF
PM: Revert "Add EXPORT macros for exporting PM functions"
PM: hibernate: Add error handling for syscore_suspend()
cpufreq/schedutil: Only bind threads if needed
cpufreq: ACPI: Remove set_boost in acpi_cpufreq_cpu_init()
cpufreq: CPPC: Fix wrong max_freq in policy initialization
cpufreq: Introduce a more generic way to set default per-policy boost flag
cpufreq: Fix re-boost issue after hotplugging a CPU
cpufreq: s3c64xx: Fix compilation warning
cpuidle: teo: Skip sleep length computation for low latency constraints
cpuidle: teo: Replace time_span_ns with a flag
cpuidle: teo: Simplify handling of total events count
cpuidle: teo: Skip getting the sleep length if wakeups are very frequent
cpuidle: teo: Simplify counting events used for tick management
cpuidle: teo: Clarify two code comments
cpuidle: teo: Drop local variable prev_intercept_idx
cpuidle: teo: Combine candidate state index checks against 0
cpuidle: teo: Reorder candidate state index checks
cpuidle: teo: Rearrange idle state lookup code
Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.
Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25c ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.
Created this by running an spatch followed by a sed command:
Spatch:
virtual patch
@
depends on !(file in "net")
disable optional_qualifier
@
identifier table_name != {
watchdog_hardlockup_sysctl,
iwcm_ctl_table,
ucma_ctl_table,
memory_allocation_profiling_sysctls,
loadpin_sysctl_table
};
@@
+ const
struct ctl_table table_name [] = { ... };
sed:
sed --in-place \
-e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
kernel/utsname_sysctl.c
Reviewed-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> # for kernel/trace/
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> # SCSI
Reviewed-by: Darrick J. Wong <djwong@kernel.org> # xfs
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>
While performing the rq locking dance in dispatch_to_local_dsq(), we may
trigger the following lock imbalance condition, in particular when
multiple tasks are rapidly changing CPU affinity (i.e., running a
`stress-ng --race-sched 0`):
[ 13.413579] =====================================
[ 13.413660] WARNING: bad unlock balance detected!
[ 13.413729] 6.13.0-virtme #15 Not tainted
[ 13.413792] -------------------------------------
[ 13.413859] kworker/1:1/80 is trying to release lock (&rq->__lock) at:
[ 13.413954] [<ffffffff873c6c48>] dispatch_to_local_dsq+0x108/0x1a0
[ 13.414111] but there are no more locks to release!
[ 13.414176]
[ 13.414176] other info that might help us debug this:
[ 13.414258] 1 lock held by kworker/1:1/80:
[ 13.414318] #0: ffff8b66feb41698 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x20/0x90
[ 13.414612]
[ 13.414612] stack backtrace:
[ 13.415255] CPU: 1 UID: 0 PID: 80 Comm: kworker/1:1 Not tainted 6.13.0-virtme #15
[ 13.415505] Workqueue: 0x0 (events)
[ 13.415567] Sched_ext: dsp_local_on (enabled+all), task: runnable_at=-2ms
[ 13.415570] Call Trace:
[ 13.415700] <TASK>
[ 13.415744] dump_stack_lvl+0x78/0xe0
[ 13.415806] ? dispatch_to_local_dsq+0x108/0x1a0
[ 13.415884] print_unlock_imbalance_bug+0x11b/0x130
[ 13.415965] ? dispatch_to_local_dsq+0x108/0x1a0
[ 13.416226] lock_release+0x231/0x2c0
[ 13.416326] _raw_spin_unlock+0x1b/0x40
[ 13.416422] dispatch_to_local_dsq+0x108/0x1a0
[ 13.416554] flush_dispatch_buf+0x199/0x1d0
[ 13.416652] balance_one+0x194/0x370
[ 13.416751] balance_scx+0x61/0x1e0
[ 13.416848] prev_balance+0x43/0xb0
[ 13.416947] __pick_next_task+0x6b/0x1b0
[ 13.417052] __schedule+0x20d/0x1740
This happens because dispatch_to_local_dsq() is racing with
dispatch_dequeue() and, when the latter wins, we incorrectly assume that
the task has been moved to dst_rq.
Fix by properly tracking the currently locked rq.
Fixes: 4d3ca89bdd ("sched_ext: Refactor consume_remote_task()")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
