linux/kernel/sched, branch v6.18

Merge tag 'sched_ext-for-6.18-rc6-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

2025-11-20T19:04:37Z

Pull sched_ext fix from Tejun Heo: "One low risk and obvious fix: scx_enable() was dereferencing an error pointer on helper kthread creation failure. Fixed" * tag 'sched_ext-for-6.18-rc6-fixes-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext: sched_ext: Fix scx_enable() crash on helper kthread creation failure

sched_ext: Fix scx_enable() crash on helper kthread creation failure

2025-11-20T18:45:43Z

A crash was observed when the sched_ext selftests runner was terminated with Ctrl+\ while test 15 was running: NIP [c00000000028fa58] scx_enable.constprop.0+0x358/0x12b0 LR [c00000000028fa2c] scx_enable.constprop.0+0x32c/0x12b0 Call Trace: scx_enable.constprop.0+0x32c/0x12b0 (unreliable) bpf_struct_ops_link_create+0x18c/0x22c __sys_bpf+0x23f8/0x3044 sys_bpf+0x2c/0x6c system_call_exception+0x124/0x320 system_call_vectored_common+0x15c/0x2ec kthread_run_worker() returns an ERR_PTR() on failure rather than NULL, but the current code in scx_alloc_and_add_sched() only checks for a NULL helper. Incase of failure on SIGQUIT, the error is not handled in scx_alloc_and_add_sched() and scx_enable() ends up dereferencing an error pointer. Error handling is fixed in scx_alloc_and_add_sched() to propagate PTR_ERR() into ret, so that scx_enable() jumps to the existing error path, avoiding random dereference on failure. Fixes: bff3b5aec1b7 ("sched_ext: Move disable machinery into scx_sched") Cc: stable@vger.kernel.org # v6.16+ Reported-and-tested-by: Samir Mulani Signed-off-by: Saket Kumar Bhaskar Reviewed-by: Emil Tsalapatis Reviewed-by: Andrea Righi Reviewed-by: Vishal Chourasia Signed-off-by: Tejun Heo

Merge tag 'sched_ext-for-6.18-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

2025-11-17T17:01:22Z

Pull sched_ext fixes from Tejun Heo: "Five fixes addressing PREEMPT_RT compatibility and locking issues. Three commits fix potential deadlocks and sleeps in atomic contexts on RT kernels by converting locks to raw spinlocks and ensuring IRQ work runs in hard-irq context. The remaining two fix unsafe locking in the debug dump path and a variable dereference typo" * tag 'sched_ext-for-6.18-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext: sched_ext: Use IRQ_WORK_INIT_HARD() to initialize rq->scx.kick_cpus_irq_work sched_ext: Fix possible deadlock in the deferred_irq_workfn() sched/ext: convert scx_tasks_lock to raw spinlock sched_ext: Fix unsafe locking in the scx_dump_state() sched_ext: Fix use of uninitialized variable in scx_bpf_cpuperf_set()

sched_ext: Use IRQ_WORK_INIT_HARD() to initialize rq->scx.kick_cpus_irq_work

2025-11-17T15:07:22Z

For PREEMPT_RT kernels, the kick_cpus_irq_workfn() be invoked in the per-cpu irq_work/* task context and there is no rcu-read critical section to protect. this commit therefore use IRQ_WORK_INIT_HARD() to initialize the per-cpu rq->scx.kick_cpus_irq_work in the init_sched_ext_class(). Signed-off-by: Zqiang Signed-off-by: Tejun Heo

sched_ext: Fix possible deadlock in the deferred_irq_workfn()

2025-11-13T18:29:28Z

For PREEMPT_RT=y kernels, the deferred_irq_workfn() is executed in the per-cpu irq_work/* task context and not disable-irq, if the rq returned by container_of() is current CPU's rq, the following scenarios may occur: lock(&rq->__lock); lock(&rq->__lock); This commit use IRQ_WORK_INIT_HARD() to replace init_irq_work() to initialize rq->scx.deferred_irq_work, make the deferred_irq_workfn() is always invoked in hard-irq context. Signed-off-by: Zqiang Signed-off-by: Tejun Heo

sched/ext: convert scx_tasks_lock to raw spinlock

2025-11-12T18:42:02Z

Update scx_task_locks so that it's safe to lock/unlock in a non-sleepable context in PREEMPT_RT kernels. scx_task_locks is (non-raw) spinlock used to protect the list of tasks under SCX. This list is updated during from finish_task_switch(), which cannot sleep. Regular spinlocks can be locked in such a context in non-RT kernels, but are sleepable under when CONFIG_PREEMPT_RT=y. Convert scx_task_locks into a raw spinlock, which is not sleepable even on RT kernels. Sample backtrace: dump_stack_lvl+0x83/0xa0 __might_resched+0x14a/0x200 rt_spin_lock+0x61/0x1c0 ? sched_ext_dead+0x2d/0xf0 ? lock_release+0xc6/0x280 sched_ext_dead+0x2d/0xf0 ? srso_alias_return_thunk+0x5/0xfbef5 finish_task_switch.isra.0+0x254/0x360 __schedule+0x584/0x11d0 ? srso_alias_return_thunk+0x5/0xfbef5 ? srso_alias_return_thunk+0x5/0xfbef5 ? tick_nohz_idle_exit+0x7e/0x120 schedule_idle+0x23/0x40 cpu_startup_entry+0x29/0x30 start_secondary+0xf8/0x100 common_startup_64+0x13e/0x148 Signed-off-by: Emil Tsalapatis Signed-off-by: Tejun Heo

sched_ext: Fix unsafe locking in the scx_dump_state()

2025-11-12T16:28:32Z

For built with CONFIG_PREEMPT_RT=y kernels, the dump_lock will be converted sleepable spinlock and not disable-irq, so the following scenarios occur: inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. irq_work/0/27 [HC0[0]:SC0[0]:HE1:SE1] takes: (&rq->__lock){?...}-{2:2}, at: raw_spin_rq_lock_nested+0x2b/0x40 {IN-HARDIRQ-W} state was registered at: lock_acquire+0x1e1/0x510 _raw_spin_lock_nested+0x42/0x80 raw_spin_rq_lock_nested+0x2b/0x40 sched_tick+0xae/0x7b0 update_process_times+0x14c/0x1b0 tick_periodic+0x62/0x1f0 tick_handle_periodic+0x48/0xf0 timer_interrupt+0x55/0x80 __handle_irq_event_percpu+0x20a/0x5c0 handle_irq_event_percpu+0x18/0xc0 handle_irq_event+0xb5/0x150 handle_level_irq+0x220/0x460 __common_interrupt+0xa2/0x1e0 common_interrupt+0xb0/0xd0 asm_common_interrupt+0x2b/0x40 _raw_spin_unlock_irqrestore+0x45/0x80 __setup_irq+0xc34/0x1a30 request_threaded_irq+0x214/0x2f0 hpet_time_init+0x3e/0x60 x86_late_time_init+0x5b/0xb0 start_kernel+0x308/0x410 x86_64_start_reservations+0x1c/0x30 x86_64_start_kernel+0x96/0xa0 common_startup_64+0x13e/0x148 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&rq->__lock); lock(&rq->__lock); *** DEADLOCK *** stack backtrace: CPU: 0 UID: 0 PID: 27 Comm: irq_work/0 Call Trace: dump_stack_lvl+0x8c/0xd0 dump_stack+0x14/0x20 print_usage_bug+0x42e/0x690 mark_lock.part.44+0x867/0xa70 ? __pfx_mark_lock.part.44+0x10/0x10 ? string_nocheck+0x19c/0x310 ? number+0x739/0x9f0 ? __pfx_string_nocheck+0x10/0x10 ? __pfx_check_pointer+0x10/0x10 ? kvm_sched_clock_read+0x15/0x30 ? sched_clock_noinstr+0xd/0x20 ? local_clock_noinstr+0x1c/0xe0 __lock_acquire+0xc4b/0x62b0 ? __pfx_format_decode+0x10/0x10 ? __pfx_string+0x10/0x10 ? __pfx___lock_acquire+0x10/0x10 ? __pfx_vsnprintf+0x10/0x10 lock_acquire+0x1e1/0x510 ? raw_spin_rq_lock_nested+0x2b/0x40 ? __pfx_lock_acquire+0x10/0x10 ? dump_line+0x12e/0x270 ? raw_spin_rq_lock_nested+0x20/0x40 _raw_spin_lock_nested+0x42/0x80 ? raw_spin_rq_lock_nested+0x2b/0x40 raw_spin_rq_lock_nested+0x2b/0x40 scx_dump_state+0x3b3/0x1270 ? finish_task_switch+0x27e/0x840 scx_ops_error_irq_workfn+0x67/0x80 irq_work_single+0x113/0x260 irq_work_run_list.part.3+0x44/0x70 run_irq_workd+0x6b/0x90 ? __pfx_run_irq_workd+0x10/0x10 smpboot_thread_fn+0x529/0x870 ? __pfx_smpboot_thread_fn+0x10/0x10 kthread+0x305/0x3f0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x40/0x70 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 This commit therefore use rq_lock_irqsave/irqrestore() to replace rq_lock/unlock() in the scx_dump_state(). Fixes: 07814a9439a3 ("sched_ext: Print debug dump after an error exit") Signed-off-by: Zqiang Signed-off-by: Tejun Heo

sched/fair: Prevent cfs_rq from being unthrottled with zero runtime_remaining

2025-11-06T11:30:52Z

When a cfs_rq is to be throttled, its limbo list should be empty and that's why there is a warn in tg_throttle_down() for non empty cfs_rq->throttled_limbo_list. When running a test with the following hierarchy: root / \ A* ... / | \ ... B / \ C* where both A and C have quota settings, that warn on non empty limbo list is triggered for a cfs_rq of C, let's call it cfs_rq_c(and ignore the cpu part of the cfs_rq for the sake of simpler representation). Debug showed it happened like this: Task group C is created and quota is set, so in tg_set_cfs_bandwidth(), cfs_rq_c is initialized with runtime_enabled set, runtime_remaining equals to 0 and *unthrottled*. Before any tasks are enqueued to cfs_rq_c, *multiple* throttled tasks can migrate to cfs_rq_c (e.g., due to task group changes). When enqueue_task_fair(cfs_rq_c, throttled_task) is called and cfs_rq_c is in a throttled hierarchy (e.g., A is throttled), these throttled tasks are directly placed into cfs_rq_c's limbo list by enqueue_throttled_task(). Later, when A is unthrottled, tg_unthrottle_up(cfs_rq_c) enqueues these tasks. The first enqueue triggers check_enqueue_throttle(), and with zero runtime_remaining, cfs_rq_c can be throttled in throttle_cfs_rq() if it can't get more runtime and enters tg_throttle_down(), where the warning is hit due to remaining tasks in the limbo list. I think it's a chaos to trigger throttle on unthrottle path, the status of a being unthrottled cfs_rq can be in a mixed state in the end, so fix this by granting 1ns to cfs_rq in tg_set_cfs_bandwidth(). This ensures cfs_rq_c has a positive runtime_remaining when initialized as unthrottled and cannot enter tg_unthrottle_up() with zero runtime_remaining. Also, update outdated comments in tg_throttle_down() since unthrottle_cfs_rq() is no longer called with zero runtime_remaining. While at it, remove a redundant assignment to se in tg_throttle_down(). Fixes: e1fad12dcb66 ("sched/fair: Switch to task based throttle model") Reviewed-By: Benjamin Segall Suggested-by: Benjamin Segall Signed-off-by: Aaron Lu Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: K Prateek Nayak Tested-by: K Prateek Nayak Tested-by: Hao Jia Link: https://patch.msgid.link/20251030032755.560-1-ziqianlu@bytedance.com

sched_ext: Fix use of uninitialized variable in scx_bpf_cpuperf_set()

2025-10-29T15:14:39Z

scx_bpf_cpuperf_set() has a typo where it dereferences the local variable @sch, instead of the global @scx_root pointer. Fix by dereferencing the correct variable. Fixes: 956f2b11a8a4f ("sched_ext: Drop kf_cpu_valid()") Signed-off-by: Andrea Righi Reviewed-by: Christian Loehle Signed-off-by: Tejun Heo

Merge tag 'sched_ext-for-6.18-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

2025-10-27T17:52:18Z

Pull sched_ext fixes from Tejun Heo: - Fix scx_kick_pseqs corruption when multiple schedulers are loaded concurrently - Allocate scx_kick_cpus_pnt_seqs lazily using kvzalloc() to handle systems with large CPU counts - Defer queue_balance_callback() until after ops.dispatch to fix callback ordering issues - Sync error_irq_work before freeing scx_sched to prevent use-after-free - Mark scx_bpf_dsq_move_set_[slice|vtime]() with KF_RCU for proper RCU protection - Fix flag check for deferred callbacks * tag 'sched_ext-for-6.18-rc3-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext: sched_ext: fix flag check for deferred callbacks sched_ext: Fix scx_kick_pseqs corruption on concurrent scheduler loads sched_ext: Allocate scx_kick_cpus_pnt_seqs lazily using kvzalloc() sched_ext: defer queue_balance_callback() until after ops.dispatch sched_ext: Sync error_irq_work before freeing scx_sched sched_ext: Mark scx_bpf_dsq_move_set_[slice|vtime]() with KF_RCU