kernel/include/linux/sched, branch linux-6.17.y

sched/fair: Get rid of sched_domains_curr_level hack for tl->cpumask()

2025-10-15T10:03:17Z

[ Upstream commit 661f951e371cc134ea31c84238dbdc9a898b8403 ] Leon [1] and Vinicius [2] noted a topology_span_sane() warning during their testing starting from v6.16-rc1. Debug that followed pointed to the tl->mask() for the NODE domain being incorrectly resolved to that of the highest NUMA domain. tl->mask() for NODE is set to the sd_numa_mask() which depends on the global "sched_domains_curr_level" hack. "sched_domains_curr_level" is set to the "tl->numa_level" during tl traversal in build_sched_domains() calling sd_init() but was not reset before topology_span_sane(). Since "tl->numa_level" still reflected the old value from build_sched_domains(), topology_span_sane() for the NODE domain trips when the span of the last NUMA domain overlaps. Instead of replicating the "sched_domains_curr_level" hack, get rid of it entirely and instead, pass the entire "sched_domain_topology_level" object to tl->cpumask() function to prevent such mishap in the future. sd_numa_mask() now directly references "tl->numa_level" instead of relying on the global "sched_domains_curr_level" hack to index into sched_domains_numa_masks[]. The original warning was reproducible on the following NUMA topology reported by Leon: $ sudo numactl -H available: 5 nodes (0-4) node 0 cpus: 0 1 node 0 size: 2927 MB node 0 free: 1603 MB node 1 cpus: 2 3 node 1 size: 3023 MB node 1 free: 3008 MB node 2 cpus: 4 5 node 2 size: 3023 MB node 2 free: 3007 MB node 3 cpus: 6 7 node 3 size: 3023 MB node 3 free: 3002 MB node 4 cpus: 8 9 node 4 size: 3022 MB node 4 free: 2718 MB node distances: node 0 1 2 3 4 0: 10 39 38 37 36 1: 39 10 38 37 36 2: 38 38 10 37 36 3: 37 37 37 10 36 4: 36 36 36 36 10 The above topology can be mimicked using the following QEMU cmd that was used to reproduce the warning and test the fix: sudo qemu-system-x86_64 -enable-kvm -cpu host \ -m 20G -smp cpus=10,sockets=10 -machine q35 \ -object memory-backend-ram,size=4G,id=m0 \ -object memory-backend-ram,size=4G,id=m1 \ -object memory-backend-ram,size=4G,id=m2 \ -object memory-backend-ram,size=4G,id=m3 \ -object memory-backend-ram,size=4G,id=m4 \ -numa node,cpus=0-1,memdev=m0,nodeid=0 \ -numa node,cpus=2-3,memdev=m1,nodeid=1 \ -numa node,cpus=4-5,memdev=m2,nodeid=2 \ -numa node,cpus=6-7,memdev=m3,nodeid=3 \ -numa node,cpus=8-9,memdev=m4,nodeid=4 \ -numa dist,src=0,dst=1,val=39 \ -numa dist,src=0,dst=2,val=38 \ -numa dist,src=0,dst=3,val=37 \ -numa dist,src=0,dst=4,val=36 \ -numa dist,src=1,dst=0,val=39 \ -numa dist,src=1,dst=2,val=38 \ -numa dist,src=1,dst=3,val=37 \ -numa dist,src=1,dst=4,val=36 \ -numa dist,src=2,dst=0,val=38 \ -numa dist,src=2,dst=1,val=38 \ -numa dist,src=2,dst=3,val=37 \ -numa dist,src=2,dst=4,val=36 \ -numa dist,src=3,dst=0,val=37 \ -numa dist,src=3,dst=1,val=37 \ -numa dist,src=3,dst=2,val=37 \ -numa dist,src=3,dst=4,val=36 \ -numa dist,src=4,dst=0,val=36 \ -numa dist,src=4,dst=1,val=36 \ -numa dist,src=4,dst=2,val=36 \ -numa dist,src=4,dst=3,val=36 \ ... [ prateek: Moved common functions to include/linux/sched/topology.h, reuse the common bits for s390 and ppc, commit message ] Closes: https://lore.kernel.org/lkml/20250610110701.GA256154@unreal/ [1] Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap") # ce29a7da84cd, f55dac1dafb3 Signed-off-by: Peter Zijlstra (Intel) Reported-by: Leon Romanovsky Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Shrikanth Hegde Tested-by: Valentin Schneider # x86 Tested-by: Shrikanth Hegde # powerpc Link: https://lore.kernel.org/lkml/a3de98387abad28592e6ab591f3ff6107fe01dc1.1755893468.git.tim.c.chen@linux.intel.com/ [2] Signed-off-by: Sasha Levin

Merge tag 'sched_ext-for-6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext

2025-07-31T23:29:46Z

Pull sched_ext updates from Tejun Heo: - Add support for cgroup "cpu.max" interface - Code organization cleanup so that ext_idle.c doesn't depend on the source-file-inclusion build method of sched/ - Drop UP paths in accordance with sched core changes - Documentation and other misc changes * tag 'sched_ext-for-6.17' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext: sched_ext: Fix scx_bpf_reenqueue_local() reference sched_ext: Drop kfuncs marked for removal in 6.15 sched_ext, rcu: Eject BPF scheduler on RCU CPU stall panic kernel/sched/ext.c: fix typo "occured" -> "occurred" in comments sched_ext: Add support for cgroup bandwidth control interface sched_ext, sched/core: Factor out struct scx_task_group sched_ext: Return NULL in llc_span sched_ext: Always use SMP versions in kernel/sched/ext_idle.h sched_ext: Always use SMP versions in kernel/sched/ext_idle.c sched_ext: Always use SMP versions in kernel/sched/ext.h sched_ext: Always use SMP versions in kernel/sched/ext.c sched_ext: Documentation: Clarify time slice handling in task lifecycle sched_ext: Make scx_locked_rq() inline sched_ext: Make scx_rq_bypassing() inline sched_ext: idle: Make local functions static in ext_idle.c sched_ext: idle: Remove unnecessary ifdef in scx_bpf_cpu_node()

Merge tag 'sched-core-2025-07-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-07-30T00:42:52Z

Pull scheduler updates from Ingo Molnar: "Core scheduler changes: - Better tracking of maximum lag of tasks in presence of different slices duration, for better handling of lag in the fair scheduler (Vincent Guittot) - Clean up and standardize #if/#else/#endif markers throughout the entire scheduler code base (Ingo Molnar) - Make SMP unconditional: build the SMP scheduler's data structures and logic on UP kernel too, even though they are not used, to simplify the scheduler and remove around 200 #ifdef/[#else]/#endif blocks from the scheduler (Ingo Molnar) - Reorganize cgroup bandwidth control interface handling for better interfacing with sched_ext (Tejun Heo) Balancing: - Bump sd->max_newidle_lb_cost when newidle balance fails (Chris Mason) - Remove sched_domain_topology_level::flags to simplify the code (Prateek Nayak) - Simplify and clean up build_sched_topology() (Li Chen) - Optimize build_sched_topology() on large machines (Li Chen) Real-time scheduling: - Add initial version of proxy execution: a mechanism for mutex-owning tasks to inherit the scheduling context of higher priority waiters. Currently limited to a single runqueue and conditional on CONFIG_EXPERT, and other limitations (John Stultz, Peter Zijlstra, Valentin Schneider) - Deadline scheduler (Juri Lelli): - Fix dl_servers initialization order (Juri Lelli) - Fix DL scheduler's root domain reinitialization logic (Juri Lelli) - Fix accounting bugs after global limits change (Juri Lelli) - Fix scalability regression by implementing less agressive dl_server handling (Peter Zijlstra) PSI: - Improve scalability by optimizing psi_group_change() cpu_clock() usage (Peter Zijlstra) Rust changes: - Make Task, CondVar and PollCondVar methods inline to avoid unnecessary function calls (Kunwu Chan, Panagiotis Foliadis) - Add might_sleep() support for Rust code: Rust's "#[track_caller]" mechanism is used so that Rust's might_sleep() doesn't need to be defined as a macro (Fujita Tomonori) - Introduce file_from_location() (Boqun Feng) Debugging & instrumentation: - Make clangd usable with scheduler source code files again (Peter Zijlstra) - tools: Add root_domains_dump.py which dumps root domains info (Juri Lelli) - tools: Add dl_bw_dump.py for printing bandwidth accounting info (Juri Lelli) Misc cleanups & fixes: - Remove play_idle() (Feng Lee) - Fix check_preemption_disabled() (Sebastian Andrzej Siewior) - Do not call __put_task_struct() on RT if pi_blocked_on is set (Luis Claudio R. Goncalves) - Correct the comment in place_entity() (wang wei)" * tag 'sched-core-2025-07-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (84 commits) sched/idle: Remove play_idle() sched: Do not call __put_task_struct() on rt if pi_blocked_on is set sched: Start blocked_on chain processing in find_proxy_task() sched: Fix proxy/current (push,pull)ability sched: Add an initial sketch of the find_proxy_task() function sched: Fix runtime accounting w/ split exec & sched contexts sched: Move update_curr_task logic into update_curr_se locking/mutex: Add p->blocked_on wrappers for correctness checks locking/mutex: Rework task_struct::blocked_on sched: Add CONFIG_SCHED_PROXY_EXEC & boot argument to enable/disable sched/topology: Remove sched_domain_topology_level::flags x86/smpboot: avoid SMT domain attach/destroy if SMT is not enabled x86/smpboot: moves x86_topology to static initialize and truncate x86/smpboot: remove redundant CONFIG_SCHED_SMT smpboot: introduce SDTL_INIT() helper to tidy sched topology setup tools/sched: Add dl_bw_dump.py for printing bandwidth accounting info tools/sched: Add root_domains_dump.py which dumps root domains info sched/deadline: Fix accounting after global limits change sched/deadline: Reset extra_bw to max_bw when clearing root domains sched/deadline: Initialize dl_servers after SMP ...

Merge tag 'locking-futex-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-07-29T21:39:42Z

Pull futex updates from Thomas Gleixner: - Switch the reference counting to a RCU based per-CPU reference to address a performance bottleneck vs the single instance rcuref variant - Make the futex selftest build on 32-bit architectures which only support 64-bit time_t, e.g. RISCV-32 - Cleanups and improvements in selftests and futex bench * tag 'locking-futex-2025-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: selftests/futex: Fix spelling mistake "Succeffuly" -> "Successfully" selftests/futex: Define SYS_futex on 32-bit architectures with 64-bit time_t perf bench futex: Remove support for IMMUTABLE selftests/futex: Remove support for IMMUTABLE futex: Remove support for IMMUTABLE futex: Make futex_private_hash_get() static futex: Use RCU-based per-CPU reference counting instead of rcuref_t selftests/futex: Adapt the private hash test to RCU related changes

sched/task_stack: Add missing const qualifier to end_of_stack()

2025-07-26T21:28:35Z

Add missing const qualifier to the non-CONFIG_THREAD_INFO_IN_TASK version of end_of_stack() to match the CONFIG_THREAD_INFO_IN_TASK version. Fixes a warning with CONFIG_KSTACK_ERASE=y on archs that don't select THREAD_INFO_IN_TASK (such as LoongArch): error: passing 'const struct task_struct *' to parameter of type 'struct task_struct *' discards qualifiers The stackleak_task_low_bound() function correctly uses a const task parameter, but the legacy end_of_stack() prototype didn't like that. Build tested on loongarch (with CONFIG_KSTACK_ERASE=y) and m68k (with CONFIG_DEBUG_STACK_USAGE=y). Fixes: a45728fd4120 ("LoongArch: Enable HAVE_ARCH_STACKLEAK") Reported-by: Nathan Chancellor Closes: https://lore.kernel.org/all/20250726004313.GA3650901@ax162 Cc: Youling Tang Cc: Huacai Chen Tested-by: Nathan Chancellor Signed-off-by: Kees Cook

sched: Do not call __put_task_struct() on rt if pi_blocked_on is set

2025-07-14T15:16:33Z

With PREEMPT_RT enabled, some of the calls to put_task_struct() coming from rt_mutex_adjust_prio_chain() could happen in preemptible context and with a mutex enqueued. That could lead to this sequence: rt_mutex_adjust_prio_chain() put_task_struct() __put_task_struct() sched_ext_free() spin_lock_irqsave() rtlock_lock() ---> TRIGGERS lockdep_assert(!current->pi_blocked_on); This is not a SCHED_EXT bug. The first cleanup function called by __put_task_struct() is sched_ext_free() and it happens to take a (RT) spin_lock, which in the scenario described above, would trigger the lockdep assertion of "!current->pi_blocked_on". Crystal Wood was able to identify the problem as __put_task_struct() being called during rt_mutex_adjust_prio_chain(), in the context of a process with a mutex enqueued. Instead of adding more complex conditions to decide when to directly call __put_task_struct() and when to defer the call, unconditionally resort to the deferred call on PREEMPT_RT to simplify the code. Fixes: 893cdaaa3977 ("sched: avoid false lockdep splat in put_task_struct()") Suggested-by: Crystal Wood Signed-off-by: Luis Claudio R. Goncalves Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Wander Lairson Costa Reviewed-by: Valentin Schneider Reviewed-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/aGvTz5VaPFyj0pBV@uudg.org

sched/topology: Remove sched_domain_topology_level::flags

2025-07-14T08:59:35Z

Support for overlapping domains added in commit e3589f6c81e4 ("sched: Allow for overlapping sched_domain spans") also allowed forcefully setting SD_OVERLAP for !NUMA domains via FORCE_SD_OVERLAP sched_feat(). Since NUMA domains had to be presumed overlapping to ensure correct behavior, "sched_domain_topology_level::flags" was introduced. NUMA domains added the SDTL_OVERLAP flag would ensure SD_OVERLAP was always added during build_sched_domains() for these domains, even when FORCE_SD_OVERLAP was off. Condition for adding the SD_OVERLAP flag at the aforementioned commit was as follows: if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP)) sd->flags |= SD_OVERLAP; The FORCE_SD_OVERLAP debug feature was removed in commit af85596c74de ("sched/topology: Remove FORCE_SD_OVERLAP") which left the NUMA domains as the exclusive users of SDTL_OVERLAP, SD_OVERLAP, and SD_NUMA flags. Get rid of SDTL_OVERLAP and SD_OVERLAP as they have become redundant and instead rely on SD_NUMA to detect the only overlapping domain currently supported. Since SDTL_OVERLAP was the only user of "tl->flags", get rid of "sched_domain_topology_level::flags" too. Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/ba4dbdf8-bc37-493d-b2e0-2efb00ea3e19@amd.com

smpboot: introduce SDTL_INIT() helper to tidy sched topology setup

2025-07-14T08:59:34Z

Define a small SDTL_INIT(maskfn, flagsfn, name) macro and use it to build the sched_domain_topology_level array. Purely a cleanup; behaviour is unchanged. Suggested-by: Thomas Gleixner Signed-off-by: Li Chen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: K Prateek Nayak Tested-by: K Prateek Nayak Link: https://lore.kernel.org/r/20250710105715.66594-2-me@linux.beauty

futex: Use RCU-based per-CPU reference counting instead of rcuref_t

2025-07-11T14:02:00Z

The use of rcuref_t for reference counting introduces a performance bottleneck when accessed concurrently by multiple threads during futex operations. Replace rcuref_t with special crafted per-CPU reference counters. The lifetime logic remains the same. The newly allocate private hash starts in FR_PERCPU state. In this state, each futex operation that requires the private hash uses a per-CPU counter (an unsigned int) for incrementing or decrementing the reference count. When the private hash is about to be replaced, the per-CPU counters are migrated to a atomic_t counter mm_struct::futex_atomic. The migration process: - Waiting for one RCU grace period to ensure all users observe the current private hash. This can be skipped if a grace period elapsed since the private hash was assigned. - futex_private_hash::state is set to FR_ATOMIC, forcing all users to use mm_struct::futex_atomic for reference counting. - After a RCU grace period, all users are guaranteed to be using the atomic counter. The per-CPU counters can now be summed up and added to the atomic_t counter. If the resulting count is zero, the hash can be safely replaced. Otherwise, active users still hold a valid reference. - Once the atomic reference count drops to zero, the next futex operation will switch to the new private hash. call_rcu_hurry() is used to speed up transition which otherwise might be delay with RCU_LAZY. There is nothing wrong with using call_rcu(). The side effects would be that on auto scaling the new hash is used later and the SET_SLOTS prctl() will block longer. [bigeasy: commit description + mm get/ put_async] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250710110011.384614-3-bigeasy@linutronix.de

sched_ext: Drop kfuncs marked for removal in 6.15

2025-06-25T23:13:20Z

sched_ext performed a kfunc renaming pass in 6.13 and kept the old names around for compatibility with old binaries. These were scheduled for cleanup in 6.15 but were missed. Submitting for cleanup in for-next. Removed the kfuncs, their flags, and any references I could find to them in doc comments. Left the entries in include/scx/compat.bpf.h as they're still useful to make new binaries compatible with old kernels. Tested by applying to my kernel. It builds and a modern version of scx_lavd loads fine. Signed-off-by: Jake Hillion Signed-off-by: Tejun Heo