kernel/linux.git/include/linux/spinlock.h, branch v6.19.11

spinlock: extend guard with spinlock_bh variants

2025-02-09T10:08:11+00:00

Extend guard APIs with missing raw/spinlock_bh variants. Signed-off-by: Christian Marangi Acked-by: Peter Zijlstra (Intel) Signed-off-by: Herbert Xu

sched/core: Drop spinlocks on contention iff kernel is preemptible

2024-06-05T14:52:36+00:00

Use preempt_model_preemptible() to detect a preemptible kernel when deciding whether or not to reschedule in order to drop a contended spinlock or rwlock. Because PREEMPT_DYNAMIC selects PREEMPTION, kernels built with PREEMPT_DYNAMIC=y will yield contended locks even if the live preemption model is "none" or "voluntary". In short, make kernels with dynamically selected models behave the same as kernels with statically selected models. Somewhat counter-intuitively, NOT yielding a lock can provide better latency for the relevant tasks/processes. E.g. KVM x86's mmu_lock, a rwlock, is often contended between an invalidation event (takes mmu_lock for write) and a vCPU servicing a guest page fault (takes mmu_lock for read). For _some_ setups, letting the invalidation task complete even if there is mmu_lock contention provides lower latency for *all* tasks, i.e. the invalidation completes sooner *and* the vCPU services the guest page fault sooner. But even KVM's mmu_lock behavior isn't uniform, e.g. the "best" behavior can vary depending on the host VMM, the guest workload, the number of vCPUs, the number of pCPUs in the host, why there is lock contention, etc. In other words, simply deleting the CONFIG_PREEMPTION guard (or doing the opposite and removing contention yielding entirely) needs to come with a big pile of data proving that changing the status quo is a net positive. Opportunistically document this side effect of preempt=full, as yielding contended spinlocks can have significant, user-visible impact. Fixes: c597bfddc9e9 ("sched: Provide Kconfig support for default dynamic preempt mode") Signed-off-by: Sean Christopherson Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ankur Arora Reviewed-by: Chen Yu Link: https://lore.kernel.org/kvm/ef81ff36-64bb-4cfe-ae9b-e3acf47bff24@proxmox.com

Merge tag 'header_cleanup-2024-01-20' of https://evilpiepirate.org/git/bcachefs

2024-01-21T18:21:43+00:00

Pull header fix from Kent Overstreet: "Just one small fixup for the RT build" * tag 'header_cleanup-2024-01-20' of https://evilpiepirate.org/git/bcachefs: spinlock: Fix failing build for PREEMPT_RT

spinlock: Fix failing build for PREEMPT_RT

2024-01-15T20:52:12+00:00

Since 1d71b30e1f85 ("sched.h: Move (spin|rwlock)_needbreak() to spinlock.h") build fails for PREEMPT_RT, since there is no definition available of either spin_needbreak() and rwlock_needbreak(). Since it was moved on the mentioned commit, it was placed inside a !PREEMPT_RT part of the code, making it out of reach for an RT kernel. Fix this by moving code it a few lines down so it can be reached by an RT build, where it can also make use of the *_is_contended() definition added by the spinlock_rt.h. Fixes: d1d71b30e1f85 ("sched.h: Move (spin|rwlock)_needbreak() to spinlock.h") Signed-off-by: Leonardo Bras Signed-off-by: Kent Overstreet Acked-by: Waiman Long

Merge tag 'header_cleanup-2024-01-10' of https://evilpiepirate.org/git/bcachefs

2024-01-11T00:43:55+00:00

Pull header cleanups from Kent Overstreet: "The goal is to get sched.h down to a type only header, so the main thing happening in this patchset is splitting out various _types.h headers and dependency fixups, as well as moving some things out of sched.h to better locations. This is prep work for the memory allocation profiling patchset which adds new sched.h interdepencencies" * tag 'header_cleanup-2024-01-10' of https://evilpiepirate.org/git/bcachefs: (51 commits) Kill sched.h dependency on rcupdate.h kill unnecessary thread_info.h include Kill unnecessary kernel.h include preempt.h: Kill dependency on list.h rseq: Split out rseq.h from sched.h LoongArch: signal.c: add header file to fix build error restart_block: Trim includes lockdep: move held_lock to lockdep_types.h sem: Split out sem_types.h uidgid: Split out uidgid_types.h seccomp: Split out seccomp_types.h refcount: Split out refcount_types.h uapi/linux/resource.h: fix include x86/signal: kill dependency on time.h syscall_user_dispatch.h: split out *_types.h mm_types_task.h: Trim dependencies Split out irqflags_types.h ipc: Kill bogus dependency on spinlock.h shm: Slim down dependencies workqueue: Split out workqueue_types.h ...

sched.h: Move (spin|rwlock)_needbreak() to spinlock.h

2023-12-21T00:26:30+00:00

This lets us kill the dependency on spinlock.h. Signed-off-by: Kent Overstreet

ptrace: Convert ptrace_attach() to use lock guards

2023-11-29T14:43:54+00:00

Created as testing for the conditional guard infrastructure. Specifically this makes use of the following form: scoped_cond_guard (mutex_intr, return -ERESTARTNOINTR, &task->signal->cred_guard_mutex) { ... } ... return 0; Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Oleg Nesterov Link: https://lkml.kernel.org/r/20231102110706.568467727%40infradead.org

cleanup: Add conditional guard support

2023-11-15T09:15:33+00:00

Adds: - DEFINE_GUARD_COND() / DEFINE_LOCK_GUARD_1_COND() to extend existing guards with conditional lock primitives, eg. mutex_trylock(), mutex_lock_interruptible(). nb. both primitives allow NULL 'locks', which cause the lock to fail (obviously). - extends scoped_guard() to not take the body when the the conditional guard 'fails'. eg. scoped_guard (mutex_intr, &task->signal_cred_guard_mutex) { ... } will only execute the body when the mutex is held. - provides scoped_cond_guard(name, fail, args...); which extends scoped_guard() to do fail when the lock-acquire fails. Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20231102110706.460851167%40infradead.org

locking: Introduce __cleanup() based infrastructure

2023-06-26T09:14:18+00:00

Use __attribute__((__cleanup__(func))) to build: - simple auto-release pointers using __free() - 'classes' with constructor and destructor semantics for scope-based resource management. - lock guards based on the above classes. Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230612093537.614161713%40infradead.org

perf: Fix perf_event_pmu_context serialization

2023-01-31T19:37:18+00:00

Syzkaller triggered a WARN in put_pmu_ctx(). WARNING: CPU: 1 PID: 2245 at kernel/events/core.c:4925 put_pmu_ctx+0x1f0/0x278 This is because there is no locking around the access of "if (!epc->ctx)" in find_get_pmu_context() and when it is set to NULL in put_pmu_ctx(). The decrement of the reference count in put_pmu_ctx() also happens outside of the spinlock, leading to the possibility of this order of events, and the context being cleared in put_pmu_ctx(), after its refcount is non zero: CPU0 CPU1 find_get_pmu_context() if (!epc->ctx) == false put_pmu_ctx() atomic_dec_and_test(&epc->refcount) == true epc->refcount == 0 atomic_inc(&epc->refcount); epc->refcount == 1 list_del_init(&epc->pmu_ctx_entry); epc->ctx = NULL; Another issue is that WARN_ON for no active PMU events in put_pmu_ctx() is outside of the lock. If the perf_event_pmu_context is an embedded one, even after clearing it, it won't be deleted and can be re-used. So the warning can trigger. For this reason it also needs to be moved inside the lock. The above warning is very quick to trigger on Arm by running these two commands at the same time: while true; do perf record -- ls; done while true; do perf record -- ls; done [peterz: atomic_dec_and_raw_lock*()] Fixes: bd2756811766 ("perf: Rewrite core context handling") Reported-by: syzbot+697196bc0265049822bd@syzkaller.appspotmail.com Signed-off-by: James Clark Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Ravi Bangoria Link: https://lore.kernel.org/r/20230127143141.1782804-2-james.clark@arm.com