STRUCT RCU_TASKS(9)

💖 NAME 💖

okay bestie, this is the Kernel API Manual page for struct rcu_tasks(9) — literally the definition for a Tasks-RCU-like mechanism. no cap, it's giving kernel-internals realness ✨

✨ SYNOPSIS ✨

here's the whole struct, exactly as it appears, because we do not play with technical accuracy in this group chat 🫶

       struct rcu_tasks {
           struct rcuwait cbs_wait;
           raw_spinlock_t cbs_gbl_lock;
           struct mutex tasks_gp_mutex;
           int gp_state;
           int gp_sleep;
           int init_fract;
           unsigned long gp_jiffies;
           unsigned long gp_start;
           unsigned long tasks_gp_seq;
           unsigned long n_ipis;
           struct task_struct *kthread_ptr;
           unsigned long lazy_jiffies;
           rcu_tasks_gp_func_t gp_func;
           pregp_func_t pregp_func;
           pertask_func_t pertask_func;
           postscan_func_t postscan_func;
           holdouts_func_t holdouts_func;
           postgp_func_t postgp_func;
           call_rcu_func_t call_func;
           unsigned int wait_state;
           struct rcu_tasks_percpu __percpu *rtpcpu;
           struct rcu_tasks_percpu **rtpcp_array;
           int percpu_enqueue_shift;
           int percpu_enqueue_lim;
           int percpu_dequeue_lim;
           unsigned long percpu_dequeue_gpseq;
           struct mutex barrier_q_mutex;
           atomic_t barrier_q_count;
           struct completion barrier_q_completion;
           unsigned long barrier_q_seq;
           unsigned long barrier_q_start;
           char *name;
           char *kname;
        };

🧚 Members 🧚

• cbs_wait — RCU wait allowing a new callback to get kthread's attention. 👀
• cbs_gbl_lock — lock protecting callback list 🔒
• tasks_gp_mutex — mutex protecting grace period, needed during mid-boot dead zone 🫠
• gp_state — grace period's most recent state transition, for debugging 🐛
• gp_sleep — per-grace-period sleep to prevent CPU-bound looping 😴
• init_fract — initial backoff sleep interval ⏳
• gp_jiffies — time of last gp_state transition
• gp_start — most recent grace-period start in jiffies
• tasks_gp_seq — number of grace periods completed since boot in upper bits
• n_ipis — number of IPIs sent to encourage grace periods to end 📣
• kthread_ptr — this flavor's grace-period/callback-invocation kthread 🧵
• lazy_jiffies — number of jiffies to allow callbacks to be lazy 🛋️
• gp_func — this flavor's grace-period-wait function
• pregp_func — this flavor's pre-grace-period function (optional) ✨
• pertask_func — this flavor's per-task scan function (optional)
• postscan_func — this flavor's post-task scan function (optional)
• holdouts_func — this flavor's holdout-list scan function (optional)
• postgp_func — this flavor's post-grace-period function (optional)
• call_func — this flavor's call_rcu-equivalent function
• wait_state — task state for synchronous grace-period waits (default TASK_UNINTERRUPTIBLE) 💤
• rtpcpu — this flavor's rcu_tasks_percpu structure
• rtpcp_array — array of pointers to rcu_tasks_percpu structure of CPUs in cpu_possible_mask
• percpu_enqueue_shift — shift down CPU ID this much when enqueuing callbacks
• percpu_enqueue_lim — number of per-CPU callback queues in use for enqueuing
• percpu_dequeue_lim — number of per-CPU callback queues in use for dequeuing
• percpu_dequeue_gpseq — RCU grace-period number to propagate enqueue limit to dequeuers
• barrier_q_mutex — serialize barrier operations
• barrier_q_count — number of queues being waited on
• barrier_q_completion — barrier wait/wakeup mechanism
• barrier_q_seq — sequence number for barrier operations
• barrier_q_start — most recent barrier start in jiffies
• name — this flavor's textual name
• kname — this flavor's kthread name

🌈 SEE ALSO 🌈

• Kernel file ./kernel/rcu/tasks.h
• struct rcu_tasks_percpu(9)
• call_rcu_tasks(9)
• synchronize_rcu_tasks(9)
• rcu_barrier_tasks(9)
• synchronize_rcu_tasks_rude(9)

byeee 💅 this page came from the ./kernel/rcu source, dated October 2026, and it is literally the struct rcu_tasks(9) manual — mwah 🎀