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/* SPDX-License-Identifier: GPL-2.0+ */ /* * Sleepable Read-Copy Update mechanism for mutual exclusion, * tree variant. * * Copyright (C) IBM Corporation, 2017 * * Author: Paul McKenney <paulmck@linux.ibm.com> */ #ifndef _LINUX_SRCU_TREE_H #define _LINUX_SRCU_TREE_H #include <linux/rcu_node_tree.h> #include <linux/completion.h> struct srcu_node; struct srcu_struct; /* * Per-CPU structure feeding into leaf srcu_node, similar in function * to rcu_node. */ struct srcu_data { /* Read-side state. */ atomic_long_t srcu_lock_count[2]; /* Locks per CPU. */ atomic_long_t srcu_unlock_count[2]; /* Unlocks per CPU. */ int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */ /* Values: SRCU_READ_FLAVOR_.* */ /* Update-side state. */ spinlock_t __private lock ____cacheline_internodealigned_in_smp; struct rcu_segcblist srcu_cblist; /* List of callbacks.*/ unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ bool srcu_cblist_invoking; /* Invoking these CBs? */ struct timer_list delay_work; /* Delay for CB invoking */ struct work_struct work; /* Context for CB invoking. */ struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */ struct srcu_node *mynode; /* Leaf srcu_node. */ unsigned long grpmask; /* Mask for leaf srcu_node */ /* ->srcu_data_have_cbs[]. */ int cpu; struct srcu_struct *ssp; }; /* * Node in SRCU combining tree, similar in function to rcu_data. */ struct srcu_node { spinlock_t __private lock; unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */ /* if greater than ->srcu_gp_seq. */ unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ struct srcu_node *srcu_parent; /* Next up in tree. */ int grplo; /* Least CPU for node. */ int grphi; /* Biggest CPU for node. */ }; /* * Per-SRCU-domain structure, update-side data linked from srcu_struct. */ struct srcu_usage { struct srcu_node *node; /* Combining tree. */ struct srcu_node *level[RCU_NUM_LVLS + 1]; /* First node at each level. */ int srcu_size_state; /* Small-to-big transition state. */ struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ spinlock_t __private lock; /* Protect counters and size state. */ struct mutex srcu_gp_mutex; /* Serialize GP work. */ unsigned long srcu_gp_seq; /* Grace-period seq #. */ unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */ unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */ unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */ unsigned long srcu_n_lock_retries; /* Contention events in current interval. */ unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */ bool sda_is_static; /* May ->sda be passed to free_percpu()? */ unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */ struct completion srcu_barrier_completion; /* Awaken barrier rq at end. */ atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */ /* callback for the barrier */ /* operation. */ unsigned long reschedule_jiffies; unsigned long reschedule_count; struct delayed_work work; struct srcu_struct *srcu_ssp; }; /* * Per-SRCU-domain structure, similar in function to rcu_state. */ struct srcu_struct { unsigned int srcu_idx; /* Current rdr array element. */ struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ struct lockdep_map dep_map; struct srcu_usage *srcu_sup; /* Update-side data. */ }; // Values for size state variable (->srcu_size_state). Once the state // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through // this state machine one step per grace period until the SRCU_SIZE_BIG state // is reached. Otherwise, the state machine remains in the SRCU_SIZE_SMALL // state indefinitely. #define SRCU_SIZE_SMALL 0 // No srcu_node combining tree, ->node == NULL #define SRCU_SIZE_ALLOC 1 // An srcu_node tree is being allocated, initialized, // and then referenced by ->node. It will not be used. #define SRCU_SIZE_WAIT_BARRIER 2 // The srcu_node tree starts being used by everything // except call_srcu(), especially by srcu_barrier(). // By the end of this state, all CPUs and threads // are aware of this tree's existence. #define SRCU_SIZE_WAIT_CALL 3 // The srcu_node tree starts being used by call_srcu(). // By the end of this state, all of the call_srcu() // invocations that were running on a non-boot CPU // and using the boot CPU's callback queue will have // completed. #define SRCU_SIZE_WAIT_CBS1 4 // Don't trust the ->srcu_have_cbs[] grace-period #define SRCU_SIZE_WAIT_CBS2 5 // sequence elements or the ->srcu_data_have_cbs[] #define SRCU_SIZE_WAIT_CBS3 6 // CPU-bitmask elements until all four elements of #define SRCU_SIZE_WAIT_CBS4 7 // each array have been initialized. #define SRCU_SIZE_BIG 8 // The srcu_node combining tree is fully initialized // and all aspects of it are being put to use. /* Values for state variable (bottom bits of ->srcu_gp_seq). */ #define SRCU_STATE_IDLE 0 #define SRCU_STATE_SCAN1 1 #define SRCU_STATE_SCAN2 2 /* * Values for initializing gp sequence fields. Higher values allow wrap arounds to * occur earlier. * The second value with state is useful in the case of static initialization of * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its * lower bits (or else it will appear to be already initialized within * the call check_init_srcu_struct()). */ #define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT) #define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1) #define __SRCU_USAGE_INIT(name) \ { \ .lock = __SPIN_LOCK_UNLOCKED(name.lock), \ .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \ .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \ .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \ .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \ } #define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ .srcu_sup = &usage_name, \ __SRCU_DEP_MAP_INIT(name) #define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \ { \ __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ } #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ { \ .sda = &pcpu_name, \ __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ } /* * Define and initialize a srcu struct at build time. * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. * * Note that although DEFINE_STATIC_SRCU() hides the name from other * files, the per-CPU variable rules nevertheless require that the * chosen name be globally unique. These rules also prohibit use of * DEFINE_STATIC_SRCU() within a function. If these rules are too * restrictive, declare the srcu_struct manually. For example, in * each file: * * static struct srcu_struct my_srcu; * * Then, before the first use of each my_srcu, manually initialize it: * * init_srcu_struct(&my_srcu); * * See include/linux/percpu-defs.h for the rules on per-CPU variables. */ #ifdef MODULE # define __DEFINE_SRCU(name, is_static) \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ extern struct srcu_struct * const __srcu_struct_##name; \ struct srcu_struct * const __srcu_struct_##name \ __section("___srcu_struct_ptrs") = &name #else # define __DEFINE_SRCU(name, is_static) \ static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ is_static struct srcu_struct name = \ __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) #endif #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) void synchronize_srcu_expedited(struct srcu_struct *ssp); void srcu_barrier(struct srcu_struct *ssp); void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); /* * Counts the new reader in the appropriate per-CPU element of the * srcu_struct. Returns an index that must be passed to the matching * srcu_read_unlock_lite(). * * Note that this_cpu_inc() is an RCU read-side critical section either * because it disables interrupts, because it is a single instruction, * or because it is a read-modify-write atomic operation, depending on * the whims of the architecture. */ static inline int __srcu_read_lock_lite(struct srcu_struct *ssp) { int idx; RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite()."); idx = READ_ONCE(ssp->srcu_idx) & 0x1; this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */ barrier(); /* Avoid leaking the critical section. */ return idx; } /* * Removes the count for the old reader from the appropriate * per-CPU element of the srcu_struct. Note that this may well be a * different CPU than that which was incremented by the corresponding * srcu_read_lock_lite(), but it must be within the same task. * * Note that this_cpu_inc() is an RCU read-side critical section either * because it disables interrupts, because it is a single instruction, * or because it is a read-modify-write atomic operation, depending on * the whims of the architecture. */ static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) { barrier(); /* Avoid leaking the critical section. */ this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter); /* Z */ RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite()."); } void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); // Record _lite() usage even for CONFIG_PROVE_RCU=n kernels. static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp) { struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE)) return; // Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered. __srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE); } // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels. static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) { if (IS_ENABLED(CONFIG_PROVE_RCU)) __srcu_check_read_flavor(ssp, read_flavor); } #endif