/* 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; /* One element of the srcu_data srcu_ctrs array. */ struct srcu_ctr { atomic_long_t srcu_locks; /* Locks per CPU. */ atomic_long_t srcu_unlocks; /* Unlocks per CPU. */ }; /* * Per-CPU structure feeding into leaf srcu_node, similar in function * to rcu_node. */ struct srcu_data { /* Read-side state. */ struct srcu_ctr srcu_ctrs[2]; /* Locks and unlocks per CPU. */ int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */ /* Values: SRCU_READ_FLAVOR_.* */ /* Update-side state. */ raw_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 rcu_head srcu_ec_head; /* For srcu_expedite_current() use. */ int srcu_ec_state; /* State for srcu_expedite_current(). */ 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 { raw_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. */ raw_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 irq_work irq_work; struct srcu_struct *srcu_ssp; }; /* * Per-SRCU-domain structure, similar in function to rcu_state. */ struct srcu_struct { struct srcu_ctr __percpu *srcu_ctrp; struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ u8 srcu_reader_flavor; 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 srcu_expedite_current() state (->srcu_ec_state). */ #define SRCU_EC_IDLE 0 #define SRCU_EC_PENDING 1 #define SRCU_EC_REPOST 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 = __RAW_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, fast) \ .srcu_sup = &usage_name, \ .srcu_reader_flavor = fast, \ __SRCU_DEP_MAP_INIT(name) #define __SRCU_STRUCT_INIT_MODULE(name, usage_name, fast) \ { \ __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ } #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name, fast) \ { \ .sda = &pcpu_name, \ .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ } /* * 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. * * DEFINE_SRCU_FAST() and DEFINE_STATIC_SRCU_FAST create an srcu_struct * and associated structures whose readers must be of the SRCU-fast variety. * DEFINE_SRCU_FAST_UPDOWN() and DEFINE_STATIC_SRCU_FAST_UPDOWN() create * an srcu_struct and associated structures whose readers must be of the * SRCU-fast-updown variety. The key point (aside from error checking) with * both varieties is that the grace periods must use synchronize_rcu() * instead of smp_mb(), and given that the first (for example) * srcu_read_lock_fast() might race with the first synchronize_srcu(), * this different must be specified at initialization time. */ #ifdef MODULE # define __DEFINE_SRCU(name, fast, 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, \ fast); \ 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, fast, 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, fast) #endif #define DEFINE_SRCU(name) __DEFINE_SRCU(name, 0, /* not static */) #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, 0, static) #define DEFINE_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, /* not static */) #define DEFINE_STATIC_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, static) #define DEFINE_SRCU_FAST_UPDOWN(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, \ /* not static */) #define DEFINE_STATIC_SRCU_FAST_UPDOWN(name) \ __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, static) int __srcu_read_lock(struct srcu_struct *ssp) __acquires_shared(ssp); void synchronize_srcu_expedited(struct srcu_struct *ssp); void srcu_barrier(struct srcu_struct *ssp); void srcu_expedite_current(struct srcu_struct *ssp); void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); // Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that // element's index. static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp) { return scpp - &ssp->sda->srcu_ctrs[0]; } // Converts an integer to a per-CPU pointer to the corresponding // ->srcu_ctrs[] array element. static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx) { return &ssp->sda->srcu_ctrs[idx]; } /* * Counts the new reader in the appropriate per-CPU element of the * srcu_struct. Returns a pointer that must be passed to the matching * srcu_read_unlock_fast(). * * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side * critical sections either because they disables interrupts, because * they are a single instruction, or because they are read-modify-write * atomic operations, depending on the whims of the architecture. * This matters because the SRCU-fast grace-period mechanism uses either * synchronize_rcu() or synchronize_rcu_expedited(), that is, RCU, * *not* SRCU, in order to eliminate the need for the read-side smp_mb() * invocations that are used by srcu_read_lock() and srcu_read_unlock(). * The __srcu_read_unlock_fast() function also relies on this same RCU * (again, *not* SRCU) trick to eliminate the need for smp_mb(). * * The key point behind this RCU trick is that if any part of a given * RCU reader precedes the beginning of a given RCU grace period, then * the entirety of that RCU reader and everything preceding it happens * before the end of that same RCU grace period. Similarly, if any part * of a given RCU reader follows the end of a given RCU grace period, * then the entirety of that RCU reader and everything following it * happens after the beginning of that same RCU grace period. Therefore, * the operations labeled Y in __srcu_read_lock_fast() and those labeled Z * in __srcu_read_unlock_fast() are ordered against the corresponding SRCU * read-side critical section from the viewpoint of the SRCU grace period. * This is all the ordering that is required, hence no calls to smp_mb(). * * This means that __srcu_read_lock_fast() is not all that fast * on architectures that support NMIs but do not supply NMI-safe * implementations of this_cpu_inc(). */ static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp) __acquires_shared(ssp) { struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. else atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. barrier(); /* Avoid leaking the critical section. */ __acquire_shared(ssp); return scp; } /* * 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_fast(), but it must be within the same task. * * Please see the __srcu_read_lock_fast() function's header comment for * information on implicit RCU readers and NMI safety. */ static inline void notrace __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) __releases_shared(ssp) { __release_shared(ssp); barrier(); /* Avoid leaking the critical section. */ if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. else atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. } /* * Counts the new reader in the appropriate per-CPU element of the * srcu_struct. Returns a pointer that must be passed to the matching * srcu_read_unlock_fast_updown(). This type of reader is compatible * with srcu_down_read_fast() and srcu_up_read_fast(). * * See the __srcu_read_lock_fast() comment for more details. */ static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast_updown(struct srcu_struct *ssp) __acquires_shared(ssp) { struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. else atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. barrier(); /* Avoid leaking the critical section. */ __acquire_shared(ssp); return scp; } /* * 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_fast(), but it must be within the same task. * * Please see the __srcu_read_lock_fast() function's header comment for * information on implicit RCU readers and NMI safety. */ static inline void notrace __srcu_read_unlock_fast_updown(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) __releases_shared(ssp) { __release_shared(ssp); barrier(); /* Avoid leaking the critical section. */ if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. else atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. } void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); // Record SRCU-reader usage type 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
