diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcu/tree.c | 301 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 9 | ||||
| -rw-r--r-- | kernel/rcu/tree_exp.h | 153 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 297 |
4 files changed, 291 insertions, 469 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 61c15de884b0..5f79315f094e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -92,24 +92,29 @@ static const char *tp_##sname##_varname __used __tracepoint_string = sname##_var #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \ DEFINE_RCU_TPS(sname) \ -static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \ -struct rcu_state sname##_state = { \ - .level = { &sname##_state.node[0] }, \ - .rda = &sname##_data, \ +static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data); \ +struct rcu_state rcu_state = { \ + .level = { &rcu_state.node[0] }, \ + .rda = &rcu_data, \ .call = cr, \ .gp_state = RCU_GP_IDLE, \ .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, \ - .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ + .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex), \ .name = RCU_STATE_NAME(sname), \ .abbr = sabbr, \ - .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \ - .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \ - .ofl_lock = __SPIN_LOCK_UNLOCKED(sname##_state.ofl_lock), \ + .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex), \ + .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), \ + .ofl_lock = __SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock), \ } -RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); +#ifdef CONFIG_PREEMPT_RCU +RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); +#else +RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu); +#endif -static struct rcu_state *const rcu_state_p; +static struct rcu_state *const rcu_state_p = &rcu_state; +static struct rcu_data __percpu *const rcu_data_p = &rcu_data; LIST_HEAD(rcu_struct_flavors); /* Dump rcu_node combining tree at boot to verify correct setup. */ @@ -220,31 +225,9 @@ static int rcu_gp_in_progress(struct rcu_state *rsp) return rcu_seq_state(rcu_seq_current(&rsp->gp_seq)); } -/* - * Note a quiescent state. Because we do not need to know - * how many quiescent states passed, just if there was at least - * one since the start of the grace period, this just sets a flag. - * The caller must have disabled preemption. - */ -void rcu_sched_qs(void) -{ - RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!"); - if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s)) - return; - trace_rcu_grace_period(TPS("rcu_sched"), - __this_cpu_read(rcu_sched_data.gp_seq), - TPS("cpuqs")); - __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false); - if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) - return; - __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false); - rcu_report_exp_rdp(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); -} - void rcu_softirq_qs(void) { - rcu_sched_qs(); - rcu_preempt_qs(); + rcu_qs(); rcu_preempt_deferred_qs(current); } @@ -418,31 +401,18 @@ static void rcu_momentary_dyntick_idle(void) rcu_preempt_deferred_qs(current); } -/* - * Note a context switch. This is a quiescent state for RCU-sched, - * and requires special handling for preemptible RCU. - * The caller must have disabled interrupts. +/** + * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle + * + * If the current CPU is idle or running at a first-level (not nested) + * interrupt from idle, return true. The caller must have at least + * disabled preemption. */ -void rcu_note_context_switch(bool preempt) +static int rcu_is_cpu_rrupt_from_idle(void) { - barrier(); /* Avoid RCU read-side critical sections leaking down. */ - trace_rcu_utilization(TPS("Start context switch")); - rcu_sched_qs(); - rcu_preempt_note_context_switch(preempt); - /* Load rcu_urgent_qs before other flags. */ - if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) - goto out; - this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); - if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) - rcu_momentary_dyntick_idle(); - this_cpu_inc(rcu_dynticks.rcu_qs_ctr); - if (!preempt) - rcu_tasks_qs(current); -out: - trace_rcu_utilization(TPS("End context switch")); - barrier(); /* Avoid RCU read-side critical sections leaking up. */ + return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 && + __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1; } -EXPORT_SYMBOL_GPL(rcu_note_context_switch); /* * Register a quiescent state for all RCU flavors. If there is an @@ -476,8 +446,8 @@ void rcu_all_qs(void) rcu_momentary_dyntick_idle(); local_irq_restore(flags); } - if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) - rcu_sched_qs(); + if (unlikely(raw_cpu_read(rcu_data.cpu_no_qs.b.exp))) + rcu_qs(); this_cpu_inc(rcu_dynticks.rcu_qs_ctr); barrier(); /* Avoid RCU read-side critical sections leaking up. */ preempt_enable(); @@ -558,7 +528,7 @@ EXPORT_SYMBOL_GPL(rcu_get_gp_seq); */ unsigned long rcu_sched_get_gp_seq(void) { - return READ_ONCE(rcu_sched_state.gp_seq); + return rcu_get_gp_seq(); } EXPORT_SYMBOL_GPL(rcu_sched_get_gp_seq); @@ -590,7 +560,7 @@ EXPORT_SYMBOL_GPL(rcu_exp_batches_completed); */ unsigned long rcu_exp_batches_completed_sched(void) { - return rcu_sched_state.expedited_sequence; + return rcu_state.expedited_sequence; } EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched); @@ -617,7 +587,7 @@ EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); */ void rcu_sched_force_quiescent_state(void) { - force_quiescent_state(&rcu_sched_state); + rcu_force_quiescent_state(); } EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); @@ -668,10 +638,8 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, switch (test_type) { case RCU_FLAVOR: case RCU_BH_FLAVOR: - rsp = rcu_state_p; - break; case RCU_SCHED_FLAVOR: - rsp = &rcu_sched_state; + rsp = rcu_state_p; break; default: break; @@ -1107,19 +1075,6 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ -/** - * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle - * - * If the current CPU is idle or running at a first-level (not nested) - * interrupt from idle, return true. The caller must have at least - * disabled preemption. - */ -static int rcu_is_cpu_rrupt_from_idle(void) -{ - return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 && - __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1; -} - /* * We are reporting a quiescent state on behalf of some other CPU, so * it is our responsibility to check for and handle potential overflow @@ -2364,7 +2319,7 @@ rcu_report_unblock_qs_rnp(struct rcu_state *rsp, struct rcu_node *rnp_p; raw_lockdep_assert_held_rcu_node(rnp); - if (WARN_ON_ONCE(rcu_state_p == &rcu_sched_state) || + if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT)) || WARN_ON_ONCE(rsp != rcu_state_p) || WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) || rnp->qsmask != 0) { @@ -2650,25 +2605,7 @@ void rcu_check_callbacks(int user) { trace_rcu_utilization(TPS("Start scheduler-tick")); increment_cpu_stall_ticks(); - if (user || rcu_is_cpu_rrupt_from_idle()) { - - /* - * Get here if this CPU took its interrupt from user - * mode or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. - * - * No memory barrier is required here because - * rcu_sched_qs() references only CPU-local variables - * that other CPUs neither access nor modify, at least - * not while the corresponding CPU is online. - */ - - rcu_sched_qs(); - rcu_note_voluntary_context_switch(current); - - } - rcu_preempt_check_callbacks(); + rcu_flavor_check_callbacks(user); if (rcu_pending()) invoke_rcu_core(); @@ -2694,7 +2631,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp)) mask = 0; raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->qsmask == 0) { - if (rcu_state_p == &rcu_sched_state || + if (!IS_ENABLED(CONFIG_PREEMPT) || rsp != rcu_state_p || rcu_preempt_blocked_readers_cgp(rnp)) { /* @@ -3028,28 +2965,56 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, } /** - * call_rcu_sched() - Queue an RCU for invocation after sched grace period. + * call_rcu() - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * * The callback function will be invoked some time after a full grace - * period elapses, in other words after all currently executing RCU - * read-side critical sections have completed. call_rcu_sched() assumes - * that the read-side critical sections end on enabling of preemption - * or on voluntary preemption. - * RCU read-side critical sections are delimited by: - * - * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR - * - anything that disables preemption. - * - * These may be nested. + * period elapses, in other words after all pre-existing RCU read-side + * critical sections have completed. However, the callback function + * might well execute concurrently with RCU read-side critical sections + * that started after call_rcu() was invoked. RCU read-side critical + * sections are delimited by rcu_read_lock() and rcu_read_unlock(), and + * may be nested. In addition, regions of code across which interrupts, + * preemption, or softirqs have been disabled also serve as RCU read-side + * critical sections. This includes hardware interrupt handlers, softirq + * handlers, and NMI handlers. + * + * Note that all CPUs must agree that the grace period extended beyond + * all pre-existing RCU read-side critical section. On systems with more + * than one CPU, this means that when "func()" is invoked, each CPU is + * guaranteed to have executed a full memory barrier since the end of its + * last RCU read-side critical section whose beginning preceded the call + * to call_rcu(). It also means that each CPU executing an RCU read-side + * critical section that continues beyond the start of "func()" must have + * executed a memory barrier after the call_rcu() but before the beginning + * of that RCU read-side critical section. Note that these guarantees + * include CPUs that are offline, idle, or executing in user mode, as + * well as CPUs that are executing in the kernel. + * + * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the + * resulting RCU callback function "func()", then both CPU A and CPU B are + * guaranteed to execute a full memory barrier during the time interval + * between the call to call_rcu() and the invocation of "func()" -- even + * if CPU A and CPU B are the same CPU (but again only if the system has + * more than one CPU). + */ +void call_rcu(struct rcu_head *head, rcu_callback_t func) +{ + __call_rcu(head, func, rcu_state_p, -1, 0); +} +EXPORT_SYMBOL_GPL(call_rcu); + +/** + * call_rcu_sched() - Queue an RCU for invocation after sched grace period. + * @head: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period * - * See the description of call_rcu() for more detailed information on - * memory ordering guarantees. + * This is transitional. */ void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) { - __call_rcu(head, func, &rcu_sched_state, -1, 0); + call_rcu(head, func); } EXPORT_SYMBOL_GPL(call_rcu_sched); @@ -3067,73 +3032,14 @@ void kfree_call_rcu(struct rcu_head *head, } EXPORT_SYMBOL_GPL(kfree_call_rcu); -/* - * Because a context switch is a grace period for RCU-sched, any blocking - * grace-period wait automatically implies a grace period if there - * is only one CPU online at any point time during execution of either - * synchronize_sched() or synchronize_rcu_bh(). It is OK to occasionally - * incorrectly indicate that there are multiple CPUs online when there - * was in fact only one the whole time, as this just adds some overhead: - * RCU still operates correctly. - */ -static int rcu_blocking_is_gp(void) -{ - int ret; - - might_sleep(); /* Check for RCU read-side critical section. */ - preempt_disable(); - ret = num_online_cpus() <= 1; - preempt_enable(); - return ret; -} - /** * synchronize_sched - wait until an rcu-sched grace period has elapsed. * - * Control will return to the caller some time after a full rcu-sched - * grace period has elapsed, in other words after all currently executing - * rcu-sched read-side critical sections have completed. These read-side - * critical sections are delimited by rcu_read_lock_sched() and - * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), - * local_irq_disable(), and so on may be used in place of - * rcu_read_lock_sched(). - * - * This means that all preempt_disable code sequences, including NMI and - * non-threaded hardware-interrupt handlers, in progress on entry will - * have completed before this primitive returns. However, this does not - * guarantee that softirq handlers will have completed, since in some - * kernels, these handlers can run in process context, and can block. - * - * Note that this guarantee implies further memory-ordering guarantees. - * On systems with more than one CPU, when synchronize_sched() returns, - * each CPU is guaranteed to have executed a full memory barrier since the - * end of its last RCU-sched read-side critical section whose beginning - * preceded the call to synchronize_sched(). In addition, each CPU having - * an RCU read-side critical section that extends beyond the return from - * synchronize_sched() is guaranteed to have executed a full memory barrier - * after the beginning of synchronize_sched() and before the beginning of - * that RCU read-side critical section. Note that these guarantees include - * CPUs that are offline, idle, or executing in user mode, as well as CPUs - * that are executing in the kernel. - * - * Furthermore, if CPU A invoked synchronize_sched(), which returned - * to its caller on CPU B, then both CPU A and CPU B are guaranteed - * to have executed a full memory barrier during the execution of - * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but - * again only if the system has more than one CPU). + * This is transitional. */ void synchronize_sched(void) { - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_sched() in RCU-sched read-side critical section"); - if (rcu_blocking_is_gp()) - return; - if (rcu_gp_is_expedited()) - synchronize_sched_expedited(); - else - wait_rcu_gp(call_rcu_sched); + synchronize_rcu(); } EXPORT_SYMBOL_GPL(synchronize_sched); @@ -3181,41 +3087,23 @@ EXPORT_SYMBOL_GPL(cond_synchronize_rcu); /** * get_state_synchronize_sched - Snapshot current RCU-sched state * - * Returns a cookie that is used by a later call to cond_synchronize_sched() - * to determine whether or not a full grace period has elapsed in the - * meantime. + * This is transitional, and only used by rcutorture. */ unsigned long get_state_synchronize_sched(void) { - /* - * Any prior manipulation of RCU-protected data must happen - * before the load from ->gp_seq. - */ - smp_mb(); /* ^^^ */ - return rcu_seq_snap(&rcu_sched_state.gp_seq); + return get_state_synchronize_rcu(); } EXPORT_SYMBOL_GPL(get_state_synchronize_sched); /** * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period - * * @oldstate: return value from earlier call to get_state_synchronize_sched() * - * If a full RCU-sched grace period has elapsed since the earlier call to - * get_state_synchronize_sched(), just return. Otherwise, invoke - * synchronize_sched() to wait for a full grace period. - * - * Yes, this function does not take counter wrap into account. But - * counter wrap is harmless. If the counter wraps, we have waited for - * more than 2 billion grace periods (and way more on a 64-bit system!), - * so waiting for one additional grace period should be just fine. + * This is transitional and only used by rcutorture. */ void cond_synchronize_sched(unsigned long oldstate) { - if (!rcu_seq_done(&rcu_sched_state.gp_seq, oldstate)) - synchronize_sched(); - else - smp_mb(); /* Ensure GP ends before subsequent accesses. */ + cond_synchronize_rcu(oldstate); } EXPORT_SYMBOL_GPL(cond_synchronize_sched); @@ -3453,11 +3341,27 @@ void rcu_barrier_bh(void) EXPORT_SYMBOL_GPL(rcu_barrier_bh); /** + * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. + * + * Note that this primitive does not necessarily wait for an RCU grace period + * to complete. For example, if there are no RCU callbacks queued anywhere + * in the system, then rcu_barrier() is within its rights to return + * immediately, without waiting for anything, much less an RCU grace period. + */ +void rcu_barrier(void) +{ + _rcu_barrier(rcu_state_p); +} +EXPORT_SYMBOL_GPL(rcu_barrier); + +/** * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. + * + * This is transitional. */ void rcu_barrier_sched(void) { - _rcu_barrier(&rcu_sched_state); + rcu_barrier(); } EXPORT_SYMBOL_GPL(rcu_barrier_sched); @@ -3756,7 +3660,7 @@ void rcu_report_dead(unsigned int cpu) /* QS for any half-done expedited RCU-sched GP. */ preempt_disable(); - rcu_report_exp_rdp(&rcu_sched_state, this_cpu_ptr(rcu_sched_state.rda)); + rcu_report_exp_rdp(&rcu_state, this_cpu_ptr(rcu_state.rda)); preempt_enable(); rcu_preempt_deferred_qs(current); for_each_rcu_flavor(rsp) @@ -4098,10 +4002,9 @@ void __init rcu_init(void) rcu_bootup_announce(); rcu_init_geometry(); - rcu_init_one(&rcu_sched_state); + rcu_init_one(&rcu_state); if (dump_tree) - rcu_dump_rcu_node_tree(&rcu_sched_state); - __rcu_init_preempt(); + rcu_dump_rcu_node_tree(&rcu_state); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index e02c882861eb..38658ca87dcb 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -225,9 +225,6 @@ struct rcu_data { /* 5) _rcu_barrier(), OOM callbacks, and expediting. */ struct rcu_head barrier_head; -#ifdef CONFIG_RCU_FAST_NO_HZ - struct rcu_head oom_head; -#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ int exp_dynticks_snap; /* Double-check need for IPI. */ /* 6) Callback offloading. */ @@ -433,8 +430,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work); /* Forward declarations for rcutree_plugin.h */ static void rcu_bootup_announce(void); -static void rcu_preempt_qs(void); -static void rcu_preempt_note_context_switch(bool preempt); +static void rcu_qs(void); static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU static bool rcu_preempt_has_tasks(struct rcu_node *rnp); @@ -444,9 +440,8 @@ static int rcu_print_task_stall(struct rcu_node *rnp); static int rcu_print_task_exp_stall(struct rcu_node *rnp); static void rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp); -static void rcu_preempt_check_callbacks(void); +static void rcu_flavor_check_callbacks(int user); void call_rcu(struct rcu_head *head, rcu_callback_t func); -static void __init __rcu_init_preempt(void); static void dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck); static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 0f8f225c1b46..5619edfd414e 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -265,7 +265,7 @@ static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp) rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, true); } -/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */ +/* Common code for work-done checking. */ static bool sync_exp_work_done(struct rcu_state *rsp, unsigned long s) { if (rcu_exp_gp_seq_done(rsp, s)) { @@ -337,45 +337,6 @@ fastpath: return false; } -/* Invoked on each online non-idle CPU for expedited quiescent state. */ -static void sync_sched_exp_handler(void *data) -{ - struct rcu_data *rdp; - struct rcu_node *rnp; - struct rcu_state *rsp = data; - - rdp = this_cpu_ptr(rsp->rda); - rnp = rdp->mynode; - if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || - __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)) - return; - if (rcu_is_cpu_rrupt_from_idle()) { - rcu_report_exp_rdp(&rcu_sched_state, - this_cpu_ptr(&rcu_sched_data)); - return; - } - __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true); - /* Store .exp before .rcu_urgent_qs. */ - smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true); - resched_cpu(smp_processor_id()); -} - -/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ -static void sync_sched_exp_online_cleanup(int cpu) -{ - struct rcu_data *rdp; - int ret; - struct rcu_node *rnp; - struct rcu_state *rsp = &rcu_sched_state; - - rdp = per_cpu_ptr(rsp->rda, cpu); - rnp = rdp->mynode; - if (!(READ_ONCE(rnp->expmask) & rdp->grpmask)) - return; - ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0); - WARN_ON_ONCE(ret); -} - /* * Select the CPUs within the specified rcu_node that the upcoming * expedited grace period needs to wait for. @@ -691,39 +652,6 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp, mutex_unlock(&rsp->exp_mutex); } -/** - * synchronize_sched_expedited - Brute-force RCU-sched grace period - * - * Wait for an RCU-sched grace period to elapse, but use a "big hammer" - * approach to force the grace period to end quickly. This consumes - * significant time on all CPUs and is unfriendly to real-time workloads, - * so is thus not recommended for any sort of common-case code. In fact, - * if you are using synchronize_sched_expedited() in a loop, please - * restructure your code to batch your updates, and then use a single - * synchronize_sched() instead. - * - * This implementation can be thought of as an application of sequence - * locking to expedited grace periods, but using the sequence counter to - * determine when someone else has already done the work instead of for - * retrying readers. - */ -void synchronize_sched_expedited(void) -{ - struct rcu_state *rsp = &rcu_sched_state; - - RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || - lock_is_held(&rcu_lock_map) || - lock_is_held(&rcu_sched_lock_map), - "Illegal synchronize_sched_expedited() in RCU read-side critical section"); - - /* If only one CPU, this is automatically a grace period. */ - if (rcu_blocking_is_gp()) - return; - - _synchronize_rcu_expedited(rsp, sync_sched_exp_handler); -} -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); - #ifdef CONFIG_PREEMPT_RCU /* @@ -801,6 +729,11 @@ static void sync_rcu_exp_handler(void *info) resched_cpu(rdp->cpu); } +/* PREEMPT=y, so no RCU-sched to clean up after. */ +static void sync_sched_exp_online_cleanup(int cpu) +{ +} + /** * synchronize_rcu_expedited - Brute-force RCU grace period * @@ -818,6 +751,8 @@ static void sync_rcu_exp_handler(void *info) * you are using synchronize_rcu_expedited() in a loop, please restructure * your code to batch your updates, and then Use a single synchronize_rcu() * instead. + * + * This has the same semantics as (but is more brutal than) synchronize_rcu(). */ void synchronize_rcu_expedited(void) { @@ -836,13 +771,79 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); #else /* #ifdef CONFIG_PREEMPT_RCU */ +/* Invoked on each online non-idle CPU for expedited quiescent state. */ +static void sync_sched_exp_handler(void *data) +{ + struct rcu_data *rdp; + struct rcu_node *rnp; + struct rcu_state *rsp = data; + + rdp = this_cpu_ptr(rsp->rda); + rnp = rdp->mynode; + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || + __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) + return; + if (rcu_is_cpu_rrupt_from_idle()) { + rcu_report_exp_rdp(&rcu_state, this_cpu_ptr(&rcu_data)); + return; + } + __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true); + /* Store .exp before .rcu_urgent_qs. */ + smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true); + resched_cpu(smp_processor_id()); +} + +/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */ +static void sync_sched_exp_online_cleanup(int cpu) +{ + struct rcu_data *rdp; + int ret; + struct rcu_node *rnp; + struct rcu_state *rsp = &rcu_state; + + rdp = per_cpu_ptr(rsp->rda, cpu); + rnp = rdp->mynode; + if (!(READ_ONCE(rnp->expmask) & rdp->grpmask)) + return; + ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0); + WARN_ON_ONCE(ret); +} + /* - * Wait for an rcu-preempt grace period, but make it happen quickly. - * But because preemptible RCU does not exist, map to rcu-sched. + * Because a context switch is a grace period for RCU-sched, any blocking + * grace-period wait automatically implies a grace period if there + * is only one CPU online at any point time during execution of either + * synchronize_sched() or synchronize_rcu_bh(). It is OK to occasionally + * incorrectly indicate that there are multiple CPUs online when there + * was in fact only one the whole time, as this just adds some overhead: + * RCU still operates correctly. */ +static int rcu_blocking_is_gp(void) +{ + int ret; + + might_sleep(); /* Check for RCU read-side critical section. */ + preempt_disable(); + ret = num_online_cpus() <= 1; + preempt_enable(); + return ret; +} + +/* PREEMPT=n implementation of synchronize_rcu_expedited(). */ void synchronize_rcu_expedited(void) { - synchronize_sched_expedited(); + struct rcu_state *rsp = &rcu_state; + + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_sched_expedited() in RCU read-side critical section"); + + /* If only one CPU, this is automatically a grace period. */ + if (rcu_blocking_is_gp()) + return; + + _synchronize_rcu_expedited(rsp, sync_sched_exp_handler); } EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 9f0d054e6c20..2c81f8dd63b4 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -123,10 +123,6 @@ static void __init rcu_bootup_announce_oddness(void) #ifdef CONFIG_PREEMPT_RCU -RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); -static struct rcu_state *const rcu_state_p = &rcu_preempt_state; -static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; - static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, bool wake); static void rcu_read_unlock_special(struct task_struct *t); @@ -303,15 +299,15 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * * Callers to this function must disable preemption. */ -static void rcu_preempt_qs(void) +static void rcu_qs(void) { - RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n"); + RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n"); if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) { trace_rcu_grace_period(TPS("rcu_preempt"), __this_cpu_read(rcu_data_p->gp_seq), TPS("cpuqs")); __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false); - barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ + barrier(); /* Coordinate with rcu_flavor_check_callbacks(). */ current->rcu_read_unlock_special.b.need_qs = false; } } @@ -329,12 +325,14 @@ static void rcu_preempt_qs(void) * * Caller must disable interrupts. */ -static void rcu_preempt_note_context_switch(bool preempt) +void rcu_note_context_switch(bool preempt) { struct task_struct *t = current; struct rcu_data *rdp = this_cpu_ptr(rcu_state_p->rda); struct rcu_node *rnp; + barrier(); /* Avoid RCU read-side critical sections leaking down. */ + trace_rcu_utilization(TPS("Start context switch")); lockdep_assert_irqs_disabled(); WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); if (t->rcu_read_lock_nesting > 0 && @@ -381,10 +379,13 @@ static void rcu_preempt_note_context_switch(bool preempt) * grace period, then the fact that the task has been enqueued * means that we continue to block the current grace period. */ - rcu_preempt_qs(); + rcu_qs(); if (rdp->deferred_qs) rcu_report_exp_rdp(rcu_state_p, rdp); + trace_rcu_utilization(TPS("End context switch")); + barrier(); /* Avoid RCU read-side critical sections leaking up. */ } +EXPORT_SYMBOL_GPL(rcu_note_context_switch); /* * Check for preempted RCU readers blocking the current grace period @@ -493,7 +494,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) return; } if (special.b.need_qs) { - rcu_preempt_qs(); + rcu_qs(); t->rcu_read_unlock_special.b.need_qs = false; if (!t->rcu_read_unlock_special.s && !rdp->deferred_qs) { local_irq_restore(flags); @@ -596,7 +597,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) */ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) { - return (this_cpu_ptr(&rcu_preempt_data)->deferred_qs || + return (this_cpu_ptr(&rcu_data)->deferred_qs || READ_ONCE(t->rcu_read_unlock_special.s)) && t->rcu_read_lock_nesting <= 0; } @@ -781,11 +782,14 @@ rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) * * Caller must disable hard irqs. */ -static void rcu_preempt_check_callbacks(void) +static void rcu_flavor_check_callbacks(int user) { - struct rcu_state *rsp = &rcu_preempt_state; + struct rcu_state *rsp = &rcu_state; struct task_struct *t = current; + if (user || rcu_is_cpu_rrupt_from_idle()) { + rcu_note_voluntary_context_switch(current); + } if (t->rcu_read_lock_nesting > 0 || (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { /* No QS, force context switch if deferred. */ @@ -795,7 +799,7 @@ static void rcu_preempt_check_callbacks(void) rcu_preempt_deferred_qs(t); /* Report deferred QS. */ return; } else if (!t->rcu_read_lock_nesting) { - rcu_preempt_qs(); /* Report immediate QS. */ + rcu_qs(); /* Report immediate QS. */ return; } @@ -809,44 +813,6 @@ static void rcu_preempt_check_callbacks(void) } /** - * call_rcu() - Queue an RCU callback for invocation after a grace period. - * @head: structure to be used for queueing the RCU updates. - * @func: actual callback function to be invoked after the grace period - * - * The callback function will be invoked some time after a full grace - * period elapses, in other words after all pre-existing RCU read-side - * critical sections have completed. However, the callback function - * might well execute concurrently with RCU read-side critical sections - * that started after call_rcu() was invoked. RCU read-side critical - * sections are delimited by rcu_read_lock() and rcu_read_unlock(), - * and may be nested. - * - * Note that all CPUs must agree that the grace period extended beyond - * all pre-existing RCU read-side critical section. On systems with more - * than one CPU, this means that when "func()" is invoked, each CPU is - * guaranteed to have executed a full memory barrier since the end of its - * last RCU read-side critical section whose beginning preceded the call - * to call_rcu(). It also means that each CPU executing an RCU read-side - * critical section that continues beyond the start of "func()" must have - * executed a memory barrier after the call_rcu() but before the beginning - * of that RCU read-side critical section. Note that these guarantees - * include CPUs that are offline, idle, or executing in user mode, as - * well as CPUs that are executing in the kernel. - * - * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the - * resulting RCU callback function "func()", then both CPU A and CPU B are - * guaranteed to execute a full memory barrier during the time interval - * between the call to call_rcu() and the invocation of "func()" -- even - * if CPU A and CPU B are the same CPU (but again only if the system has - * more than one CPU). - */ -void call_rcu(struct rcu_head *head, rcu_callback_t func) -{ - __call_rcu(head, func, rcu_state_p, -1, 0); -} -EXPORT_SYMBOL_GPL(call_rcu); - -/** * synchronize_rcu - wait until a grace period has elapsed. * * Control will return to the caller some time after a full grace @@ -856,14 +822,28 @@ EXPORT_SYMBOL_GPL(call_rcu); * concurrently with new RCU read-side critical sections that began while * synchronize_rcu() was waiting. RCU read-side critical sections are * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. + * In addition, regions of code across which interrupts, preemption, or + * softirqs have been disabled also serve as RCU read-side critical + * sections. This includes hardware interrupt handlers, softirq handlers, + * and NMI handlers. + * + * Note that this guarantee implies further memory-ordering guarantees. + * On systems with more than one CPU, when synchronize_rcu() returns, + * each CPU is guaranteed to have executed a full memory barrier since the + * end of its last RCU-sched read-side critical section whose beginning + * preceded the call to synchronize_rcu(). In addition, each CPU having + * an RCU read-side critical section that extends beyond the return from + * synchronize_rcu() is guaranteed to have executed a full memory barrier + * after the beginning of synchronize_rcu() and before the beginning of + * that RCU read-side critical section. Note that these guarantees include + * CPUs that are offline, idle, or executing in user mode, as well as CPUs + * that are executing in the kernel. * - * See the description of synchronize_sched() for more detailed - * information on memory-ordering guarantees. However, please note - * that -only- the memory-ordering guarantees apply. For example, - * synchronize_rcu() is -not- guaranteed to wait on things like code - * protected by preempt_disable(), instead, synchronize_rcu() is -only- - * guaranteed to wait on RCU read-side critical sections, that is, sections - * of code protected by rcu_read_lock(). + * Furthermore, if CPU A invoked synchronize_rcu(), which returned + * to its caller on CPU B, then both CPU A and CPU B are guaranteed + * to have executed a full memory barrier during the execution of + * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but + * again only if the system has more than one CPU). */ void synchronize_rcu(void) { @@ -880,28 +860,6 @@ void synchronize_rcu(void) } EXPORT_SYMBOL_GPL(synchronize_rcu); -/** - * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. - * - * Note that this primitive does not necessarily wait for an RCU grace period - * to complete. For example, if there are no RCU callbacks queued anywhere - * in the system, then rcu_barrier() is within its rights to return - * immediately, without waiting for anything, much less an RCU grace period. - */ -void rcu_barrier(void) -{ - _rcu_barrier(rcu_state_p); -} -EXPORT_SYMBOL_GPL(rcu_barrier); - -/* - * Initialize preemptible RCU's state structures. - */ -static void __init __rcu_init_preempt(void) -{ - rcu_init_one(rcu_state_p); -} - /* * Check for a task exiting while in a preemptible-RCU read-side * critical section, clean up if so. No need to issue warnings, @@ -964,8 +922,6 @@ dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck) #else /* #ifdef CONFIG_PREEMPT_RCU */ -static struct rcu_state *const rcu_state_p = &rcu_sched_state; - /* * Tell them what RCU they are running. */ @@ -975,18 +931,48 @@ static void __init rcu_bootup_announce(void) rcu_bootup_announce_oddness(); } -/* Because preemptible RCU does not exist, we can ignore its QSes. */ -static void rcu_preempt_qs(void) +/* + * Note a quiescent state for PREEMPT=n. Because we do not need to know + * how many quiescent states passed, just if there was at least one since + * the start of the grace period, this just sets a flag. The caller must + * have disabled preemption. + */ +static void rcu_qs(void) { + RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!"); + if (!__this_cpu_read(rcu_data.cpu_no_qs.s)) + return; + trace_rcu_grace_period(TPS("rcu_sched"), + __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs")); + __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); + if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) + return; + __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false); + rcu_report_exp_rdp(&rcu_state, this_cpu_ptr(&rcu_data)); } /* - * Because preemptible RCU does not exist, we never have to check for - * CPUs being in quiescent states. + * Note a PREEMPT=n context switch. The caller must have disabled interrupts. */ -static void rcu_preempt_note_context_switch(bool preempt) +void rcu_note_context_switch(bool preempt) { + barrier(); /* Avoid RCU read-side critical sections leaking down. */ + trace_rcu_utilization(TPS("Start context switch")); + rcu_qs(); + /* Load rcu_urgent_qs before other flags. */ + if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) + goto out; + this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); + if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) + rcu_momentary_dyntick_idle(); + this_cpu_inc(rcu_dynticks.rcu_qs_ctr); + if (!preempt) + rcu_tasks_qs(current); +out: + trace_rcu_utilization(TPS("End context switch")); + barrier(); /* Avoid RCU read-side critical sections leaking up. */ } +EXPORT_SYMBOL_GPL(rcu_note_context_switch); /* * Because preemptible RCU does not exist, there are never any preempted @@ -1054,29 +1040,48 @@ rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) } /* - * Because preemptible RCU does not exist, it never has any callbacks - * to check. + * Check to see if this CPU is in a non-context-switch quiescent state + * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). + * Also schedule RCU core processing. + * + * This function must be called from hardirq context. It is normally + * invoked from the scheduling-clock interrupt. */ -static void rcu_preempt_check_callbacks(void) +static void rcu_flavor_check_callbacks(int user) { -} + if (user || rcu_is_cpu_rrupt_from_idle()) { -/* - * Because preemptible RCU does not exist, rcu_barrier() is just - * another name for rcu_barrier_sched(). - */ -void rcu_barrier(void) -{ - rcu_barrier_sched(); + /* + * Get here if this CPU took its interrupt from user + * mode or from the idle loop, and if this is not a + * nested interrupt. In this case, the CPU is in + * a quiescent state, so note it. + * + * No memory barrier is required here because rcu_qs() + * references only CPU-local variables that other CPUs + * neither access nor modify, at least not while the + * corresponding CPU is online. + */ + + rcu_qs(); + } } -EXPORT_SYMBOL_GPL(rcu_barrier); -/* - * Because preemptible RCU does not exist, it need not be initialized. - */ -static void __init __rcu_init_preempt(void) +/* PREEMPT=n implementation of synchronize_rcu(). */ +void synchronize_rcu(void) { + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu() in RCU-sched read-side critical section"); + if (rcu_blocking_is_gp()) + return; + if (rcu_gp_is_expedited()) + synchronize_rcu_expedited(); + else + wait_rcu_gp(call_rcu); } +EXPORT_SYMBOL_GPL(synchronize_rcu); /* * Because preemptible RCU does not exist, tasks cannot possibly exit @@ -1319,8 +1324,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, static void rcu_kthread_do_work(void) { - rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); - rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data)); + rcu_do_batch(&rcu_state, this_cpu_ptr(&rcu_data)); } static void rcu_cpu_kthread_setup(unsigned int cpu) @@ -1727,87 +1731,6 @@ static void rcu_idle_count_callbacks_posted(void) __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); } -/* - * Data for flushing lazy RCU callbacks at OOM time. - */ -static atomic_t oom_callback_count; -static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); - -/* - * RCU OOM callback -- decrement the outstanding count and deliver the - * wake-up if we are the last one. - */ -static void rcu_oom_callback(struct rcu_head *rhp) -{ - if (atomic_dec_and_test(&oom_callback_count)) - wake_up(&oom_callback_wq); -} - -/* - * Post an rcu_oom_notify callback on the current CPU if it has at - * least one lazy callback. This will unnecessarily post callbacks - * to CPUs that already have a non-lazy callback at the end of their - * callback list, but this is an infrequent operation, so accept some - * extra overhead to keep things simple. - */ -static void rcu_oom_notify_cpu(void *unused) -{ - struct rcu_state *rsp; - struct rcu_data *rdp; - - for_each_rcu_flavor(rsp) { - rdp = raw_cpu_ptr(rsp->rda); - if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) { - atomic_inc(&oom_callback_count); - rsp->call(&rdp->oom_head, rcu_oom_callback); - } - } -} - -/* - * If low on memory, ensure that each CPU has a non-lazy callback. - * This will wake up CPUs that have only lazy callbacks, in turn - * ensuring that they free up the corresponding memory in a timely manner. - * Because an uncertain amount of memory will be freed in some uncertain - * timeframe, we do not claim to have freed anything. - */ -static int rcu_oom_notify(struct notifier_block *self, - unsigned long notused, void *nfreed) -{ - int cpu; - - /* Wait for callbacks from earlier instance to complete. */ - wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); - smp_mb(); /* Ensure callback reuse happens after callback invocation. */ - - /* - * Prevent premature wakeup: ensure that all increments happen - * before there is a chance of the counter reaching zero. - */ - atomic_set(&oom_callback_count, 1); - - for_each_online_cpu(cpu) { - smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); - cond_resched_tasks_rcu_qs(); - } - - /* Unconditionally decrement: no need to wake ourselves up. */ - atomic_dec(&oom_callback_count); - - return NOTIFY_OK; -} - -static struct notifier_block rcu_oom_nb = { - .notifier_call = rcu_oom_notify -}; - -static int __init rcu_register_oom_notifier(void) -{ - register_oom_notifier(&rcu_oom_nb); - return 0; -} -early_initcall(rcu_register_oom_notifier); - #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ #ifdef CONFIG_RCU_FAST_NO_HZ |