Make Tiny call_srcu() safe to call from unknown context: when interrupts are disabled and the scheduler is up, stage the callback on the srcu_struct's lockless list that an irq_work re-issues later. Tiny SRCU is uniprocessor, so there is no CPU-offline drain. Gated by CONFIG_RCU_DEFER, like Tree SRCU.
Suggested-by: Paul E. McKenney <[email protected]> Signed-off-by: Puranjay Mohan <[email protected]> --- include/linux/srcutiny.h | 11 ++++++--- kernel/rcu/srcutiny.c | 53 +++++++++++++++++++++++++++++++++++++--- 2 files changed, 56 insertions(+), 8 deletions(-) diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index fbcf13bc12d15..47275d182966c 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -12,6 +12,7 @@ #define _LINUX_SRCU_TINY_H #include <linux/irq_work_types.h> +#include <linux/llist.h> #include <linux/swait.h> struct srcu_struct { @@ -26,6 +27,8 @@ struct srcu_struct { struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */ struct work_struct srcu_work; /* For driving grace periods. */ struct irq_work srcu_irq_work; /* Defer schedule_work() to irq work. */ + struct llist_head defer_cbs; /* Callbacks deferred on re-entry. */ + struct irq_work defer_iw; /* Registers defer_cbs later. */ #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ @@ -33,6 +36,7 @@ struct srcu_struct { void srcu_drive_gp(struct work_struct *wp); void srcu_tiny_irq_work(struct irq_work *irq_work); +void srcu_defer_drain(struct irq_work *irq_work); #define __SRCU_STRUCT_INIT(name, __ignored, ___ignored, ____ignored) \ { \ @@ -40,6 +44,8 @@ void srcu_tiny_irq_work(struct irq_work *irq_work); .srcu_cb_tail = &name.srcu_cb_head, \ .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \ .srcu_irq_work = { .func = srcu_tiny_irq_work }, \ + .defer_cbs = LLIST_HEAD_INIT(name.defer_cbs), \ + .defer_iw = { .func = srcu_defer_drain }, \ __SRCU_DEP_MAP_INIT(name) \ } @@ -131,10 +137,7 @@ static inline void synchronize_srcu_expedited(struct srcu_struct *ssp) synchronize_srcu(ssp); } -static inline void srcu_barrier(struct srcu_struct *ssp) -{ - synchronize_srcu(ssp); -} +void srcu_barrier(struct srcu_struct *ssp); static inline void srcu_expedite_current(struct srcu_struct *ssp) { } #define srcu_check_read_flavor(ssp, read_flavor) do { } while (0) diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index f9c498ae75df2..b454d3e828edc 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -10,6 +10,7 @@ #include <linux/export.h> #include <linux/irq_work.h> +#include <linux/llist.h> #include <linux/mutex.h> #include <linux/preempt.h> #include <linux/rcupdate_wait.h> @@ -43,6 +44,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) INIT_WORK(&ssp->srcu_work, srcu_drive_gp); INIT_LIST_HEAD(&ssp->srcu_work.entry); init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work); + init_llist_head(&ssp->defer_cbs); + init_irq_work(&ssp->defer_iw, srcu_defer_drain); return 0; } @@ -215,11 +218,11 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp) } /* - * Enqueue an SRCU callback on the specified srcu_struct structure, - * initiating grace-period processing if it is not already running. + * Enqueue @rhp on the callback list. Also called by srcu_defer_drain() to + * re-issue a deferred callback, so it must not re-check the deferral condition. */ -void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, - rcu_callback_t func) +static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func) { unsigned long flags; @@ -233,6 +236,39 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, srcu_gp_start_if_needed(ssp); preempt_enable(); } + +void srcu_defer_drain(struct irq_work *iw) +{ + struct srcu_struct *ssp = container_of(iw, struct srcu_struct, defer_iw); + struct llist_node *node, *next; + + /* + * Callbacks have no mutual ordering guarantee and srcu_barrier() has + * already flushed us, so drain in llist order without reversing. + */ + llist_for_each_safe(node, next, llist_del_all(&ssp->defer_cbs)) { + struct rcu_head *rhp = (struct rcu_head *)node; + + srcu_do_enqueue(ssp, rhp, rhp->func); + } +} +EXPORT_SYMBOL_GPL(srcu_defer_drain); + +void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, + rcu_callback_t func) +{ + if (should_rcu_defer()) { + rhp->func = func; + if (llist_add((struct llist_node *)rhp, &ssp->defer_cbs)) + irq_work_queue(&ssp->defer_iw); + return; + } + + /* An NMI reaching here entered with irqs enabled, so the enqueue can race. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && in_nmi()); + + srcu_do_enqueue(ssp, rhp, func); +} EXPORT_SYMBOL_GPL(call_srcu); /* @@ -262,6 +298,15 @@ void synchronize_srcu(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/* Register any deferred callbacks, then wait for all in-flight ones. */ +void srcu_barrier(struct srcu_struct *ssp) +{ + if (IS_ENABLED(CONFIG_RCU_DEFER)) + irq_work_sync(&ssp->defer_iw); + synchronize_srcu(ssp); +} +EXPORT_SYMBOL_GPL(srcu_barrier); + /* * get_state_synchronize_srcu - Provide an end-of-grace-period cookie */ -- 2.53.0-Meta
