diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcu/srcu.c | 84 |
1 files changed, 46 insertions, 38 deletions
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c index 90ffea31b188..3cfcc59bddf3 100644 --- a/kernel/rcu/srcu.c +++ b/kernel/rcu/srcu.c @@ -43,6 +43,7 @@ static int init_srcu_struct_fields(struct srcu_struct *sp) { sp->completed = 0; sp->srcu_gp_seq = 0; + atomic_set(&sp->srcu_exp_cnt, 0); spin_lock_init(&sp->queue_lock); rcu_segcblist_init(&sp->srcu_cblist); INIT_DELAYED_WORK(&sp->work, process_srcu); @@ -179,7 +180,6 @@ static bool srcu_readers_active(struct srcu_struct *sp) return sum; } -#define SRCU_CALLBACK_BATCH 10 #define SRCU_INTERVAL 1 /** @@ -197,6 +197,7 @@ static bool srcu_readers_active(struct srcu_struct *sp) */ void cleanup_srcu_struct(struct srcu_struct *sp) { + WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt)); if (WARN_ON(srcu_readers_active(sp))) return; /* Leakage unless caller handles error. */ if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist))) @@ -244,13 +245,10 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); * We use an adaptive strategy for synchronize_srcu() and especially for * synchronize_srcu_expedited(). We spin for a fixed time period * (defined below) to allow SRCU readers to exit their read-side critical - * sections. If there are still some readers after 10 microseconds, - * we repeatedly block for 1-millisecond time periods. This approach - * has done well in testing, so there is no need for a config parameter. + * sections. If there are still some readers after a few microseconds, + * we repeatedly block for 1-millisecond time periods. */ #define SRCU_RETRY_CHECK_DELAY 5 -#define SYNCHRONIZE_SRCU_TRYCOUNT 2 -#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12 /* * Start an SRCU grace period. @@ -267,16 +265,16 @@ static void srcu_gp_start(struct srcu_struct *sp) } /* - * Wait until all readers counted by array index idx complete, but loop - * a maximum of trycount times. The caller must ensure that ->completed - * is not changed while checking. + * Wait until all readers counted by array index idx complete, but + * loop an additional time if there is an expedited grace period pending. + * The caller must ensure that ->completed is not changed while checking. */ static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount) { for (;;) { if (srcu_readers_active_idx_check(sp, idx)) return true; - if (--trycount <= 0) + if (--trycount + !!atomic_read(&sp->srcu_exp_cnt) <= 0) return false; udelay(SRCU_RETRY_CHECK_DELAY); } @@ -364,7 +362,7 @@ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay); /* * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). */ -static void __synchronize_srcu(struct srcu_struct *sp, int trycount) +static void __synchronize_srcu(struct srcu_struct *sp) { struct rcu_synchronize rcu; struct rcu_head *head = &rcu.head; @@ -401,6 +399,32 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount) } /** + * synchronize_srcu_expedited - Brute-force SRCU grace period + * @sp: srcu_struct with which to synchronize. + * + * Wait for an SRCU grace period to elapse, but be more aggressive about + * spinning rather than blocking when waiting. + * + * Note that synchronize_srcu_expedited() has the same deadlock and + * memory-ordering properties as does synchronize_srcu(). + */ +void synchronize_srcu_expedited(struct srcu_struct *sp) +{ + bool do_norm = rcu_gp_is_normal(); + + if (!do_norm) { + atomic_inc(&sp->srcu_exp_cnt); + smp_mb__after_atomic(); /* increment before GP. */ + } + __synchronize_srcu(sp); + if (!do_norm) { + smp_mb__before_atomic(); /* GP before decrement. */ + atomic_dec(&sp->srcu_exp_cnt); + } +} +EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); + +/** * synchronize_srcu - wait for prior SRCU read-side critical-section completion * @sp: srcu_struct with which to synchronize. * @@ -441,29 +465,14 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount) */ void synchronize_srcu(struct srcu_struct *sp) { - __synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal()) - ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT - : SYNCHRONIZE_SRCU_TRYCOUNT); + if (rcu_gp_is_expedited()) + synchronize_srcu_expedited(sp); + else + __synchronize_srcu(sp); } EXPORT_SYMBOL_GPL(synchronize_srcu); /** - * synchronize_srcu_expedited - Brute-force SRCU grace period - * @sp: srcu_struct with which to synchronize. - * - * Wait for an SRCU grace period to elapse, but be more aggressive about - * spinning rather than blocking when waiting. - * - * Note that synchronize_srcu_expedited() has the same deadlock and - * memory-ordering properties as does synchronize_srcu(). - */ -void synchronize_srcu_expedited(struct srcu_struct *sp) -{ - __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT); -} -EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); - -/** * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete. * @sp: srcu_struct on which to wait for in-flight callbacks. */ @@ -490,7 +499,7 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed); * Core SRCU state machine. Advance callbacks from ->batch_check0 to * ->batch_check1 and then to ->batch_done as readers drain. */ -static void srcu_advance_batches(struct srcu_struct *sp, int trycount) +static void srcu_advance_batches(struct srcu_struct *sp) { int idx; @@ -521,8 +530,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount) if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) { idx = 1 ^ (sp->completed & 1); - if (!try_check_zero(sp, idx, trycount)) - return; /* readers present, retry after SRCU_INTERVAL */ + if (!try_check_zero(sp, idx, 1)) + return; /* readers present, retry later. */ srcu_flip(sp); rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2); } @@ -534,9 +543,8 @@ static void srcu_advance_batches(struct srcu_struct *sp, int trycount) * so check at least twice in quick succession after a flip. */ idx = 1 ^ (sp->completed & 1); - trycount = trycount < 2 ? 2 : trycount; - if (!try_check_zero(sp, idx, trycount)) - return; /* readers present, retry after SRCU_INTERVAL */ + if (!try_check_zero(sp, idx, 2)) + return; /* readers present, retry after later. */ srcu_gp_end(sp); } } @@ -602,8 +610,8 @@ void process_srcu(struct work_struct *work) sp = container_of(work, struct srcu_struct, work.work); - srcu_advance_batches(sp, 1); + srcu_advance_batches(sp); srcu_invoke_callbacks(sp); - srcu_reschedule(sp, SRCU_INTERVAL); + srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); } EXPORT_SYMBOL_GPL(process_srcu); |