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srcu: faster gp seq wrap-around
Using a higher value for the initial gp sequence counters allows for wrapping to occur faster. It can help with surfacing any issues that may be happening as a result of the wrap around. Signed-off-by: JP Kobryn <inwardvessel@gmail.com> Tested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
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@ -34,6 +34,9 @@
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#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
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#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
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#define RCU_SEQ_CTR_SHIFT 2
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#define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1)
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/* Exported common interfaces */
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void call_rcu(struct rcu_head *head, rcu_callback_t func);
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void rcu_barrier_tasks(void);
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@ -129,10 +129,23 @@ struct srcu_struct {
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#define SRCU_STATE_SCAN1 1
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#define SRCU_STATE_SCAN2 2
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/*
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* Values for initializing gp sequence fields. Higher values allow wrap arounds to
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* occur earlier.
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* The second value with state is useful in the case of static initialization of
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* srcu_usage where srcu_gp_seq_needed is expected to have some state value in its
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* lower bits (or else it will appear to be already initialized within
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* the call check_init_srcu_struct()).
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*/
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#define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
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#define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)
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#define __SRCU_USAGE_INIT(name) \
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{ \
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.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
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.srcu_gp_seq_needed = -1UL, \
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.srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \
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.srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \
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.srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \
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.work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \
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}
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@ -54,9 +54,6 @@
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* grace-period sequence number.
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*/
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#define RCU_SEQ_CTR_SHIFT 2
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#define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1)
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/* Low-order bit definition for polled grace-period APIs. */
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#define RCU_GET_STATE_COMPLETED 0x1
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@ -247,7 +247,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
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mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
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mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
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ssp->srcu_idx = 0;
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ssp->srcu_sup->srcu_gp_seq = 0;
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ssp->srcu_sup->srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL;
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ssp->srcu_sup->srcu_barrier_seq = 0;
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mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
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atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
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@ -258,7 +258,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
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if (!ssp->sda)
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goto err_free_sup;
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init_srcu_struct_data(ssp);
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ssp->srcu_sup->srcu_gp_seq_needed_exp = 0;
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ssp->srcu_sup->srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL;
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ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
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if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
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if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
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@ -266,7 +266,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
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WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
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}
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ssp->srcu_sup->srcu_ssp = ssp;
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smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */
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smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed,
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SRCU_GP_SEQ_INITIAL_VAL); /* Init done. */
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return 0;
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err_free_sda:
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