include/linux/srcutree.h

1 /* SPDX-License-Identifier: GPL-2.0+ */
3  * Sleepable Read-Copy Update mechanism for mutual exclusion,
22 	atomic_long_t srcu_locks;	/* Locks per CPU. */
23 	atomic_long_t srcu_unlocks;	/* Unlocks per CPU. */
27  * Per-CPU structure feeding into leaf srcu_node, similar in function
31 	/* Read-side state. */
32 	struct srcu_ctr srcu_ctrs[2];		/* Locks and unlocks per CPU. */
36 	/* Update-side state. */
47 						/*  ->srcu_data_have_cbs[]. */
48 	int cpu;  member
58 						/*  if greater than ->srcu_gp_seq. */
62 	int grplo;				/* Least CPU for node. */
63 	int grphi;				/* Biggest CPU for node. */
67  * Per-SRCU-domain structure, update-side data linked from srcu_struct.
73 	int srcu_size_state;			/* Small-to-big transition state. */
77 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
82 	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
84 	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
85 	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
100  * Per-SRCU-domain structure, similar in function to rcu_state.
104 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
106 	struct srcu_usage *srcu_sup;		/* Update-side data. */
109 // Values for size state variable (->srcu_size_state).  Once the state
110 // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
114 #define SRCU_SIZE_SMALL		0	// No srcu_node combining tree, ->node == NULL
116 					//  and then referenced by ->node.  It will not be used.
123 					//  invocations that were running on a non-boot CPU
124 					//  and using the boot CPU's callback queue will have
126 #define SRCU_SIZE_WAIT_CBS1	4	// Don't trust the ->srcu_have_cbs[] grace-period
127 #define SRCU_SIZE_WAIT_CBS2	5	//  sequence elements or the ->srcu_data_have_cbs[]
128 #define SRCU_SIZE_WAIT_CBS3	6	//  CPU-bitmask elements until all four elements of
133 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
146 #define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
147 #define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)
176  * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
179  * files, the per-CPU variable rules nevertheless require that the
191  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
215 // Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that
219 	return scpp - &ssp->sda->srcu_ctrs[0];  in __srcu_ptr_to_ctr()
222 // Converts an integer to a per-CPU pointer to the corresponding
223 // ->srcu_ctrs[] array element.
226 	return &ssp->sda->srcu_ctrs[idx];  in __srcu_ctr_to_ptr()
230  * Counts the new reader in the appropriate per-CPU element of the
234  * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side
236  * are a single instruction, or because they are a read-modify-write atomic
240  * on architectures that support NMIs but do not supply NMI-safe
245 	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);  in __srcu_read_lock_fast()
249 		this_cpu_inc(scp->srcu_locks.counter); /* Y */  in __srcu_read_lock_fast()
251 		atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks));  /* Z */  in __srcu_read_lock_fast()
258  * per-CPU element of the srcu_struct.  Note that this may well be a
259  * different CPU than that which was incremented by the corresponding
262  * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side
264  * are a single instruction, or because they are a read-modify-write atomic
268  * on architectures that support NMIs but do not supply NMI-safe
275 		this_cpu_inc(scp->srcu_unlocks.counter);  /* Z */  in __srcu_read_unlock_fast()
277 		atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks));  /* Z */  in __srcu_read_unlock_fast()
282  * Counts the new reader in the appropriate per-CPU element of the
286  * Note that this_cpu_inc() is an RCU read-side critical section either
288  * or because it is a read-modify-write atomic operation, depending on
293 	struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);  in __srcu_read_lock_lite()
296 	this_cpu_inc(scp->srcu_locks.counter); /* Y */  in __srcu_read_lock_lite()
303  * per-CPU element of the srcu_struct.  Note that this may well be a
304  * different CPU than that which was incremented by the corresponding
307  * Note that this_cpu_inc() is an RCU read-side critical section either
309  * or because it is a read-modify-write atomic operation, depending on
315 	this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter);  /* Z */  in __srcu_read_unlock_lite()
322 // needed only for flavors that require grace-period smp_mb() calls to be
326 	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);  in srcu_check_read_flavor_force()
328 	if (likely(READ_ONCE(sdp->srcu_reader_flavor) & read_flavor))  in srcu_check_read_flavor_force()
335 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels.