srcu: Provide polling interfaces for Tiny SRCU grace periods

There is a need for a polling interface for SRCU grace periods, so this commit supplies get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and poll_state_synchronize_srcu() for this purpose. The first can be used if future grace periods are inevitable (perhaps due to a later call_srcu() invocation), the second if future grace periods might not otherwise happen, and the third to check if a grace period has elapsed since the corresponding call to either of the first two. As with get_state_synchronize_rcu() and cond_synchronize_rcu(), the return value from either get_state_synchronize_srcu() or start_poll_synchronize_srcu() must be passed in to a later call to poll_state_synchronize_srcu().

Paul E. McKenney committed 6 years ago

Commit 8b5bd671 parent 29d2bb94 files · +59 −2Browse files

Unified · Split

4 files

include/linux/rcupdate.h +2 −0
include/linux/srcu.h +3 −0
include/linux/srcutiny.h +1 −0
kernel/rcu/srcutiny.c +53 −2

include/linux/rcupdate.h+2−0

@@ -33,6 +33,8 @@ · 32 unmodified lines
33	#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))	33	#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
34	#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))	34	#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
35	#define ulong2long(a) ((long )(&(a)))	35	#define ulong2long(a) ((long )(&(a)))
		36	#define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
		37	#define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
36		38
37	/* Exported common interfaces */	39	/* Exported common interfaces */
38	void call_rcu(struct rcu_head *head, rcu_callback_t func);	40	void call_rcu(struct rcu_head *head, rcu_callback_t func);

include/linux/srcu.h+3−0

@@ -60,6 +60,9 @@ void cleanup_srcu_struct(struct srcu_struct *ssp); · 59 unmodified lines
60	int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);	60	int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
61	void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);	61	void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
62	void synchronize_srcu(struct srcu_struct *ssp);	62	void synchronize_srcu(struct srcu_struct *ssp);
		63	unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
		64	unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
		65	bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
63		66
64	#ifdef CONFIG_DEBUG_LOCK_ALLOC	67	#ifdef CONFIG_DEBUG_LOCK_ALLOC
65		68

include/linux/srcutiny.h+1−0

@@ -16,6 +16,7 @@ · 15 unmodified lines
16	struct srcu_struct {	16	struct srcu_struct {
17	short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */	17	short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
18	unsigned short srcu_idx; /* Current reader array element in bit 0x2. */	18	unsigned short srcu_idx; /* Current reader array element in bit 0x2. */
		19	unsigned short srcu_idx_max; /* Furthest future srcu_idx request. */
19	u8 srcu_gp_running; /* GP workqueue running? */	20	u8 srcu_gp_running; /* GP workqueue running? */
20	u8 srcu_gp_waiting; /* GP waiting for readers? */	21	u8 srcu_gp_waiting; /* GP waiting for readers? */
21	struct swait_queue_head srcu_wq;	22	struct swait_queue_head srcu_wq;

kernel/rcu/srcutiny.c+53−2

@@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) · 33 unmodified lines
34	ssp->srcu_gp_running = false;	34	ssp->srcu_gp_running = false;
35	ssp->srcu_gp_waiting = false;	35	ssp->srcu_gp_waiting = false;
36	ssp->srcu_idx = 0;	36	ssp->srcu_idx = 0;
		37	ssp->srcu_idx_max = 0;
37	INIT_WORK(&ssp->srcu_work, srcu_drive_gp);	38	INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
38	INIT_LIST_HEAD(&ssp->srcu_work.entry);	39	INIT_LIST_HEAD(&ssp->srcu_work.entry);
39	return 0;	40	return 0;
@@ -84,6 +85,8 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) · 44 unmodified lines
84	WARN_ON(ssp->srcu_gp_waiting);	85	WARN_ON(ssp->srcu_gp_waiting);
85	WARN_ON(ssp->srcu_cb_head);	86	WARN_ON(ssp->srcu_cb_head);
86	WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);	87	WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
		88	WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
		89	WARN_ON(ssp->srcu_idx & 0x1);
87	}	90	}
88	EXPORT_SYMBOL_GPL(cleanup_srcu_struct);	91	EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
89		92
@@ -114,7 +117,7 @@ void srcu_drive_gp(struct work_struct *wp) · 24 unmodified lines
114	struct srcu_struct *ssp;	117	struct srcu_struct *ssp;
115		118
116	ssp = container_of(wp, struct srcu_struct, srcu_work);	119	ssp = container_of(wp, struct srcu_struct, srcu_work);
117	if (ssp->srcu_gp_running \|\| !READ_ONCE(ssp->srcu_cb_head))	120	if (ssp->srcu_gp_running \|\| USHORT_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
118	return; /* Already running or nothing to do. */	121	return; /* Already running or nothing to do. */
119		122
120	/* Remove recently arrived callbacks and wait for readers. */	123	/* Remove recently arrived callbacks and wait for readers. */
@@ -147,13 +150,19 @@ void srcu_drive_gp(struct work_struct *wp) · 26 unmodified lines
147	* straighten that out.	150	* straighten that out.
148	*/	151	*/
149	WRITE_ONCE(ssp->srcu_gp_running, false);	152	WRITE_ONCE(ssp->srcu_gp_running, false);
150	if (READ_ONCE(ssp->srcu_cb_head))	153	if (USHORT_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
151	schedule_work(&ssp->srcu_work);	154	schedule_work(&ssp->srcu_work);
152	}	155	}
153	EXPORT_SYMBOL_GPL(srcu_drive_gp);	156	EXPORT_SYMBOL_GPL(srcu_drive_gp);
154		157
155	static void srcu_gp_start_if_needed(struct srcu_struct *ssp)	158	static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
156	{	159	{
		160	unsigned short cookie;
		161
		162	cookie = get_state_synchronize_srcu(ssp);
		163	if (USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
		164	return;
		165	WRITE_ONCE(ssp->srcu_idx_max, cookie);
157	if (!READ_ONCE(ssp->srcu_gp_running)) {	166	if (!READ_ONCE(ssp->srcu_gp_running)) {
158	if (likely(srcu_init_done))	167	if (likely(srcu_init_done))
159	schedule_work(&ssp->srcu_work);	168	schedule_work(&ssp->srcu_work);
@@ -196,6 +205,48 @@ void synchronize_srcu(struct srcu_struct *ssp) · 36 unmodified lines
196	}	205	}
197	EXPORT_SYMBOL_GPL(synchronize_srcu);	206	EXPORT_SYMBOL_GPL(synchronize_srcu);
198		207
		208	/*
		209	* get_state_synchronize_srcu - Provide an end-of-grace-period cookie
		210	*/
		211	unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
		212	{
		213	unsigned long ret;
		214
		215	barrier();
		216	ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
		217	barrier();
		218	return ret & USHRT_MAX;
		219	}
		220	EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
		221
		222	/*
		223	* start_poll_synchronize_srcu - Provide cookie and start grace period
		224	*
		225	* The difference between this and get_state_synchronize_srcu() is that
		226	* this function ensures that the poll_state_synchronize_srcu() will
		227	* eventually return the value true.
		228	*/
		229	unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
		230	{
		231	unsigned long ret = get_state_synchronize_srcu(ssp);
		232
		233	srcu_gp_start_if_needed(ssp);
		234	return ret;
		235	}
		236	EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
		237
		238	/*
		239	* poll_state_synchronize_srcu - Has cookie's grace period ended?
		240	*/
		241	bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
		242	{
		243	bool ret = USHORT_CMP_GE(READ_ONCE(ssp->srcu_idx), cookie);
		244
		245	barrier();
		246	return ret;
		247	}
		248	EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
		249
199	/* Lockdep diagnostics. */	250	/* Lockdep diagnostics. */
200	void __init rcu_scheduler_starting(void)	251	void __init rcu_scheduler_starting(void)
201	{	252	{

srcu: Provide polling interfaces for Tiny SRCU grace periods

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