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// SPDX-License-Identifier: GPL-2.0+
/*
* RCU segmented callback lists, function definitions
*
* Copyright IBM Corporation, 2017
*
* Authors: Paul E. McKenney <paulmck@linux.ibm.com>
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/rcupdate.h>
#include "rcu_segcblist.h"
/* Initialize simple callback list. */
void rcu_cblist_init(struct rcu_cblist *rclp)
{
rclp->head = NULL;
rclp->tail = &rclp->head;
rclp->len = 0;
rclp->len_lazy = 0;
}
/*
* Enqueue an rcu_head structure onto the specified callback list.
* This function assumes that the callback is non-lazy because it
* is intended for use by no-CBs CPUs, which do not distinguish
* between lazy and non-lazy RCU callbacks.
*/
void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp)
{
*rclp->tail = rhp;
rclp->tail = &rhp->next;
WRITE_ONCE(rclp->len, rclp->len + 1);
}
/*
* Flush the second rcu_cblist structure onto the first one, obliterating
* any contents of the first. If rhp is non-NULL, enqueue it as the sole
* element of the second rcu_cblist structure, but ensuring that the second
* rcu_cblist structure, if initially non-empty, always appears non-empty
* throughout the process. If rdp is NULL, the second rcu_cblist structure
* is instead initialized to empty.
*/
void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
struct rcu_cblist *srclp,
struct rcu_head *rhp)
{
drclp->head = srclp->head;
if (drclp->head)
drclp->tail = srclp->tail;
else
drclp->tail = &drclp->head;
drclp->len = srclp->len;
drclp->len_lazy = srclp->len_lazy;
if (!rhp) {
rcu_cblist_init(srclp);
} else {
rhp->next = NULL;
srclp->head = rhp;
srclp->tail = &rhp->next;
WRITE_ONCE(srclp->len, 1);
srclp->len_lazy = 0;
}
}
/*
* Dequeue the oldest rcu_head structure from the specified callback
* list. This function assumes that the callback is non-lazy, but
* the caller can later invoke rcu_cblist_dequeued_lazy() if it
* finds otherwise (and if it cares about laziness). This allows
* different users to have different ways of determining laziness.
*/
struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
{
struct rcu_head *rhp;
rhp = rclp->head;
if (!rhp)
return NULL;
rclp->len--;
rclp->head = rhp->next;
if (!rclp->head)
rclp->tail = &rclp->head;
return rhp;
}
/* Set the length of an rcu_segcblist structure. */
void rcu_segcblist_set_len(struct rcu_segcblist *rsclp, long v)
{
#ifdef CONFIG_RCU_NOCB_CPU
atomic_long_set(&rsclp->len, v);
#else
WRITE_ONCE(rsclp->len, v);
#endif
}
/*
* Increase the numeric length of an rcu_segcblist structure by the
* specified amount, which can be negative. This can cause the ->len
* field to disagree with the actual number of callbacks on the structure.
* This increase is fully ordered with respect to the callers accesses
* both before and after.
*/
void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v)
{
#ifdef CONFIG_RCU_NOCB_CPU
smp_mb__before_atomic(); /* Up to the caller! */
atomic_long_add(v, &rsclp->len);
smp_mb__after_atomic(); /* Up to the caller! */
#else
smp_mb(); /* Up to the caller! */
WRITE_ONCE(rsclp->len, rsclp->len + v);
smp_mb(); /* Up to the caller! */
#endif
}
/*
* Increase the numeric length of an rcu_segcblist structure by one.
* This can cause the ->len field to disagree with the actual number of
* callbacks on the structure. This increase is fully ordered with respect
* to the callers accesses both before and after.
*/
void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp)
{
rcu_segcblist_add_len(rsclp, 1);
}
/*
* Exchange the numeric length of the specified rcu_segcblist structure
* with the specified value. This can cause the ->len field to disagree
* with the actual number of callbacks on the structure. This exchange is
* fully ordered with respect to the callers accesses both before and after.
*/
long rcu_segcblist_xchg_len(struct rcu_segcblist *rsclp, long v)
{
#ifdef CONFIG_RCU_NOCB_CPU
return atomic_long_xchg(&rsclp->len, v);
#else
long ret = rsclp->len;
smp_mb(); /* Up to the caller! */
WRITE_ONCE(rsclp->len, v);
smp_mb(); /* Up to the caller! */
return ret;
#endif
}
/*
* Initialize an rcu_segcblist structure.
*/
void rcu_segcblist_init(struct rcu_segcblist *rsclp)
{
int i;
BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq));
BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq));
rsclp->head = NULL;
for (i = 0; i < RCU_CBLIST_NSEGS; i++)
rsclp->tails[i] = &rsclp->head;
rcu_segcblist_set_len(rsclp, 0);
rsclp->len_lazy = 0;
rsclp->enabled = 1;
}
/*
* Disable the specified rcu_segcblist structure, so that callbacks can
* no longer be posted to it. This structure must be empty.
*/
void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
{
WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
rsclp->enabled = 0;
}
/*
* Mark the specified rcu_segcblist structure as offloaded. This
* structure must be empty.
*/
void rcu_segcblist_offload(struct rcu_segcblist *rsclp)
{
rsclp->offloaded = 1;
}
/*
* Does the specified rcu_segcblist structure contain callbacks that
* are ready to be invoked?
*/
bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp)
{
return rcu_segcblist_is_enabled(rsclp) &&
&rsclp->head != rsclp->tails[RCU_DONE_TAIL];
}
/*
* Does the specified rcu_segcblist structure contain callbacks that
* are still pending, that is, not yet ready to be invoked?
*/
bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp)
{
return rcu_segcblist_is_enabled(rsclp) &&
!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL);
}
/*
* Return a pointer to the first callback in the specified rcu_segcblist
* structure. This is useful for diagnostics.
*/
struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp)
{
if (rcu_segcblist_is_enabled(rsclp))
return rsclp->head;
return NULL;
}
/*
* Return a pointer to the first pending callback in the specified
* rcu_segcblist structure. This is useful just after posting a given
* callback -- if that callback is the first pending callback, then
* you cannot rely on someone else having already started up the required
* grace period.
*/
struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp)
{
if (rcu_segcblist_is_enabled(rsclp))
return *rsclp->tails[RCU_DONE_TAIL];
return NULL;
}
/*
* Return false if there are no CBs awaiting grace periods, otherwise,
* return true and store the nearest waited-upon grace period into *lp.
*/
bool rcu_segcblist_nextgp(struct rcu_segcblist *rsclp, unsigned long *lp)
{
if (!rcu_segcblist_pend_cbs(rsclp))
return false;
*lp = rsclp->gp_seq[RCU_WAIT_TAIL];
return true;
}
/*
* Enqueue the specified callback onto the specified rcu_segcblist
* structure, updating accounting as needed. Note that the ->len
* field may be accessed locklessly, hence the WRITE_ONCE().
* The ->len field is used by rcu_barrier() and friends to determine
* if it must post a callback on this structure, and it is OK
* for rcu_barrier() to sometimes post callbacks needlessly, but
* absolutely not OK for it to ever miss posting a callback.
*/
void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy)
{
rcu_segcblist_inc_len(rsclp);
if (lazy)
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is enqueued. */
rhp->next = NULL;
WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp);
WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], &rhp->next);
}
/*
* Entrain the specified callback onto the specified rcu_segcblist at
* the end of the last non-empty segment. If the entire rcu_segcblist
* is empty, make no change, but return false.
*
* This is intended for use by rcu_barrier()-like primitives, -not-
* for normal grace-period use. IMPORTANT: The callback you enqueue
* will wait for all prior callbacks, NOT necessarily for a grace
* period. You have been warned.
*/
bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy)
{
int i;
if (rcu_segcblist_n_cbs(rsclp) == 0)
return false;
rcu_segcblist_inc_len(rsclp);
if (lazy)
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is entrained. */
rhp->next = NULL;
for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
if (rsclp->tails[i] != rsclp->tails[i - 1])
break;
WRITE_ONCE(*rsclp->tails[i],
|