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/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Definitions for the 'struct ptr_ring' datastructure.
*
* Author:
* Michael S. Tsirkin <[email protected]>
*
* Copyright (C) 2016 Red Hat, Inc.
*
* This is a limited-size FIFO maintaining pointers in FIFO order, with
* one CPU producing entries and another consuming entries from a FIFO.
*
* This implementation tries to minimize cache-contention when there is a
* single producer and a single consumer CPU.
*/
#ifndef _LINUX_PTR_RING_H
#define _LINUX_PTR_RING_H 1
#ifdef __KERNEL__
#include <linux/spinlock.h>
#include <linux/cache.h>
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <asm/errno.h>
#endif
struct ptr_ring {
int producer ____cacheline_aligned_in_smp;
spinlock_t producer_lock;
int consumer_head ____cacheline_aligned_in_smp; /* next valid entry */
int consumer_tail; /* next entry to invalidate */
spinlock_t consumer_lock;
/* Shared consumer/producer data */
/* Read-only by both the producer and the consumer */
int size ____cacheline_aligned_in_smp; /* max entries in queue */
int batch; /* number of entries to consume in a batch */
void **queue;
};
/* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax().
*
* NB: this is unlike __ptr_ring_empty in that callers must hold producer_lock:
* see e.g. ptr_ring_full.
*/
static inline bool __ptr_ring_full(struct ptr_ring *r)
{
return r->queue[r->producer];
}
static inline bool ptr_ring_full(struct ptr_ring *r)
{
bool ret;
spin_lock(&r->producer_lock);
ret = __ptr_ring_full(r);
spin_unlock(&r->producer_lock);
return ret;
}
static inline bool ptr_ring_full_irq(struct ptr_ring *r)
{
bool ret;
spin_lock_irq(&r->producer_lock);
ret = __ptr_ring_full(r);
spin_unlock_irq(&r->producer_lock);
return ret;
}
static inline bool ptr_ring_full_any(struct ptr_ring *r)
{
unsigned long flags;
bool ret;
spin_lock_irqsave(&r->producer_lock, flags);
ret = __ptr_ring_full(r);
spin_unlock_irqrestore(&r->producer_lock, flags);
return ret;
}
static inline bool ptr_ring_full_bh(struct ptr_ring *r)
{
bool ret;
spin_lock_bh(&r->producer_lock);
ret = __ptr_ring_full(r);
spin_unlock_bh(&r->producer_lock);
return ret;
}
/* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax(). Callers must hold producer_lock.
* Callers are responsible for making sure pointer that is being queued
* points to a valid data.
*/
static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
{
if (unlikely(!r->size) || r->queue[r->producer])
return -ENOSPC;
/* Make sure the pointer we are storing points to a valid data. */
/* Pairs with the dependency ordering in __ptr_ring_consume. */
smp_wmb();
WRITE_ONCE(r->queue[r->producer++], ptr);
if (unlikely(r->producer >= r->size))
r->producer = 0;
return 0;
}
/*
* Note: resize (below) nests producer lock within consumer lock, so if you
* consume in interrupt or BH context, you must disable interrupts/BH when
* calling this.
*/
static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
{
int ret;
spin_lock(&r->producer_lock);
ret = __ptr_ring_produce(r, ptr);
spin_unlock(&r->producer_lock);
return ret;
}
static inline int ptr_ring_produce_irq(struct ptr_ring *r, void *ptr)
{
int ret;
spin_lock_irq(&r->producer_lock);
ret = __ptr_ring_produce(r, ptr);
spin_unlock_irq(&r->producer_lock);
return ret;
}
static inline int ptr_ring_produce_any(struct ptr_ring *r, void *ptr)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&r->producer_lock, flags);
ret = __ptr_ring_produce(r, ptr);
spin_unlock_irqrestore(&r->producer_lock, flags);
return ret;
}
static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr)
{
int ret;
spin_lock_bh(&r->producer_lock);
ret = __ptr_ring_produce(r, ptr);
spin_unlock_bh(&r->producer_lock);
return ret;
}
static inline void *__ptr_ring_peek(struct ptr_ring *r)
{
if (likely(r->size))
return READ_ONCE(r->queue[r->consumer_head]);
return NULL;
}
/*
* Test ring empty status without taking any locks.
*
* NB: This is only safe to call if ring is never resized.
*
* However, if some other CPU consumes ring entries at the same time, the value
* returned is not guaranteed to be correct.
*
* In this case - to avoid incorrectly detecting the ring
* as empty - the CPU consuming the ring entries is responsible
* for either consuming all ring entries until the ring is empty,
* or synchronizing with some other CPU and causing it to
* re-test __ptr_ring_empty and/or consume the ring enteries
* after the synchronization point.
*
* Note: callers invoking this in a loop must use a compiler barrier,
* for example cpu_relax().
*/
static inline bool __ptr_ring_empty(struct ptr_ring *r)
{
if (likely(r->size))
return !r->queue[READ_ONCE(r->consumer_head)];
return true;
}
static inline bool ptr_ring_empty(struct ptr_ring *r)
{
bool ret;
spin_lock(&r->consumer_lock);
ret = __ptr_ring_empty(r);
spin_unlock(&r->consumer_lock);
return ret;
}
static inline bool ptr_ring_empty_irq(struct ptr_ring *r)
{
bool ret;
spin_lock_irq(&r->consumer_lock);
ret = __ptr_ring_empty(r);
spin_unlock_irq(&r->consumer_lock);
return ret;
}
static inline bool ptr_ring_empty_any(struct ptr_ring *r)
{
unsigned long flags;
bool ret;
spin_lock_irqsave(&r->consumer_lock, flags);
ret = __ptr_ring_empty(r);
spin_unlock_irqrestore(&r->consumer_lock, flags);
return ret;
}
static inline bool ptr_ring_empty_bh(struct ptr_ring *r)
{
bool ret;
spin_lock_bh(&r->consumer_lock);
ret = __ptr_ring_empty(r);
spin_unlock_bh(&r->consumer_lock);
return ret;
}
/* Must only be called after __ptr_ring_peek returned !NULL */
static inline void __ptr_ring_discard_one(struct ptr_ring *r)
{
/* Fundamentally, what we want to do is update consumer
* index and zero out the entry so producer can reuse it.
* Doing it naively at each consume would be as simple as:
* consumer = r->consumer;
* r->queue[consumer++] = NULL;
* if (unlikely(consumer >= r->size))
* consumer = 0;
* r->consumer = consumer;
* but that is suboptimal when the ring is full as producer is writing
* out new entries in the same cache line. Defer these updates until a
* batch of entries has been consumed.
*/
/* Note: we must keep consumer_head valid at all times for __ptr_ring_empty
* to work correctly.
*/
int consumer_head = r->consumer_head;
int head = consumer_head++;
/* Once we have processed enough entries invalidate them in
* the ring all at once so producer can reuse their space in the ring.
* We also do this when we reach end of the ring - not mandatory
* but helps keep the implementation simple.
*/
if (unlikely(consumer_head - r->consumer_tail >= r->batch ||
consumer_head >= r->size)) {
/* Zero out entries in the reverse order: this way we touch the
* cache line that producer might currently be reading the last;
* producer won't make progress and touch other cache lines
* besides the first one until we write out all entries.
*/
while (likely(head >= r->consumer_tail))
r->queue[head--] = NULL;
r->consumer_tail = consumer_head;
}
if (unlikely(consumer_head >= r->size)) {
consumer_head = 0;
r->consumer_tail = 0;
}
/* matching READ_ONCE in __ptr_ring_empty for lockless tests */
WRITE_ONCE(r->consumer_head, consumer_head);
}
static inline void *__ptr_ring_consume(struct ptr_ring *r)
{
void *ptr;
/* The READ_ONCE in __ptr_ring_peek guarantees that anyone
* accessing data through the pointer is up to date. Pairs
* with smp_wmb in __ptr_ring_produce.
*/
ptr = __ptr_ring_peek(r);
if (ptr)
__ptr_ring_discard_one(r);
return ptr;
}
static inline int __ptr_ring_consume_batched(struct ptr_ring *r,
void **array, int n)
{
void *ptr;
int i;
for (i = 0; i < n; i++) {
ptr = __ptr_ring_consume(r);
if (!ptr)
break;
array[i] = ptr;
}
return i;
}
/*
* Note: resize (below) nests producer lock within consumer lock, so if you
* call this in interrupt or BH context, you must disable interrupts/BH when
* producing.
*/
static inline void *ptr_ring_consume(struct ptr_ring *r)
{
void *ptr;
spin_lock(&r->consumer_lock);
ptr = __ptr_ring_consume(r);
spin_unlock(&r->consumer_lock);
return ptr;
}
static inline void *ptr_ring_consume_irq(struct ptr_ring *r)
{
void *ptr;
spin_lock_irq(&r->consumer_lock);
ptr = __ptr_ring_consume(r);
spin_unlock_irq(&r->consumer_lock);
return ptr;
}
static inline void *ptr_ring_consume_any(struct ptr_ring *r)
{
unsigned long flags;
void *ptr;
spin_lock_irqsave(&r->consumer_lock, flags);
ptr = __ptr_ring_consume(r);
spin_unlock_irqrestore(&r->consumer_lock, flags);
return ptr;
}
static inline void *ptr_ring_consume_bh(struct ptr_ring *r)
{
void *ptr;
spin_lock_bh(&r->consumer_lock);
ptr = __ptr_ring_consume(r);
spin_unlock_bh(&r->consumer_lock);
return ptr;
}
static inline int ptr_ring_consume_batched(struct ptr_ring *r,
void **array, int n)
{
int ret;
spin_lock(&r->consumer_lock);
ret = __ptr_ring_consume_batched(r, array, n);
spin_unlock(&r->consumer_lock);
return ret;
}
static inline int ptr_ring_consume_batched_irq(struct ptr_ring *r,
void **array, int n)
{
int ret;
spin_lock_irq(&r->consumer_lock);
ret = __ptr_ring_consume_batched(r, array, n);
spin_unlock_irq(&r->consumer_lock);
return ret;
}
static inline int ptr_ring_consume_batched_any(struct ptr_ring *r,
void **array, int n)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&r->consumer_lock, flags);
ret = __ptr_ring_consume_batched(r, array, n);
spin_unlock_irqrestore(&r->consumer_lock, flags);
return ret;
}
static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
void **array, int n)
{
int ret;
spin_lock_bh(&r->consumer_lock);
ret = __ptr_ring_consume_batched(r, array, n);
spin_unlock_bh(&r->consumer_lock);
return ret;
}
/* Cast to structure type and call a function without discarding from FIFO.
* Function must return a value.
* Callers must take consumer_lock.
*/
#define __PTR_RING_PEEK_CALL(r, f) ((f)(__ptr_ring_peek(r)))
#define PTR_RING_PEEK_CALL(r, f) ({ \
typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \
\
spin_lock(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \
spin_unlock(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v; \
})
#define PTR_RING_PEEK_CALL_IRQ(r, f) ({ \
typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \
\
spin_lock_irq(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \
spin_unlock_irq(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v; \
})
#define PTR_RING_PEEK_CALL_BH(r, f) ({ \
typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \
\
spin_lock_bh(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \
spin_unlock_bh(&(r)->consumer_lock); \
__PTR_RING_PEEK_CALL_v; \
})
#define PTR_RING_PEEK_CALL_ANY(r, f) ({ \
typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \
unsigned long __PTR_RING_PEEK_CALL_f;\
\
spin_lock_irqsave(&(r)->consumer_lock, __PTR_RING_PEEK_CALL_f); \
__PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \
spin_unlock_irqrestore(&(r)->consumer_lock, __PTR_RING_PEEK_CALL_f); \
__PTR_RING_PEEK_CALL_v; \
})
/* Not all gfp_t flags (besides GFP_KERNEL) are allowed. See
* documentation for vmalloc for which of them are legal.
*/
static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
{
if (size > KMALLOC_MAX_SIZE / sizeof(void *))
return NULL;
return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
}
static inline void __ptr_ring_set_size(struct ptr_ring *r, int size)
{
r->size = size;
r->batch = SMP_CACHE_BYTES * 2 / sizeof(*(r->queue));
/* We need to set batch at least to 1 to make logic
* in __ptr_ring_discard_one work correctly.
* Batching too much (because ring is small) would cause a lot of
* burstiness. Needs tuning, for now disable batching.
*/
if (r->batch > r->size / 2 || !r->batch)
r->batch = 1;
}
static inline int ptr_ring_init(struct ptr_ring *r, int size, gfp_t gfp)
{
r->queue = __ptr_ring_init_queue_alloc(size, gfp);
if (!r->queue)
return -ENOMEM;
__ptr_ring_set_size(r, size);
r->producer = r->consumer_head = r->consumer_tail = 0;
spin_lock_init(&r->producer_lock);
spin_lock_init(&r->consumer_lock);
return 0;
}
/*
* Return entries into ring. Destroy entries that don't fit.
*
* Note: this is expected to be a rare slow path operation.
*
* Note: producer lock is nested within consumer lock, so if you
* resize you must make sure all uses nest correctly.
* In particular if you consume ring in interrupt or BH context, you must
* disable interrupts/BH when doing so.
*/
static inline void ptr_ring_unconsume(struct ptr_ring *r, void **batch, int n,
void (*destroy)(void *))
{
unsigned long flags;
int head;
spin_lock_irqsave(&r->consumer_lock, flags);
spin_lock(&r->producer_lock);
if (!r->size)
goto done;
/*
* Clean out buffered entries (for simplicity). This way following code
* can test entries for NULL and if not assume they are valid.
*/
head = r->consumer_head - 1;
while (likely(head >= r->consumer_tail))
r->queue[head--] = NULL;
r->consumer_tail = r->consumer_head;
/*
* Go over entries in batch, start moving head back and copy entries.
* Stop when we run into previously unconsumed entries.
*/
while (n) {
head = r->consumer_head - 1;
if (head < 0)
head = r->size - 1;
if (r->queue[head]) {
/* This batch entry will have to be destroyed. */
goto done;
}
r->queue[head] = batch[--n];
r->consumer_tail = head;
/* matching READ_ONCE in __ptr_ring_empty for lockless tests */
WRITE_ONCE(r->consumer_head, head);
}
done:
/* Destroy all entries left in the batch. */
while (n)
destroy(batch[--n]);
spin_unlock(&r->producer_lock);
spin_unlock_irqrestore(&r->consumer_lock, flags);
}
static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
int size, gfp_t gfp,
void (*destroy)(void *))
{
int producer = 0;
void **old;
void *ptr;
while ((ptr = __ptr_ring_consume(r)))
if (producer < size)
queue[producer++] = ptr;
else if (destroy)
destroy(ptr);
if (producer >= size)
producer = 0;
__ptr_ring_set_size(r, size);
r->producer = producer;
r->consumer_head = 0;
r->consumer_tail = 0;
old = r->queue;
r->queue = queue;
return old;
}
/*
* Note: producer lock is nested within consumer lock, so if you
* resize you must make sure all uses nest correctly.
* In particular if you consume ring in interrupt or BH context, you must
* disable interrupts/BH when doing so.
*/
static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
void (*destroy)(void *))
{
unsigned long flags;
void **queue = __ptr_ring_init_queue_alloc(size, gfp);
void **old;
if (!queue)
return -ENOMEM;
spin_lock_irqsave(&(r)->consumer_lock, flags);
spin_lock(&(r)->producer_lock);
old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy);
spin_unlock(&(r)->producer_lock);
spin_unlock_irqrestore(&(r)->consumer_lock, flags);
kvfree(old);
return 0;
}
/*
* Note: producer lock is nested within consumer lock, so if you
* resize you must make sure all uses nest correctly.
* In particular if you consume ring in interrupt or BH context, you must
* disable interrupts/BH when doing so.
*/
static inline int ptr_ring_resize_multiple(struct ptr_ring **rings,
unsigned int nrings,
int size,
gfp_t gfp, void (*destroy)(void *))
{
unsigned long flags;
void ***queues;
int i;
queues = kmalloc_array(nrings, sizeof(*queues), gfp);
if (!queues)
goto noqueues;
for (i = 0; i < nrings; ++i) {
queues[i] = __ptr_ring_init_queue_alloc(size, gfp);
if (!queues[i])
goto nomem;
}
for (i = 0; i < nrings; ++i) {
spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
spin_lock(&(rings[i])->producer_lock);
queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
size, gfp, destroy);
spin_unlock(&(rings[i])->producer_lock);
spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags);
}
for (i = 0; i < nrings; ++i)
kvfree(queues[i]);
kfree(queues);
return 0;
nomem:
while (--i >= 0)
kvfree(queues[i]);
kfree(queues);
noqueues:
return -ENOMEM;
}
static inline void ptr_ring_cleanup(struct ptr_ring *r, void (*destroy)(void *))
{
void *ptr;
if (destroy)
while ((ptr = ptr_ring_consume(r)))
destroy(ptr);
kvfree(r->queue);
}
#endif /* _LINUX_PTR_RING_H */
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