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ptr_ring: READ/WRITE_ONCE for __ptr_ring_empty

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Lockless __ptr_ring_empty requires that consumer head is read and
written at once, atomically. Annotate accordingly to make sure compiler
does it correctly.  Switch locked callers to __ptr_ring_peek which does
not support the lockless operation.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Michael S. Tsirkin 2018-01-26 01:36:29 +02:00 committed by David S. Miller
parent 8619d384eb
commit a259df36d1
1 changed files with 8 additions and 3 deletions
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11
include/linux/ptr_ring.h
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@ -196,7 +196,9 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r)
*/ */
static inline bool __ptr_ring_empty(struct ptr_ring *r) static inline bool __ptr_ring_empty(struct ptr_ring *r)
{ {
return !__ptr_ring_peek(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) static inline bool ptr_ring_empty(struct ptr_ring *r)
@ -285,7 +287,8 @@ static inline void __ptr_ring_discard_one(struct ptr_ring *r)
consumer_head = 0; consumer_head = 0;
r->consumer_tail = 0; r->consumer_tail = 0;
} }
r->consumer_head = consumer_head; /* 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) static inline void *__ptr_ring_consume(struct ptr_ring *r)
@ -541,7 +544,9 @@ static inline void ptr_ring_unconsume(struct ptr_ring *r, void **batch, int n,
goto done; goto done;
} }
r->queue[head] = batch[--n]; r->queue[head] = batch[--n];
r->consumer_tail = r->consumer_head = head; r->consumer_tail = head;
/* matching READ_ONCE in __ptr_ring_empty for lockless tests */
WRITE_ONCE(r->consumer_head, head);
} }
done: done: