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Commit a259df36 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
Browse files

ptr_ring: READ/WRITE_ONCE for __ptr_ring_empty 



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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8619d384

include/linux/ptr_ring.h

+8 −3
Original line number Diff line number Diff line
@@ -196,7 +196,9 @@ static inline void *__ptr_ring_peek(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)
@@ -285,7 +287,8 @@ static inline void __ptr_ring_discard_one(struct ptr_ring *r) 
		consumer_head = 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)
@@ -541,7 +544,9 @@ static inline void ptr_ring_unconsume(struct ptr_ring *r, void **batch, int n, 
			goto done;

		}

		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: