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
......@@ -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:
......
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