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authorMichael S. Tsirkin <mst@redhat.com>2018-01-26 02:36:29 +0300
committerDavid S. Miller <davem@davemloft.net>2018-01-29 20:02:53 +0300
commita259df36d1fbf25f0e4f649fdb84e4527e5640ed (patch)
treea5a2c6d057c491dc2235cd443e1bf7a6823d74b2 /include/linux/ptr_ring.h
parent8619d384eb5e9256a9d4ebe96c1832ac9b9049d6 (diff)
downloadlinux-a259df36d1fbf25f0e4f649fdb84e4527e5640ed.tar.xz
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: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/ptr_ring.h')
-rw-r--r--include/linux/ptr_ring.h11
1 files changed, 8 insertions, 3 deletions
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 8594c7b37c15..9a72d8fec50e 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -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: