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| author | Michael S. Tsirkin <mst@redhat.com> | 2018-01-26 01:36:29 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2018-01-29 12:02:53 -0500 |
| commit | a259df36d1fbf25f0e4f649fdb84e4527e5640ed (patch) | |
| tree | a5a2c6d057c491dc2235cd443e1bf7a6823d74b2 /include/linux/ptr_ring.h | |
| parent | 8619d384eb5e9256a9d4ebe96c1832ac9b9049d6 (diff) | |
| download | lwn-a259df36d1fbf25f0e4f649fdb84e4527e5640ed.tar.gz lwn-a259df36d1fbf25f0e4f649fdb84e4527e5640ed.zip | |
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.h | 11 |
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: |