From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Fri, 26 Jan 2018 01:36:29 +0200
Subject: ptr_ring: READ/WRITE_ONCE for __ptr_ring_empty
Patch-mainline: v4.16-rc1
Git-commit: a259df36d1fbf25f0e4f649fdb84e4527e5640ed
References: bsc#1109837
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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
include/linux/ptr_ring.h | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -196,7 +196,9 @@ static inline void *__ptr_ring_peek(stru
*/
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_on
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)
@@ -536,7 +539,9 @@ static inline void ptr_ring_unconsume(st
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: