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authorDavid S. Miller <davem@davemloft.net>2018-01-17 08:00:25 +0300
committerDavid S. Miller <davem@davemloft.net>2018-01-17 08:10:42 +0300
commitc02b3741eb99a1ec733e6134c53ba59e43e19e97 (patch)
treeff7dd96c32dec2abe530e7101378443dabcb8962 /include/linux/ptr_ring.h
parent7018d1b3f20fb4308ed9bc577160cb8ffb79b62a (diff)
parent8cbab92dff778e516064c13113ca15d4869ec883 (diff)
downloadlinux-c02b3741eb99a1ec733e6134c53ba59e43e19e97.tar.xz
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
Overlapping changes all over. The mini-qdisc bits were a little bit tricky, however. Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/ptr_ring.h')
-rw-r--r--include/linux/ptr_ring.h14
1 files changed, 10 insertions, 4 deletions
diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 13fb06a103c6..9ca1726ff963 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -174,6 +174,15 @@ static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr)
* if they dereference the pointer - see e.g. PTR_RING_PEEK_CALL.
* If ring is never resized, and if the pointer is merely
* tested, there's no need to take the lock - see e.g. __ptr_ring_empty.
+ * However, if called outside the lock, and if some other CPU
+ * consumes ring entries at the same time, the value returned
+ * is not guaranteed to be correct.
+ * In this case - to avoid incorrectly detecting the ring
+ * as empty - the CPU consuming the ring entries is responsible
+ * for either consuming all ring entries until the ring is empty,
+ * or synchronizing with some other CPU and causing it to
+ * execute __ptr_ring_peek and/or consume the ring enteries
+ * after the synchronization point.
*/
static inline void *__ptr_ring_peek(struct ptr_ring *r)
{
@@ -182,10 +191,7 @@ static inline void *__ptr_ring_peek(struct ptr_ring *r)
return NULL;
}
-/* Note: callers invoking this in a loop must use a compiler barrier,
- * for example cpu_relax(). Callers must take consumer_lock
- * if the ring is ever resized - see e.g. ptr_ring_empty.
- */
+/* See __ptr_ring_peek above for locking rules. */
static inline bool __ptr_ring_empty(struct ptr_ring *r)
{
return !__ptr_ring_peek(r);