ringbuffer: use atomic ops on ringbuffer chunk magic

The ringbuffer protocol uses the chunk magic number to indicate to the
other side what state a chunk is in.  It's therefore important to use
strongly ordered memory writes to make sure that neither the compiler
nor the CPU change the apparent order of the writes, since that would
result in corrupted messages.

Signed-off-by: Angus Salkeld <asalkeld@redhat.com>

lib/ringbuffer.c

@@ -86,11 +86,11 @@ do {							\
 #define QB_RB_CHUNK_MAGIC_DEAD		0xD0D0D0D0
 #define QB_RB_CHUNK_MAGIC_ALLOC		0xA110CED0
 #define QB_RB_CHUNK_SIZE_GET(rb, pointer) \
-	rb->shared_data[pointer]
+	qb_atomic_int_get(&rb->shared_data[pointer])
 #define QB_RB_CHUNK_MAGIC_GET(rb, pointer) \
-	rb->shared_data[(pointer + 1) % rb->shared_hdr->word_size]
+	qb_atomic_int_get(&rb->shared_data[(pointer + 1) % rb->shared_hdr->word_size])
 #define QB_RB_CHUNK_MAGIC_SET(rb, pointer, new_val) \
-	rb->shared_data[(pointer + 1) % rb->shared_hdr->word_size] = new_val;
+	qb_atomic_int_set(&rb->shared_data[(pointer + 1) % rb->shared_hdr->word_size], new_val)
 #define QB_RB_CHUNK_DATA_GET(rb, pointer) \
 	&rb->shared_data[(pointer + QB_RB_CHUNK_HEADER_WORDS) % rb->shared_hdr->word_size]