- if (mode == SWITCH_FLUSH || off > 0) {
- if (unlikely(off == 0)) {
- /*
- * A final flush that encounters an empty
- * sub-buffer cannot switch buffer if a
- * reader is located within this sub-buffer.
- * Anyway, the purpose of final flushing of a
- * sub-buffer at offset 0 is to handle the case
- * of entirely empty stream.
- */
- if (unlikely(subbuf_trunc(offsets->begin, chan)
- - subbuf_trunc((unsigned long)
- atomic_long_read(&buf->consumed), chan)
- >= chan->backend.buf_size))
- return -1;
- /*
- * The client does not save any header information.
- * Don't switch empty subbuffer on finalize, because it
- * is invalid to deliver a completely empty subbuffer.
- */
- if (!config->cb.subbuffer_header_size())
+ if (mode != SWITCH_FLUSH && !off)
+ return -1; /* we do not have to switch : buffer is empty */
+
+ if (unlikely(off == 0)) {
+ unsigned long sb_index, commit_count;
+
+ /*
+ * We are performing a SWITCH_FLUSH. There may be concurrent
+ * writes into the buffer if e.g. invoked while performing a
+ * snapshot on an active trace.
+ *
+ * If the client does not save any header information (sub-buffer
+ * header size == 0), don't switch empty subbuffer on finalize,
+ * because it is invalid to deliver a completely empty
+ * subbuffer.
+ */
+ if (!config->cb.subbuffer_header_size())
+ return -1;
+
+ /* Test new buffer integrity */
+ sb_index = subbuf_index(offsets->begin, chan);
+ commit_count = v_read(config,
+ &buf->commit_cold[sb_index].cc_sb);
+ reserve_commit_diff =
+ (buf_trunc(offsets->begin, chan)
+ >> chan->backend.num_subbuf_order)
+ - (commit_count & chan->commit_count_mask);
+ if (likely(reserve_commit_diff == 0)) {
+ /* Next subbuffer not being written to. */
+ if (unlikely(config->mode != RING_BUFFER_OVERWRITE &&
+ subbuf_trunc(offsets->begin, chan)
+ - subbuf_trunc((unsigned long)
+ atomic_long_read(&buf->consumed), chan)
+ >= chan->backend.buf_size)) {
+ /*
+ * We do not overwrite non consumed buffers
+ * and we are full : don't switch.
+ */