void _lib_ring_buffer_switch_remote(struct lib_ring_buffer *buf,
enum switch_mode mode);
+static
+int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan)
+{
+ unsigned long consumed_old, consumed_idx, commit_count, write_offset;
+
+ consumed_old = atomic_long_read(&buf->consumed);
+ consumed_idx = subbuf_index(consumed_old, chan);
+ commit_count = v_read(config, &buf->commit_cold[consumed_idx].cc_sb);
+ /*
+ * No memory barrier here, since we are only interested
+ * in a statistically correct polling result. The next poll will
+ * get the data is we are racing. The mb() that ensures correct
+ * memory order is in get_subbuf.
+ */
+ write_offset = v_read(config, &buf->offset);
+
+ /*
+ * Check that the subbuffer we are trying to consume has been
+ * already fully committed.
+ */
+
+ if (((commit_count - chan->backend.subbuf_size)
+ & chan->commit_count_mask)
+ - (buf_trunc(consumed_old, chan)
+ >> chan->backend.num_subbuf_order)
+ != 0)
+ return 0;
+
+ /*
+ * Check that we are not about to read the same subbuffer in
+ * which the writer head is.
+ */
+ if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_old, chan)
+ == 0)
+ return 0;
+
+ return 1;
+}
+
/*
* Must be called under cpu hotplug protection.
*/
}
EXPORT_SYMBOL_GPL(lib_ring_buffer_reserve_slow);
+static
+void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ unsigned long commit_count,
+ unsigned long idx)
+{
+ if (config->oops == RING_BUFFER_OOPS_CONSISTENCY)
+ v_set(config, &buf->commit_hot[idx].seq, commit_count);
+}
+
+void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan,
+ unsigned long offset,
+ unsigned long commit_count,
+ unsigned long idx,
+ u64 tsc)
+{
+ unsigned long old_commit_count = commit_count
+ - chan->backend.subbuf_size;
+
+ /*
+ * If we succeeded at updating cc_sb below, we are the subbuffer
+ * writer delivering the subbuffer. Deals with concurrent
+ * updates of the "cc" value without adding a add_return atomic
+ * operation to the fast path.
+ *
+ * We are doing the delivery in two steps:
+ * - First, we cmpxchg() cc_sb to the new value
+ * old_commit_count + 1. This ensures that we are the only
+ * subbuffer user successfully filling the subbuffer, but we
+ * do _not_ set the cc_sb value to "commit_count" yet.
+ * Therefore, other writers that would wrap around the ring
+ * buffer and try to start writing to our subbuffer would
+ * have to drop records, because it would appear as
+ * non-filled.
+ * We therefore have exclusive access to the subbuffer control
+ * structures. This mutual exclusion with other writers is
+ * crucially important to perform record overruns count in
+ * flight recorder mode locklessly.
+ * - When we are ready to release the subbuffer (either for
+ * reading or for overrun by other writers), we simply set the
+ * cc_sb value to "commit_count" and perform delivery.
+ *
+ * The subbuffer size is least 2 bytes (minimum size: 1 page).
+ * This guarantees that old_commit_count + 1 != commit_count.
+ */
+
+ /*
+ * Order prior updates to reserve count prior to the
+ * commit_cold cc_sb update.
+ */
+ smp_wmb();
+ if (likely(v_cmpxchg(config, &buf->commit_cold[idx].cc_sb,
+ old_commit_count, old_commit_count + 1)
+ == old_commit_count)) {
+ /*
+ * Start of exclusive subbuffer access. We are
+ * guaranteed to be the last writer in this subbuffer
+ * and any other writer trying to access this subbuffer
+ * in this state is required to drop records.
+ */
+ v_add(config,
+ subbuffer_get_records_count(config,
+ &buf->backend, idx),
+ &buf->records_count);
+ v_add(config,
+ subbuffer_count_records_overrun(config,
+ &buf->backend,
+ idx),
+ &buf->records_overrun);
+ config->cb.buffer_end(buf, tsc, idx,
+ lib_ring_buffer_get_data_size(config,
+ buf,
+ idx));
+
+ /*
+ * Increment the packet counter while we have exclusive
+ * access.
+ */
+ subbuffer_inc_packet_count(config, &buf->backend, idx);
+
+ /*
+ * Set noref flag and offset for this subbuffer id.
+ * Contains a memory barrier that ensures counter stores
+ * are ordered before set noref and offset.
+ */
+ lib_ring_buffer_set_noref_offset(config, &buf->backend, idx,
+ buf_trunc_val(offset, chan));
+
+ /*
+ * Order set_noref and record counter updates before the
+ * end of subbuffer exclusive access. Orders with
+ * respect to writers coming into the subbuffer after
+ * wrap around, and also order wrt concurrent readers.
+ */
+ smp_mb();
+ /* End of exclusive subbuffer access */
+ v_set(config, &buf->commit_cold[idx].cc_sb,
+ commit_count);
+ /*
+ * Order later updates to reserve count after
+ * the commit_cold cc_sb update.
+ */
+ smp_wmb();
+ lib_ring_buffer_vmcore_check_deliver(config, buf,
+ commit_count, idx);
+
+ /*
+ * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
+ */
+ if (config->wakeup == RING_BUFFER_WAKEUP_BY_WRITER
+ && atomic_long_read(&buf->active_readers)
+ && lib_ring_buffer_poll_deliver(config, buf, chan)) {
+ wake_up_interruptible(&buf->read_wait);
+ wake_up_interruptible(&chan->read_wait);
+ }
+
+ }
+}
+EXPORT_SYMBOL_GPL(lib_ring_buffer_check_deliver_slow);
+
int __init init_lib_ring_buffer_frontend(void)
{
int cpu;
projects / lttng-modules.git / blobdiff