Move to kernel style SPDX license identifiers

[lttng-ust.git] / libringbuffer / frontend_internal.h

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 4ad921ec0ec8263086cddbf1c11044110dc672f6..9c6a8db78ecdd50dc9d510e99cfdc182fa868a18 100644 (file)
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -1,39 +1,20 @@
-#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
-#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
-
 /*
- * libringbuffer/frontend_internal.h
- *
- * Ring Buffer Library Synchronization Header (internal helpers).
+ * SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
  *
  * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; only
- * version 2.1 of the License.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
- *
- * Author:
- *     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Ring Buffer Library Synchronization Header (internal helpers).
  *
  * See ring_buffer_frontend.c for more information on wait-free algorithms.
- *
- * Dual LGPL v2.1/GPL v2 license.
  */
 
+#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
+#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
+
 #include <urcu/compiler.h>
 #include <urcu/tls-compat.h>
 #include <signal.h>
+#include <stdint.h>
 #include <pthread.h>
 
 #include <lttng/ringbuffer-config.h>
@@ -205,6 +186,15 @@ void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
                                              consumed_new) != consumed_old));
 }
 
+/*
+ * Move consumed position to the beginning of subbuffer in which the
+ * write offset is. Should only be used on ring buffers that are not
+ * actively being written into, because clear_reader does not take into
+ * account the commit counters when moving the consumed position, which
+ * can make concurrent trace producers or consumers observe consumed
+ * position further than the write offset, which breaks ring buffer
+ * algorithm guarantees.
+ */
 static inline
 void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
                                  struct lttng_ust_shm_handle *handle)
@@ -221,12 +211,10 @@ void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
        do {
                offset = v_read(config, &buf->offset);
                consumed_old = uatomic_read(&buf->consumed);
-               if (caa_unlikely(subbuf_trunc(offset, chan)
-                             - subbuf_trunc(consumed_old, chan)
-                            > 0))
-                       consumed_new = subbuf_trunc(offset, chan);
-               else
-                       return;
+               CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
+                               - subbuf_trunc(consumed_old, chan))
+                               < 0);
+               consumed_new = subbuf_trunc(offset, chan);
        } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
                                              consumed_new) != consumed_old));
 }
@@ -260,14 +248,11 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
                                      struct lttng_ust_shm_handle *handle)
 {
        unsigned long offset, idx, commit_count;
-       struct commit_counters_hot *cc_hot = shmp_index(handle, buf->commit_hot, idx);
+       struct commit_counters_hot *cc_hot;
 
        CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
        CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 
-       if (caa_unlikely(!cc_hot))
-               return 0;
-
        /*
         * Read offset and commit count in a loop so they are both read
         * atomically wrt interrupts. By deal with interrupt concurrency by
@@ -279,6 +264,9 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
        do {
                offset = v_read(config, &buf->offset);
                idx = subbuf_index(offset, chan);
+               cc_hot = shmp_index(handle, buf->commit_hot, idx);
+               if (caa_unlikely(!cc_hot))
+                       return 0;
                commit_count = v_read(config, &cc_hot->cc);
        } while (offset != v_read(config, &buf->offset));