BUG/MINOR: stream: Properly handle "on-marked-up shutdown-backup-sessions"

shutdown-backup-sessions action for on-marked-up directive does not work anymore
since the stream_shutdown() function was modified to be async-safe.

When stream_shutdown() was modified to be async-safe, dedicated task events were
added to map the reasons to shut a stream down. SF_ERR_DOWN was mapped to
TASK_F_EVT1 and SF_ERR_KILLED was mapped to TASK_F_EVT2. The reverse mapping was
performed by process_stream() to shut the stream with the appropriate reason.

However, SF_ERR_UP reason, used by shutdown-backup-sessions action to shut a
stream down because a preferred server became available, was not mapped in the
same way. So since commit b8e3b0a18d ("BUG/MEDIUM: stream: make
stream_shutdown() async-safe"), this action is ignored and does not work
anymore.

To fix an issue, and being able to bakcport the fix, a third task event was
added. TASK_F_EVT3 is now mapped on SF_ERR_UP.

This patch should fix the issue #2848. It must be backported as far as 2.6.

doc/internals/api/scheduler.txt

@@ -221,6 +221,9 @@ state field before the call to ->process()
   - TASK_F_UEVT2       one-shot user-defined event type 2. This is application
                        specific, and reset to 0 when the handler is called.
 
+  - TASK_F_UEVT3       one-shot user-defined event type 3. This is application
+                       specific, and reset to 0 when the handler is called.
+
 In addition, a few persistent flags may be observed or manipulated by the
 application, both for tasks and tasklets:
 

include/haproxy/stream.h

@@ -389,15 +389,17 @@ static inline int stream_check_conn_timeout(struct stream *s)
  * locked one way or another so that it cannot leave (i.e. when inspecting
  * a locked list or under thread isolation). Process_stream() will recognize
  * the message and complete the job. <why> only supports SF_ERR_DOWN (mapped
- * to UEVT1) and SF_ERR_KILLED (mapped to UEVT2). Other values will just
+ * to UEVT1), SF_ERR_KILLED (mapped to UEVT2) and SF_ERR_UP (mapped to UEVT3).
- * trigger TASK_WOKEN_OTHER. The stream handler will first call function
+ * Other values will just trigger TASK_WOKEN_OTHER.
- * stream_shutdown_self() on wakeup to complete the notification.
+ * The stream handler will first call function stream_shutdown_self() on wakeup
+ * to complete the notification.
  */
 static inline void stream_shutdown(struct stream *s, int why)
 {
 	task_wakeup(s->task, TASK_WOKEN_OTHER |
 	            ((why == SF_ERR_DOWN) ? TASK_F_UEVT1 :
 	             (why == SF_ERR_KILLED) ? TASK_F_UEVT2 :
+	             (why == SF_ERR_UP) ? TASK_F_UEVT3 :
 	             0));
 }
 

include/haproxy/task-t.h

@@ -61,7 +61,8 @@
 #define TASK_F_UEVT1      0x00020000  /* one-shot user event type 1, application specific, def:0 */
 #define TASK_F_UEVT2      0x00040000  /* one-shot user event type 2, application specific, def:0 */
 #define TASK_F_WANTS_TIME 0x00080000  /* task/tasklet wants th_ctx->sched_call_date to be set */
-/* unused: 0x100000..0x80000000 */
+#define TASK_F_UEVT3      0x00100000  /* one-shot user event type 3, application specific, def:0 */
+/* unused: 0x200000..0x80000000 */
 
 /* These flags are persistent across scheduler calls */
 #define TASK_PERSISTENT   (TASK_SELF_WAKING | TASK_KILLED | \

src/stream.c

@@ -1707,6 +1707,7 @@ void stream_update_timings(struct task *t, uint64_t lat, uint64_t cpu)
  *  - TASK_WOKEN_MSG forces analysers to be re-evaluated
  *  - TASK_WOKEN_OTHER+TASK_F_UEVT1 shuts the stream down on server down
  *  - TASK_WOKEN_OTHER+TASK_F_UEVT2 shuts the stream down on active kill
+ *  - TASK_WOKEN_OTHER+TASK_F_UEVT3 shuts the stream down because a preferred backend became available
  *  - TASK_WOKEN_OTHER alone has no effect
  */
 struct task *process_stream(struct task *t, void *context, unsigned int state)
@@ -1728,9 +1729,9 @@ struct task *process_stream(struct task *t, void *context, unsigned int state)
 	activity[tid].stream_calls++;
 	stream_cond_update_cpu_latency(s);
 
-	if ((state & TASK_WOKEN_OTHER) && (state & (TASK_F_UEVT1 | TASK_F_UEVT2))) {
+	if ((state & TASK_WOKEN_OTHER) && (state & (TASK_F_UEVT1 | TASK_F_UEVT2 | TASK_F_UEVT3))) {
 		/* that an instant kill message, the reason is in _UEVT* */
-		stream_shutdown_self(s, (state & TASK_F_UEVT2) ? SF_ERR_KILLED : SF_ERR_DOWN);
+		stream_shutdown_self(s, (state & TASK_F_UEVT3) ? SF_ERR_UP : (state & TASK_F_UEVT2) ? SF_ERR_KILLED : SF_ERR_DOWN);
 	}
 
 	req = &s->req;