From: Willy Tarreau <w@1wt.eu>
Date: Mon, 30 Nov 2020 13:52:11 +0000 (+0100)
Subject: MINOR: task: remove __tasklet_remove_from_tasklet_list()
X-Git-Tag: v2.4-dev2~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2da4c316c2cb7b01f54ed1959e91d1799d13959c;p=thirdparty%2Fhaproxy.git

MINOR: task: remove __tasklet_remove_from_tasklet_list()

This function is only used at a single place directly within the
scheduler in run_tasks_from_lists() and it really ought not be called
by anything else, regardless of what its comment says. Let's delete
it, move the two lines directly into the call place, and take this
opportunity to factor the atomic decrement on tasks_run_queue. A comment
was added on the remaining one tasklet_remove_from_tasklet_list() to
mention the risks in using it.
---

diff --git a/include/haproxy/task.h b/include/haproxy/task.h
index e4c93fc4aa..d5cf3b1575 100644
--- a/include/haproxy/task.h
+++ b/include/haproxy/task.h
@@ -369,18 +369,9 @@ static inline void tasklet_wakeup(struct tasklet *tl)
 	tasklet_wakeup_on(tl, tl->tid);
 }
 
-/* Remove the tasklet from the tasklet list. The tasklet MUST already be there.
- * If unsure, use tasklet_remove_from_tasklet_list() instead. If used with a
- * plain task, the caller must update the task_list_size.
- * This should only be used by the thread that owns the tasklet, any other
- * thread should use tasklet_cancel().
+/* Try to remove a tasklet from the list. This call is inherently racy and may
+ * only be performed on the thread that was supposed to dequeue this tasklet.
  */
-static inline void __tasklet_remove_from_tasklet_list(struct tasklet *t)
-{
-	LIST_DEL_INIT(&t->list);
-	_HA_ATOMIC_SUB(&tasks_run_queue, 1);
-}
-
 static inline void tasklet_remove_from_tasklet_list(struct tasklet *t)
 {
 	if (MT_LIST_DEL((struct mt_list *)&t->list))
diff --git a/src/task.c b/src/task.c
index 93e30227da..d1e06ce2b4 100644
--- a/src/task.c
+++ b/src/task.c
@@ -458,10 +458,12 @@ unsigned int run_tasks_from_lists(unsigned int budgets[])
 		t->calls++;
 		sched->current = t;
 
+		_HA_ATOMIC_SUB(&tasks_run_queue, 1);
+
 		if (TASK_IS_TASKLET(t)) {
 			state = _HA_ATOMIC_XCHG(&t->state, state);
 			__ha_barrier_atomic_store();
-			__tasklet_remove_from_tasklet_list((struct tasklet *)t);
+			LIST_DEL_INIT(&((struct tasklet *)t)->list);
 			process(t, ctx, state);
 			done++;
 			sched->current = NULL;
@@ -471,7 +473,7 @@ unsigned int run_tasks_from_lists(unsigned int budgets[])
 
 		state = _HA_ATOMIC_XCHG(&t->state, state | TASK_RUNNING);
 		__ha_barrier_atomic_store();
-		__tasklet_remove_from_tasklet_list((struct tasklet *)t);
+		LIST_DEL_INIT(&((struct tasklet *)t)->list);
 
 		/* OK then this is a regular task */