BUG/MEDIUM: task/h2: add an idempotent task removal fucntion
Previous commit 3ea351368 ("BUG/MEDIUM: h2: Remove the tasklet from the
task list if unsubscribing.") uncovered an issue which needs to be
addressed in the scheduler's API. The function task_remove_from_task_list()
was initially designed to remove a task from the running tasklet list from
within the scheduler, and had to be used in h2 to abort pending I/O events.
However this function was not designed to be idempotent, occasionally
causing a double removal from the tasklet list, with the second doing
nothing but affecting the apparent tasks count and making haproxy use
100% CPU on some tests consisting in stopping the client during some
transfers. The h2_unsubscribe() function can sometimes be called upon
stream exit after an error where the tasklet was possibly already
removed, so it.
This patch does 2 things :
- it renames task_remove_from_task_list() to
__task_remove_from_tasklet_list() to discourage users from calling
it. Also note the fix in the naming since it's a tasklet list and
not a task list. This function is still uesd from the scheduler.
- it adds a new, idempotent, task_remove_from_tasklet_list() function
which does nothing if the task is already not in the tasklet list.
This patch will need to be backported where the commit above is backported.
diff --git a/include/proto/task.h b/include/proto/task.h
index 0f8017d..c876e73 100644
--- a/include/proto/task.h
+++ b/include/proto/task.h
@@ -271,7 +271,10 @@
LIST_ADDQ(&task_per_thread[tid].task_list, &tl->list);
}
-static inline void task_remove_from_task_list(struct task *t)
+/* remove the task from the tasklet list. The task MUST already be there. If
+ * unsure, use task_remove_from_task_list() instead.
+ */
+static inline void __task_remove_from_tasklet_list(struct task *t)
{
LIST_DEL_INIT(&((struct tasklet *)t)->list);
task_per_thread[tid].task_list_size--;
@@ -280,6 +283,12 @@
_HA_ATOMIC_SUB(&tasks_run_queue, 1);
}
+static inline void task_remove_from_tasklet_list(struct task *t)
+{
+ if (likely(!LIST_ISEMPTY(&((struct tasklet *)t)->list)))
+ __task_remove_from_tasklet_list(t);
+}
+
/*
* Unlinks the task and adjusts run queue stats.
* A pointer to the task itself is returned.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 959bcfb..b6c2c80 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -5182,7 +5182,7 @@
sw = param;
if (h2s->send_wait == sw) {
sw->events &= ~SUB_CALL_UNSUBSCRIBE;
- task_remove_from_task_list((struct task *)h2s->send_wait->task);
+ task_remove_from_tasklet_list((struct task *)h2s->send_wait->task);
h2s->send_wait = NULL;
LIST_DEL(&h2s->list);
LIST_INIT(&h2s->list);
@@ -5270,7 +5270,7 @@
list_for_each_entry_safe(h2s, h2s_back, &h2c->sending_list, sending_list) {
LIST_DEL_INIT(&h2s->sending_list);
- task_remove_from_task_list((struct task *)h2s->send_wait->task);
+ task_remove_from_tasklet_list((struct task *)h2s->send_wait->task);
h2s->send_wait->events |= SUB_RETRY_SEND;
h2s->send_wait->events &= ~SUB_CALL_UNSUBSCRIBE;
}
diff --git a/src/task.c b/src/task.c
index 637e235..7f34bc5 100644
--- a/src/task.c
+++ b/src/task.c
@@ -416,7 +416,7 @@
t = (struct task *)LIST_ELEM(task_per_thread[tid].task_list.n, struct tasklet *, list);
state = _HA_ATOMIC_XCHG(&t->state, TASK_RUNNING);
__ha_barrier_atomic_store();
- task_remove_from_task_list(t);
+ __task_remove_from_tasklet_list(t);
ctx = t->context;
process = t->process;