BUG/MINOR: tasks: make sure never to exceed max_processed

We want to be sure not to exceed max_processed. It can actually go
slightly negative due to the rounding applied to ratios, but we must
refrain from processing too many tasks if it's already low.

This became particularly relevant since recent commit 5c8be272c ("MEDIUM:
tasks: also process late wakeups in process_runnable_tasks()") which was
merged into 2.2-dev10. No backport is needed.

diff --git a/src/task.c b/src/task.c
index 500223f185bf324c0adb34a42ec0244e638ce63e..2097555f1f97ccc2c1287bfba5130b2b5718082a 100644 (file)
--- a/src/task.c
+++ b/src/task.c
@@ -448,8 +448,10 @@ void process_runnable_tasks()
                LIST_SPLICE_END_DETACHED(&sched->tasklets[TL_URGENT], (struct list *)tmp_list);
 
        /* run up to max_processed/3 urgent tasklets */
-       done = run_tasks_from_list(&tt->tasklets[TL_URGENT], (max_processed + 2) / 3);
-       max_processed -= done;
+       if (max_processed > 0) {
+               done = run_tasks_from_list(&tt->tasklets[TL_URGENT], (max_processed + 2) / 3);
+               max_processed -= done;
+       }
 
        /* pick up to max_processed/2 (~=3/4*(max_processed-done)) regular tasks from prio-ordered run queues */
 
@@ -518,15 +520,19 @@ void process_runnable_tasks()
        }
 
        /* run between 0.4*max_processed and max_processed/2 regular tasks */
-       done = run_tasks_from_list(&tt->tasklets[TL_NORMAL], (3 * max_processed + 3) / 4);
-       max_processed -= done;
+       if (max_processed > 0) {
+               done = run_tasks_from_list(&tt->tasklets[TL_NORMAL], (3 * max_processed + 3) / 4);
+               max_processed -= done;
+       }
 
        /* run between max_processed/4 and max_processed bulk tasklets */
-       done = run_tasks_from_list(&tt->tasklets[TL_BULK], max_processed);
-       max_processed -= done;
+       if (max_processed > 0) {
+               done = run_tasks_from_list(&tt->tasklets[TL_BULK], max_processed);
+               max_processed -= done;
+       }
 
        /* some tasks may have woken other ones up */
-       if (max_processed && thread_has_tasks())
+       if (max_processed > 0 && thread_has_tasks())
                goto not_done_yet;
 
        if (!LIST_ISEMPTY(&sched->tasklets[TL_URGENT]) |