casaroli commented on code in PR #21393:
URL: https://github.com/apache/nuttx/pull/21393#discussion_r4452938769
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sched/sched/sched_setpriority.c:
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@@ -80,12 +80,12 @@ static inline void nxsched_running_setpriority(FAR struct
tcb_s *tcb,
* CASE 1. The new priority of the running task becomes less than or
* equal to the next highest priority ready to run task.
* CASE 2. In SMP, the affinity of tcb has changed and no longer includes
- * the current cpu.
+ * the current cpu, also when no other task is ready to run.
*/
#ifdef CONFIG_SMP
- if (nxttcb && (sched_priority <= nxttcb->sched_priority ||
- (tcb->affinity & (1 << tcb->cpu)) == 0))
+ if ((tcb->affinity & (1 << tcb->cpu)) == 0 ||
+ (nxttcb && sched_priority <= nxttcb->sched_priority))
Review Comment:
In SMP `nxttcb` is the head of the ready-to-run list (line 73), and it is
NULL when no other task is ready to run. Then the old condition is false, so a
`sched_setaffinity()` that removes the current CPU does not move the caller.
Test: a task that pins itself to each other CPU in turn still runs on its old
CPU in all 30 checks on master (qemu-armv8a:nsh_smp, 4 CPUs), and in none with
this change.
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