Svante Signell, on Wed 31 Aug 2016 13:24:34 +0200, wrote: > On Wed, 2016-08-31 at 12:58 +0200, Samuel Thibault wrote: > > Svante Signell, on Wed 31 Aug 2016 12:35:26 +0200, wrote: > > > > > > The attached patch changes this fixing the previous: > > > check_setpriority: can't set priority: Permission denied > > > > > > - prierr = __task_priority (task, NICE_TO_MACH_PRIORITY (prio), 1); > > > + prierr = __task_priority (task, NICE_TO_MACH_PRIORITY (prio), 0); > > Err, but then that makes change_threads false, i.e. the task_priority() > > call will not change the priorities of all threads of the task, which as > > you say is the POSIX behavior: > > So a task is equal to a thread, not a process?
No, a task is a process. See the documentation: “The priority of a task is used only for creation of new threads; a new thread's priority is set to the enclosing task's priority.” > Leading to change_threads must be TRUE (to change all threads = > process?) It must be true, yes. See the source code: otherwise it doesn't touch existing threads. > > > According to setpriority(2) and POSIX the nice value should be > > > per-process not per-thread. > > So this "fix" your testcase by making the function not do what it is > > supposed to do... > > > > Re-read your test again: it requests nice -19, i.e. something which is > > reserved to root. No wonder you are getting a permission denied. > > Explain please, I get the same output also for running as root: > check_setpriority: can't set priority: Permission denied Then there is probably also a bug about not letting root do it. But that's *another* bug. > > The > > actual bug here is that task_priority seems not to check whether the > > priority is allowed when change_threads is false. > > Tracing the call from setpriority() results in KERN_FAILURE from kern/task.c: > > if (thread_priority(thread, priority, FALSE) != KERN_SUCCESS) > ret = KERN_FAILURE; > > which falls back to the implementation of thread_priority() in kern/thread.c That's what I said, yes: task_priority seems to not do things appropriately. Samuel
