On 18/01/22 12:10, Eric W. Biederman wrote: > Valentin Schneider <valentin.schneider@xxxxxxx> writes: >> >> Alternatively, TASK_RTLOCK_WAIT could be masqueraded as >> TASK_(UN)INTERRUPTIBLE when reported to userspace - it is actually somewhat >> similar, unlike TASK_IDLE vs TASK_UNINTERRUPTIBLE for instance. The >> handling in get_task_state() will be fugly, but it might be preferable over >> exposing a detail userspace might not need to be made aware of? > > Right. > > Frequently I have seen people do a cost/benefit analysis. > > If the benefit is enough, and tracking down the userspace programs that > need to be verified to work with the change is inexpensive enough the > change is made. Always keeping in mind that if something was missed and > the change causes a regression the change will need to be reverted. > > If there is little benefit or the cost to track down userspace is great > enough the work is put in to hide the change from userspace. Just > because it is too much trouble to expose it to userspace. > > I honestly don't have any kind of sense about how hard it is to verify > that a userspace regression won't result from a change like this. I > just know that the question needs to be asked. > I see it as: does it actually make sense to expose a new state? All the information this is conveying is: "this task took a lock that is substituted by a sleepable lock under PREEMPT_RT". Now that you brought this up, I don't really see much value in this vs just conveying that the task is sleeping on a lock, i.e. just report the same as if it had gone through rt_mutex_lock(), aka: --- diff --git a/include/linux/sched.h b/include/linux/sched.h index d00837d12b9d..ac7b3eef4a61 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1626,6 +1626,14 @@ static inline unsigned int __task_state_index(unsigned int tsk_state, if (tsk_state == TASK_IDLE) state = TASK_REPORT_IDLE; + /* + * We're lying here, but rather than expose a completely new task state + * to userspace, we can make this appear as if the task had gone through + * a regular rt_mutex_lock() call. + */ + if (tsk_state == TASK_RTLOCK_WAIT) + state = TASK_UNINTERRUPTIBLE; + return fls(state); }