Hi, This question arises during the review of one PRs. Indeed, it seems that ECANCELED should never be returned to the app because leave_cancellation_point() should terminate the task; however there are quite a few places in code that check ECANCELED returned by semaphore. Those are: - mm_takesemaphore: DEBUGASSERT(ret == -EINTR || ret == -ECANCELED); - modlib_registry_lock: DEBUGASSERT(_SEM_ERRNO(ret) == EINTR || _SEM_ERRNO(ret) == ECANCELED); - dns_semtake: DEBUGASSERT(errcode == EINTR || errcode == ECANCELED); - lib_take_semaphore: DEBUGASSERT(_SEM_ERRNO(ret) == EINTR ||SEM_ERRNO(ret) == ECANCELED); - lib_stream_semtake: DEBUGASSERT(_SEM_ERRNO(ret) == EINTR ||SEM_ERRNO(ret) == ECANCELED); - get_base62: DEBUGASSERT(_SEM_ERRNO(ret) == EINTR || _SEM_ERRNO(ret) == ECANCELED); - tz_semtake: DEBUGASSERT(errcode == EINTR || errcode == ECANCELED); - nxf_list_lock: DEBUGASSERT(errorcode == EINTR || errorcode == ECANCELED); - nxf_cache_lock: DEBUGASSERT(errorcode == EINTR || errorcode == ECANCELED); - nxmu_semtake: DEBUGASSERT(_SEM_ERRNO(ret) == EINTR || _SEM_ERRNO(ret) == ECANCELED); - and few other places
The _SEM_WAIT can be either nxsem_wait or sem_wait, so maybe those checks are targeting the nxsem_wait case and not sem_wait. Maybe someone can educate me on that because in all those use cases code is spinning on while ((ret = _SEM_WAIT(sem)) < 0). Best regards, Petro чт, 26 трав. 2022 р. о 16:42 Gregory Nutt <spudan...@gmail.com> пише: > > > I haven't looked at that code in a long time. But I believe that the > > ECANCELED error is never returned to the application. If a thread is > > canceled, that error is caught by the cancellation point logic and the > > thread is terminated before it ever returns to the application. > > > > If cancellation points are not enabled then the ECANCELED error shoul > > never be generated. > > There are only a couple of places where ECANCELED can be returned to the > caller (aio_cancel(), timerfd_create(), a probably others. > > I would not be surprised if there are places in the code where ECANCELED > could be returned to the application inappropriately. But these would > all be errors and should be fixed. No testing has been done to see if > we can force and erroneous ECANCELED return. > > For example, what would happen if you enable cancellation points, but > disable cancellation, then call a function that requires cancellation > support? The correct result is that the cancellation attempt should > fail and the thread should continue running. > > Returning EINTR would be wrong in any case. > > >
