Greg, Would userpace_s need to have an additional function pointer for pthread_cleanup? Similar to pthread_startup?
Is the up_pthread_start/pthread_startup functions a good example to follow for how to call in user mode? Anthony On Sun, Jun 28, 2020 at 1:39 PM Gregory Nutt <spudan...@gmail.com> wrote: > Hi, Anthony, > > > > I just found an issue with using libcxx std::thread library on NuttX. The > > std::thread implementation uses pthread_key_create and > pthread_setspecific > > in order to setup a destructor that should be called to cleanup the > memory. > > Of course, it became pretty obvious what was wrong once I read the > > following comment for pthread_key_create > > > >> * Input Parameters: > >> * key - A pointer to the key to create. > >> * destructor - An optional destructor() function that may be > associated > >> * with each key that is invoked when a thread exits. > >> * > >> *However, this argument is ignored in the current** * > >> implementation.* > > > > From > > > https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxbd00/ptkycre.htm > > > > The destructor routine may be called when the thread ends. It is called > >> when a non-NULL value has been set for the key for this thread, using > >> pthread_setspecific(), and the thread: > >> > >> - Calls pthread_exit() > >> > >> > >> - Does a return from the start routine > >> > >> > >> - Is canceled because of a pthread_cancel() request. > >> > >> > > So it seems that the implementation would require the destructor to be > > called from pthread_exit and pthread_cancel. > > > > However, I'm still uncertain where in the order of operations the > > destructor should be called. Before or after pthread_completejoin? > Before > > or after pthread_mutex_inconsistent? > > > > Looking for some guidance before I start working on a fix. > A complication is that the destructor must run in user-mode in the > user-address space. pthread_exit() runs entirely in kernel mode in the > kernel address space. This is not a critical critical for the FLAT > build since everything runs in a flat address space and everything runs > in kernel mode. But this is a probleml for the PROTECTED and KERNEL > builds. Having the destructor running is kernel mode would be a major > security hole. > > The same is true of pthread_cleanup() routines and the some solution > would be required. See issue # 1263, > https://github.com/apache/incubator-nuttx/issues/1263. That solution > would involve: > > 1. Add the pthread destructor functions to the TLS data structure, and > > 2. Move a portion of the pthread_cleanup logic into libs/libc/pthread: > That portion would do the pthread_cleanup callbacks and the > pthread-specific data desctructor calls while still in user mode. Then > trap into the kernel complete the find stages of the pthread exit logic. > > Greg > > >
