On Fri, Oct 30, 2020 at 09:15:39PM +0000, Martin Wilck wrote: > On Fri, 2020-10-23 at 16:15 -0500, Benjamin Marzinski wrote: > > The multipathd tur checker thread is designed to be able to finish at > > any time, even after the tur checker itself has been freed. The > > multipathd shutdown code makes sure all the checkers have been freed > > before freeing the checker_class and calling dlclose() to unload the > > DSO, but this doesn't guarantee that the checker threads have > > finished. > > If one hasn't, the DSO will get unloaded while the thread still > > running > > code from it, causing a segfault. Unfortunately, it's not possible to > > be > > sure that all tur checker threads have ended during shutdown, without > > making them joinable. > > > > However, since libmultipath will never be reinitialized after it has > > been uninitialzed, not dlclosing the tur checker DSO once a thread is > > started has minimal cost (keeping the DSO code around until the > > program > > exits, which usually happens right after freeing the checkers). > > I'm not against this, but have you considered using an atomic refcount > for the DSO? With every tur thread starting, we could increase it, and > decrease it in the cleanup function of the thread when it exits. That > should be safe. If the refcount was positive when we exit, we could > refrain from unloading the DSO. I tried exactly that, and I would still get crashes, even if it put the code that decrements the atomic variable in a function that's not part of the DSO, and put a pthread_exit() before the final pthread_cleanup_pop() that would decrement it in tur_thread, so that after the cleanup code is called the thread should never return to code that is in the DSO. I had to add sleeps in code to force various orderings, but I couldn't find any way that worked for all possible orderings. I would love it if this worked, and you're free to try, but I could not get this method to work. -Ben > Regards, > Martin -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
