Quoting Dwight Engen (dwight.en...@oracle.com): > On Fri, 20 Sep 2013 15:26:47 -0500 > Serge Hallyn <serge.hal...@ubuntu.com> wrote: > > > Quoting Dwight Engen (dwight.en...@oracle.com): > > > On Fri, 20 Sep 2013 14:48:40 -0500 > > > Serge Hallyn <serge.hal...@ubuntu.com> wrote: > > > > > > > These might be a bit controversial. The process lock was held > > > > for some long periods of time for tweaking consoles. These > > > > can deadlock with some of lock holds I introduced recently. I > > > > would argue that if two threads are fighting over the console, > > > > you're gonna have trouble anyway, and the process locks here > > > > weren't saving us from anything. If we want to do a console > > > > > > Are we sure we can walk/modify the lxc_ttys list lockless? I agree > > > > Yeah we do need to lock those. But I don't think there's a rush for > > it. > > > > > threaded console use is "interesting", but I don't think we want > > > list corruption. Of course we don't want deadlocks either :) > > > > So which do you think would be better - introduce a lxc_ttys lock > > specifically, or introduce a general 'console' mutex which is taken > > any time we open a console or edit the lxc_ttys? > > Hmm, good question. I think that lxc_console_allocate() and > lxc_console_free() are only called from lxc today when handling commands > so they are not going to be used from a threaded context anyways. But > the symbols are available so someone could write a threaded program and > call them and race on the .busy indicator for example. I think we > minimally need the list stuff locked, but I'm not sure what else. I > have not really tested multithreaded console use. > > Just out of curiosity, this is deadlocking because the process lock is > already held when console routines are getting called and the process > lock mutex isn't recursive?
At the least lxc_console_allocate() was taking process_lock(), then calling lxc_console_peer_proxy_alloc() which also calls process_lock. I could have decided not to take the lock in lxc_console_peer_proxy_alloc(), but that seems more wrong and be less maintainable. -serge ------------------------------------------------------------------------------ LIMITED TIME SALE - Full Year of Microsoft Training For Just $49.99! 1,500+ hours of tutorials including VisualStudio 2012, Windows 8, SharePoint 2013, SQL 2012, MVC 4, more. BEST VALUE: New Multi-Library Power Pack includes Mobile, Cloud, Java, and UX Design. Lowest price ever! Ends 9/20/13. http://pubads.g.doubleclick.net/gampad/clk?id=58041151&iu=/4140/ostg.clktrk _______________________________________________ Lxc-devel mailing list Lxc-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lxc-devel
