On Wed, Jan 17, 2018 at 02:04:19AM +0000, Wuchongyun wrote: > On Tue, Jan 17, 2018 at 06:39:20PM +0100, Benjamin Marzinski wrote: > > On Tue, Jan 16, 2018 at 02:19:20PM +0100, Martin Wilck wrote: > > > On Tue, 2018-01-16 at 11:48 +0000, Wuchongyun wrote: > > > > Hi Martin, > > > > Sorry to forget that, actually I found that dead_client() will not > > > > be interrupt by thread cancle, because after all dead_client() > > > > calling point be done then handle_signals() have chance to be called > > > > by > > > > uxsock_listen() which will call exit_daemon() and send cancel > > > > threads signal to all child process include uxlsnr. > > > > > > Fair enough. > > > > > > > But your comments is good can make code more safer. Below is the new > > > > patch, please have a look, thanks. > > > > > > I think it's really safer whis way, should anyone see the need to > >> cancel the listener thread from another point in the code. > > > I'm confused why this is safe. After uxsock_listen() calls exit_daemon() from handle_signals(), it doesn't exit. It loops around and polls again, and could in theory find a client that has died. In fact if the client is killing multipathd via > > # multipathd shutdown > > instead of a signal, won't it be very likely that it will find a dead client when it loops right after calling exit_daemon() in cli_shutdown()? This could hit the deadlock that you noticed, where > > uxsock_cleanup() can't run because dead_client() already holding the mutex. > > Or am I missing something here? > > Hi Benjiamin, > Thanks for your comments below are my rely, thanks. > > You really found the scenario which need to add pthread_cleanup_push(cleanup_lock, &client_lock) before get lock in dead_client to avoid the dead lock: > If the client is killing multipathd via multipathd shutdown and it find a dead client when it loops right after calling exit_daemon() in cli_shutdown(), This will not hit deadlock because in dead_client before get lock we call pthread_cleanup_push(cleanup_lock, &client_lock) first, then thread cancelation happened, thread cleanup functions been pop up by reverse order: cleanup_lock() first, then uxsock_cleanup(), which make sure client_lock been release before calling uxsock_cleanup(). So it's safer in this way. I thought Martin was asking you to not add the pthread_cleanup_push/pop in dead_client, and I was trying to argue that they were necessary. But I think I just made the conversation more muddled. So yes, please add the pthread_cleanup_push/pop in dead_client. It does make the program safer. Sorry if I'm just restating what everyone had already agreed to. Thanks. -Ben > > And your next comment is right I will make another patch for this. > >Since you are now closing ux_sock in uxsock_cleanup(), you should remove the close(ux_sock) at the end of uxsock_listen(). pthread_cleanup_pop() will already take care of that. > > Regards > Chongyun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
