[lxc-devel] [PATCH] fix console deadlocks

[Stéphane Graber]

On Fri, Sep 20, 2013 at 02:48:40PM -0500, Serge Hallyn 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
> lock then we should probably introduce a new lock - maybe held
> for the duration of a lxc-start with console or a lxc-console.
> Actually that's probably a good idea...  But here I just drop
> the locks which make lxc-start-ephemeral deadlock.
> 
> Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>

Acked-by: Stéphane Graber <stgraber at ubuntu.com>

> ---
>  src/lxc/console.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/src/lxc/console.c b/src/lxc/console.c
> index a32e9cf..78be403 100644
> --- a/src/lxc/console.c
> +++ b/src/lxc/console.c
> @@ -103,13 +103,10 @@ void lxc_console_sigwinch(int sig)
>  	struct lxc_list *it;
>  	struct lxc_tty_state *ts;
>  
> -	process_lock();
> -
>  	lxc_list_for_each(it, &lxc_ttys) {
>  		ts = it->elem;
>  		lxc_console_winch(ts);
>  	}
> -	process_unlock();
>  }
>  
>  static int lxc_console_cb_sigwinch_fd(int fd, void *cbdata,
> @@ -423,7 +420,6 @@ int lxc_console_allocate(struct lxc_conf *conf, int sockfd, int *ttyreq)
>  	struct lxc_tty_info *tty_info = &conf->tty_info;
>  	struct lxc_console *console = &conf->console;
>  
> -	process_lock();
>  	if (*ttyreq == 0) {
>  		if (lxc_console_peer_proxy_alloc(console, sockfd) < 0)
>  			goto out;
> @@ -458,7 +454,6 @@ out_tty:
>  	tty_info->pty_info[ttynum - 1].busy = sockfd;
>  	masterfd = tty_info->pty_info[ttynum - 1].master;
>  out:
> -	process_unlock();
>  	return masterfd;
>  }
>  
> @@ -476,7 +471,6 @@ void lxc_console_free(struct lxc_conf *conf, int fd)
>  	struct lxc_tty_info *tty_info = &conf->tty_info;
>  	struct lxc_console *console = &conf->console;
>  
> -	process_lock();
>  	for (i = 0; i < tty_info->nbtty; i++) {
>  		if (tty_info->pty_info[i].busy == fd)
>  			tty_info->pty_info[i].busy = 0;
> @@ -486,7 +480,6 @@ void lxc_console_free(struct lxc_conf *conf, int fd)
>  		lxc_mainloop_del_handler(console->descr, console->peerpty.slave);
>  		lxc_console_peer_proxy_free(console);
>  	}
> -	process_unlock();
>  }
>  
>  static void lxc_console_peer_default(struct lxc_console *console)
> @@ -713,9 +706,7 @@ int lxc_console(struct lxc_container *c, int ttynum,
>  		return -1;
>  	}
>  
> -	process_lock();
>  	ttyfd = lxc_cmd_console(c->name, &ttynum, &masterfd, c->config_path);
> -	process_unlock();
>  	if (ttyfd < 0) {
>  		ret = ttyfd;
>  		goto err1;
> @@ -770,9 +761,7 @@ int lxc_console(struct lxc_container *c, int ttynum,
>  		goto err4;
>  	}
>  
> -	process_lock();
>  	ret = lxc_mainloop(&descr, -1);
> -	process_unlock();
>  	if (ret) {
>  		ERROR("mainloop returned an error");
>  		goto err4;
> -- 
> 1.8.3.2
> 
> 
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-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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