Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752749Ab3IVUKV (ORCPT ); Sun, 22 Sep 2013 16:10:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21491 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751569Ab3IVUKU (ORCPT ); Sun, 22 Sep 2013 16:10:20 -0400 Date: Sun, 22 Sep 2013 22:03:54 +0200 From: Oleg Nesterov To: Peter Hurley Cc: Andrew Morton , Greg Kroah-Hartman , Jiri Slaby , Linus Torvalds , codonell , Eduard Benes , Karel Srot , Matt Newsome , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] tty: disassociate_ctty() sends the extra SIGCONT Message-ID: <20130922200354.GA4865@redhat.com> References: <20130915155006.GA11913@redhat.com> <20130915155026.GA11917@redhat.com> <5238BDEC.1070400@hurleysoftware.com> <20130921183436.GA13418@redhat.com> <523E00A3.5050507@hurleysoftware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <523E00A3.5050507@hurleysoftware.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2327 Lines: 67 On 09/21, Peter Hurley wrote: > > On 09/21/2013 02:34 PM, Oleg Nesterov wrote: >> >> do_each_pid_task(tty->session, PIDTYPE_SID, p) { >> spin_lock_irq(&p->sighand->siglock); >> if (p->signal->tty == tty) { >> p->signal->tty = NULL; >> /* We defer the dereferences outside fo >> the tasklist lock */ >> refs++; >> } >> if (!p->signal->leader) { >> spin_unlock_irq(&p->sighand->siglock); >> continue; >> } >> __group_send_sig_info(SIGHUP, SEND_SIG_PRIV, p); >> __group_send_sig_info(SIGCONT, SEND_SIG_PRIV, p); >> put_pid(p->signal->tty_old_pgrp); /* A noop */ >> spin_lock(&tty->ctrl_lock); >> tty_pgrp = get_pid(tty->pgrp); >> >> I guess this can happen only once, so we could even add WARN_ON(tty_pgrp) >> before get_pid(). But this look confusing, as if we can do get_pid() >> multiple times and leak tty->pgrp. >> >> if (tty->pgrp) >> p->signal->tty_old_pgrp = get_pid(tty->pgrp); >> >> else? We already did put_pid(tty_old_pgrp), we should clear it. >> >> IOW, do you think the patch below makes sense or I missed something? >> Just curious. > > The code block you're referring to only executes once because there is > only one session leader. I understand, and I even mentioned this above. My point was, this _looks_ confusing, and the patch I sent makes it more clean. And what about ->tty_old_pgrp? I still think that at least the patch below makes sense. If tty->pgrp == NULL is not possible here (I do not know), then why do we check? Otherwise ->tty_old_pgrp != NULL looks certainly wrong after put_pid(). Oleg. --- x/drivers/tty/tty_io.c +++ x/drivers/tty/tty_io.c @@ -569,8 +569,7 @@ static int tty_signal_session_leader(str put_pid(p->signal->tty_old_pgrp); /* A noop */ spin_lock(&tty->ctrl_lock); tty_pgrp = get_pid(tty->pgrp); - if (tty->pgrp) - p->signal->tty_old_pgrp = get_pid(tty->pgrp); + p->signal->tty_old_pgrp = get_pid(tty->pgrp); spin_unlock(&tty->ctrl_lock); spin_unlock_irq(&p->sighand->siglock); } while_each_pid_task(tty->session, PIDTYPE_SID, p); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/