Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751903AbWJWLQz (ORCPT ); Mon, 23 Oct 2006 07:16:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751911AbWJWLQz (ORCPT ); Mon, 23 Oct 2006 07:16:55 -0400 Received: from amsfep17-int.chello.nl ([213.46.243.15]:5529 "EHLO amsfep12-int.chello.nl") by vger.kernel.org with ESMTP id S1751903AbWJWLQz (ORCPT ); Mon, 23 Oct 2006 07:16:55 -0400 Subject: Re: [PATCH] do_task_stat: don't take tty_mutex From: Peter Zijlstra To: Oleg Nesterov Cc: Andrew Morton , Alan Cox , linux-kernel@vger.kernel.org In-Reply-To: <20061022155735.GA10491@oleg> References: <20061022155735.GA10491@oleg> Content-Type: text/plain Date: Mon, 23 Oct 2006 13:16:41 +0200 Message-Id: <1161602202.5230.91.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1881 Lines: 56 On Sun, 2006-10-22 at 19:57 +0400, Oleg Nesterov wrote: > Depends on > tty-signal-tty-locking.patch > > ->signal->tty is protected by ->siglock, no need to take the global tty_mutex. > > Signed-off-by: Oleg Nesterov ->siglock protects the value of ->signal->tty, not memory it points to; however since destroying the tty also means clearing all ->signal->tty references, which means taking all ->siglocks, just holding the ->siglock around this piece of code looks sufficient indeed. Acked-by: Peter Zijlstra > --- rc2-mm2/fs/proc/array.c~ 2006-10-22 19:28:17.000000000 +0400 > +++ rc2-mm2/fs/proc/array.c 2006-10-22 19:45:52.000000000 +0400 > @@ -346,20 +346,13 @@ static int do_task_stat(struct task_stru > sigemptyset(&sigcatch); > cutime = cstime = utime = stime = cputime_zero; > > - mutex_lock(&tty_mutex); > rcu_read_lock(); > if (lock_task_sighand(task, &flags)) { > struct signal_struct *sig = task->signal; > - struct tty_struct *tty = sig->tty; > > - if (tty) { > - /* > - * sig->tty is not stable, but tty_mutex > - * protects us from release_dev(tty) > - */ > - barrier(); > - tty_pgrp = tty->pgrp; > - tty_nr = new_encode_dev(tty_devnum(tty)); > + if (sig->tty) { > + tty_pgrp = sig->tty->pgrp; > + tty_nr = new_encode_dev(tty_devnum(sig->tty)); > } > > num_threads = atomic_read(&sig->count); > @@ -395,7 +388,6 @@ static int do_task_stat(struct task_stru > unlock_task_sighand(task, &flags); > } > rcu_read_unlock(); > - mutex_unlock(&tty_mutex); > > if (!whole || num_threads<2) > wchan = get_wchan(task); > - 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/