Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758954AbXFMPP3 (ORCPT ); Wed, 13 Jun 2007 11:15:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757738AbXFMPPX (ORCPT ); Wed, 13 Jun 2007 11:15:23 -0400 Received: from mail.screens.ru ([213.234.233.54]:59595 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757686AbXFMPPW (ORCPT ); Wed, 13 Jun 2007 11:15:22 -0400 Date: Wed, 13 Jun 2007 19:15:30 +0400 From: Oleg Nesterov To: Roland McGrath Cc: Linus Torvalds , Andrew Morton , Linux Kernel , Satoru Takeuchi , Benjamin Herrenschmidt Subject: Re: [BUG] ptraced process waiting on syscall may return kernel internal errnos Message-ID: <20070613151530.GA232@tv-sign.ru> References: <87hcplvdkl.wl%takeuchi_satoru@jp.fujitsu.com> <20070606105900.DE5E94D0592@magilla.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070606105900.DE5E94D0592@magilla.localdomain> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2438 Lines: 66 Sorry for delay, I was completely offline, On 06/06, Roland McGrath wrote: > > [PATCH] Restrict clearing TIF_SIGPENDING > > This patch should get a few birds. It prevents sigaction calls from > clearing TIF_SIGPENDING in other threads, which could leak -ERESTART*. > It fixes ptrace_stop not to clear it, which done at the syscall exit > stop could leak -ERESTART*. It probably removes the harm from > signalfd, at least assuming it never calls dequeue_signal on kernel > threads that might have used block_all_signals. > > Signed-off-by: Roland McGrath > --- > kernel/signal.c | 40 ++++++++++++++++++++++++---------------- > 1 files changed, 24 insertions(+), 16 deletions(-) > > diff --git a/kernel/signal.c b/kernel/signal.c > index acdfc05..dc5797c 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -105,7 +105,11 @@ static int recalc_sigpending_tsk(struct > set_tsk_thread_flag(t, TIF_SIGPENDING); > return 1; > } > - clear_tsk_thread_flag(t, TIF_SIGPENDING); > + /* > + * We must never clear the flag in another thread, or in current > + * when it's possible the current syscall is returning -ERESTART*. > + * So we don't clear it here, and only callers who know they should do. > + */ > return 0; > } This breaks cancel_freezing(). Somehow we should clear TIF_SIGPENDING for kernel threads. Otherwise we may have subtle failures if try_to_freeze_tasks() fails. Also, whith this change do_sigaction()->recalc_sigpending_and_wake() doesn't make sense any longer, yes? > @@ -385,7 +391,8 @@ int dequeue_signal(struct task_struct *t > } > } > } > - recalc_sigpending_tsk(tsk); > + if (likely(tsk == current)) > + recalc_sigpending(); In theory, flush_signals(t) needs a similar change. However, it is always called with t == current. Perhaps it makes sense to make it flush_signals(void) ? Do you see any valid usage of flush_signals(t) when t != current ? (Actually, imho the same is true for dequeue_signal(). Except for signalfd.c dequeue_signal() should operate on current. Perhaps it would be a bit cleaner to have dequeue_signal_tsk(tsk) and dequeue_signal(void), the latter does recalc_sigpending). Oleg. - 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/