Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936335AbXFGD3p (ORCPT ); Wed, 6 Jun 2007 23:29:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755631AbXFGD3h (ORCPT ); Wed, 6 Jun 2007 23:29:37 -0400 Received: from gate.crashing.org ([63.228.1.57]:42485 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754214AbXFGD3g (ORCPT ); Wed, 6 Jun 2007 23:29:36 -0400 Subject: Re: signalfd API issues (was Re: [PATCH/RFC] signal races/bugs, losing TIF_SIGPENDING and other woes) From: Benjamin Herrenschmidt To: Jeff Dike Cc: Paul Mackerras , Nicholas Miell , Davide Libenzi , Linus Torvalds , Linux Kernel list , Andrew Morton In-Reply-To: <20070607022002.GA11977@c2.user-mode-linux.org> References: <1181023787.2785.14.camel@entropy> <1181028453.31677.127.camel@localhost.localdomain> <1181087462.2788.8.camel@entropy> <1181088936.2788.10.camel@entropy> <1181091523.2788.28.camel@entropy> <1181098204.31677.158.camel@localhost.localdomain> <20070606125259.GA5491@c2.user-mode-linux.org> <18023.14494.889739.567439@cargo.ozlabs.ibm.com> <20070607022002.GA11977@c2.user-mode-linux.org> Content-Type: text/plain Date: Thu, 07 Jun 2007 13:29:23 +1000 Message-Id: <1181186963.14818.15.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.10.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1080 Lines: 24 On Wed, 2007-06-06 at 22:20 -0400, Jeff Dike wrote: > On Thu, Jun 07, 2007 at 08:43:42AM +1000, Paul Mackerras wrote: > > What Ben was talking about was stealing a synchronous SEGV from a task > > without stopping it, and as Ben says that makes no sense. > > Intercepting a signal and stopping the task is reasonable, and that is > > what ptrace does, and I assume also UML. > > It is, but I can also see UML stealing the SEGV from the child. The > UML skas does this - a ptrace extension, PTRACE_FAULTINFO, is used to > extract page fault information from the child, and other pieces of the > patch are used to fix the fault without the child continuing until > it's fixed. So, in this case, the child never sees the SEGV. But you use ptrace and don't steal signals with dequeue_signal() on a live other task, which is ok. Ben. - 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/