From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751263AbeDCNtA (ORCPT ); Tue, 3 Apr 2018 09:49:00 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:39852 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751048AbeDCNs7 (ORCPT ); Tue, 3 Apr 2018 09:48:59 -0400 Date: Tue, 3 Apr 2018 06:48:54 -0700 From: Matthew Wilcox To: Chris Wilson Cc: dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Souptick Joarder , linux-kernel@vger.kernel.org Subject: Re: Signal handling in a page fault handler Message-ID: <20180403134854.GA28565@bombadil.infradead.org> References: <20180402141058.GL13332@bombadil.infradead.org> <152275879566.32747.9293394837417347482@mail.alporthouse.com> <20180403131025.GF5832@bombadil.infradead.org> <152276164305.32747.4969221700358143640@mail.alporthouse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <152276164305.32747.4969221700358143640@mail.alporthouse.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 03, 2018 at 02:20:43PM +0100, Chris Wilson wrote: > Quoting Matthew Wilcox (2018-04-03 14:10:25) > > On Tue, Apr 03, 2018 at 01:33:15PM +0100, Chris Wilson wrote: > > > Quoting Matthew Wilcox (2018-04-02 15:10:58) > > > > I don't think the graphics drivers really want to be interrupted by > > > > any signal. > > > > > > Assume the worst case and we may block for 10s. Even a 10ms delay may be > > > unacceptable to some signal handlers (one presumes). For the number one > > > ^C usecase, yes that may be reduced to only bother if it's killable, but > > > I wonder if there are not timing loops (e.g. sigitimer in Xorg < 1.19) > > > that want to be able to interrupt random blockages. > > > > Ah, setitimer / SIGALRM. So what do we want to have happen if that > > signal handler touches the mmaped device memory? > > Burn in a great ball of fire :) Isn't that what usually happens if you > do anything in a signal handler? I don't know. My mummy and daddy don't let me play with sharp things like signals. > Hmm, if SIGBUS has a handler does that count as a killable signal? The > ddx does have code to service SIGBUS emitted when accessing the mmapped > pointer that may result from the page insertion failing with no memory > (or other random error). There we stop accessing via the pointer and > use another indirect method. Any signal with a handler is non-fatal, and so a call to mutex_lock_killable() would not return if SIGBUS was delivered to a thread blocking in a page fault. mutex_lock_interruptible() would return -EINTR.