From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59453) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c1wxH-0004OL-Nt for qemu-devel@nongnu.org; Wed, 02 Nov 2016 10:55:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c1wxD-0004P3-Q5 for qemu-devel@nongnu.org; Wed, 02 Nov 2016 10:55:55 -0400 Received: from mail-wm0-x22a.google.com ([2a00:1450:400c:c09::22a]:34858) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1c1wxD-0004Ln-Ga for qemu-devel@nongnu.org; Wed, 02 Nov 2016 10:55:51 -0400 Received: by mail-wm0-x22a.google.com with SMTP id a197so146104765wmd.0 for ; Wed, 02 Nov 2016 07:55:39 -0700 (PDT) References: <20161021115442.18420-1-alex.bennee@linaro.org> <1776cd73-bfa5-8af8-5d76-34d9760a1664@redhat.com> <871syvxjan.fsf@linaro.org> <20161102140653.GH4693@stefanha-x1.localdomain> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <20161102140653.GH4693@stefanha-x1.localdomain> Date: Wed, 02 Nov 2016 14:55:37 +0000 Message-ID: <874m3que1i.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH] cpus: make qemu_mutex_iothread_locked() understand co-routines List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Paolo Bonzini , qemu-devel@nongnu.org, Peter Crosthwaite , Richard Henderson Stefan Hajnoczi writes: > On Tue, Nov 01, 2016 at 04:21:36PM +0000, Alex Bennée wrote: >> >> Paolo Bonzini writes: >> >> > On 21/10/2016 13:54, Alex Bennée wrote: >> >> There is a slight wart when checking for the state of the BQL when using >> >> GThread base co-routines (which we keep for ThreadSanitizer runs). While >> >> the main-loop holds the BQL it is suspended until the co-routine >> >> completes however the co-routines run in a separate thread so checking >> >> the TLS variable could be wrong. >> >> >> >> We fix this by expanding the check to include qemu_in_coroutine() for >> >> GThread based builds. As it is not used for production builds I'm not >> >> overly worried about any performance impact which should be negligible >> >> anyway. >> >> >> >> Signed-off-by: Alex Bennée >> >> Cc: Stefan Hajnoczi >> > >> > This is wrong unfortunately. It is possible to run coroutines outside >> > the BQL (e.g. with -device virtio-blk,iothread=foo). >> > >> > Do you know exactly why TSAN has no love for coroutines? >> >> The current production stuff is due to missing support for new stacks >> with setcontext. However I have built the latest tsan support library >> and that seems happy without the gthread co-routines. >> >> Currently I'm dealing with glib's racy gthread support however. > > I think Paolo suggested we drop the GThread backend on IRC. I agree > that we should do that since GThread co-routines break code that uses > thread-local variables and have never truly worked. Indeed I have pulled your patch into my current series of sanitizer fixes. Once I can fix the setcontext/sigjmp confusion for a __SANITIZER__ builds I'll post the series. -- Alex Bennée