From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54746) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a3i9O-0007Jq-0k for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:27:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a3i9N-0005AO-2r for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:27:09 -0500 Date: Tue, 1 Dec 2015 18:26:58 +0800 From: Fam Zheng Message-ID: <20151201102658.GA6787@ad.usersys.redhat.com> References: <1448962590-2842-1-git-send-email-famz@redhat.com> <1448962590-2842-2-git-send-email-famz@redhat.com> <20151201095436.GC6527@noname.str.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151201095436.GC6527@noname.str.redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/3] block: Don't wait serialising for non-COR read requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Jeff Cody , qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi On Tue, 12/01 10:54, Kevin Wolf wrote: > Am 01.12.2015 um 10:36 hat Fam Zheng geschrieben: > > The assertion problem was noticed in 06c3916b35a, but it wasn't > > completely fixed, because even though the req is not marked as > > serialising, it still gets serialised by wait_serialising_requests > > against other serialising requests, which could lead to the same > > assertion failure. > > > > Fix it by even more explicitly skipping the serialising for this > > specific case. > > > > Signed-off-by: Fam Zheng > > And this, my friends, is another example why read/write notifiers are > wrong and should die sooner rather than later. > Yes, I agree, except it's not clear to me what a better alternative solution should be. A immediate question is, with whatever approach we will have, wouldn't we still need to do this sort of "reentrant" COW before the data is overwritten? Fam