From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 8 Dec 2015 02:33:31 +0000 From: Al Viro To: Andy Lutomirski Cc: Dominique Martinet , "linux-kernel@vger.kernel.org" , V9FS Developers , Linux FS Devel Subject: Re: [V9fs-developer] Hang triggered by udev coldplug, looks like a race Message-ID: <20151208023331.GJ20997@ZenIV.linux.org.uk> References: <20151207224643.GA10531@nautica> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: On Mon, Dec 07, 2015 at 05:59:41PM -0800, Andy Lutomirski wrote: > If I dump all task states (see attached typescript), I see a bunch of > things blocked in 9p rpc. This makes me think it could be a QEMU bug, > not a kernel bug. Maybe, maybe not - I'd suggest dumping the 9p traffic and checking the request and response IDs; at least one bug in that area got fixed (see commit a84b69 for gory details). Really, check if something gets screwed with IDs. They should be unique among outstanding requests and never reused until either a response with the matching ID arrives, *or* TFLUSH on that ID is sent and reply has arrived. If those rules get buggered, it's very easy to get hangs like that.