From owner-freebsd-current@FreeBSD.ORG Wed Jan 7 00:27:45 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 6CBC716A4CE; Wed, 7 Jan 2004 00:27:45 -0800 (PST) Received: from gw.catspoiler.org (217-ip-163.nccn.net [209.79.217.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id 3D65843D2D; Wed, 7 Jan 2004 00:27:44 -0800 (PST) (envelope-from truckman@FreeBSD.org) Received: from FreeBSD.org (mousie.catspoiler.org [192.168.101.2]) by gw.catspoiler.org (8.12.9p2/8.12.9) with ESMTP id i078RX7E015971; Wed, 7 Jan 2004 00:27:37 -0800 (PST) (envelope-from truckman@FreeBSD.org) Message-Id: <200401070827.i078RX7E015971@gw.catspoiler.org> Date: Wed, 7 Jan 2004 00:27:33 -0800 (PST) From: Don Lewis To: bde@zeta.org.au In-Reply-To: <20040107184629.H7587@gamplex.bde.org> MIME-Version: 1.0 Content-Type: TEXT/plain; charset=us-ascii cc: matk@FreeBSD.org cc: cg@FreeBSD.org cc: current@FreeBSD.org cc: shoesoft@gmx.net Subject: Re: sound/pcm/* bugs (was: Re: page fault panic tracked down (selwakeuppri()) - really sound/pcm/*) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 07 Jan 2004 08:27:45 -0000 On 7 Jan, Bruce Evans wrote: > On Tue, 6 Jan 2004, Don Lewis wrote: > >> [... lots of good stuff] >> I found another bug, though. Holding a mutex across a malloc() call is >> not allowed because malloc() can sleep, and sleeping while holding a >> mutex is not allowed. sndbuf_resize() sndbuf_remalloc() both call >> malloc() to allocate buffers, and sndbuf_alloc() and sndbuf_setup() call >> sndbuf_resize(). The problem is that chn_setblocksize() calls >> sndbuf_remalloc() while the channel mutex is held. We can't just unlock >> the mutex around the sndbuf_remalloc() call because the channel >> interrupt service routine could run while the buffer is being >> re-allocated. It would be best if the channel were to be shut down when >> re-allocating the buffer. This is likely to be messy since >> chn_setblocksize() is called from lots of different places. > > Er, its an M_NOWAIT malloc(), so it can't sleep. M_WAITOK malloc()s > in interrupt handlers would also be bugs, but that is not a problem > here for the same reason. Hmn, I totally missed that. That eliminates the problem of holding the mutex, but probably violates POLA if the sound stops playing because of a transient memory shortage. I also wonder what happens if the buffer goes away while the channel is running, but I'm not curious enough to dive back into the code. > There should be more checks for potential sleeps while holding a mutex. > > Bruce