From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: lguest, Re: -mm merge plans for 2.6.23 From: Rusty Russell In-Reply-To: <20070711.192829.08323972.davem@davemloft.net> References: <20070710013152.ef2cd200.akpm@linux-foundation.org> <20070711122324.GA21714@lst.de> <1184203311.6005.664.camel@localhost.localdomain> <20070711.192829.08323972.davem@davemloft.net> Content-Type: text/plain Date: Thu, 12 Jul 2007 12:48:41 +1000 Message-Id: <1184208521.6005.695.camel@localhost.localdomain> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: David Miller Cc: hch@lst.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Wed, 2007-07-11 at 19:28 -0700, David Miller wrote: > From: Rusty Russell > Date: Thu, 12 Jul 2007 11:21:51 +1000 > > > To do inter-guest (ie. inter-process) I/O you really have to make sure > > the other side doesn't go away. > > You should just let it exit and when it does you receive some kind of > exit notification that resets your virtual device channel. > > I think the reference counting approach is error and deadlock prone. > Be more loose and let the events reset the virtual devices when > guests go splat. There are two places where we grab task refcnt. One might be avoidable (will test and get back) but the deferred wakeup isn't really: /* We cache one process to wakeup: helps for batching & wakes outside locks. */ void set_wakeup_process(struct lguest *lg, struct task_struct *p) { if (p == lg->wake) return; if (lg->wake) { wake_up_process(lg->wake); put_task_struct(lg->wake); } lg->wake = p; if (lg->wake) get_task_struct(lg->wake); } We drop the lock after I/O, and then do this wakeup. Meanwhile the other task might have exited. I could get rid of it, but I don't think there's anything wrong with the code... Cheers, Rusty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org