From: javi.merino@arm.com (Javi Merino) Date: Sun, 11 Dec 2011 17:42:41 +0000 Subject: [PATCH v2] ARM: pl330: Fix a race condition In-Reply-To: References: <4E8C5425.80303@arm.com> <1317892206-3600-1-git-send-email-javi.merino@arm.com> <4EB7B79A.2020004@arm.com> <000c01ccada6$f83f5be0$e8be13a0$%kim@samsung.com> <4ED3B89E.7070903@arm.com> <000e01ccae48$d76a7ba0$863f72e0$%kim@samsung.com> <4ED4AB9A.3060807@arm.com> <03f001ccb4b5$3441f5c0$9cc5e140$%kim@samsung.com> <4EDF3989.3060108@arm.com> <4EDFD278.9090101@arm.com> <4EE1F7F0.70107@arm.com> <4EE20FF1.5070702@arm.com> <4EE220A7.5070101@arm.com> <4EE26670.1060005@arm.com> <4EE4C7B5.2070803@arm.com> Message-ID: <4EE4EB91.6020508@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/12/11 17:10, Jassi Brar wrote: > On 11 December 2011 20:39, Javi Merino wrote: >>>> >>>> What about properly tracking what we have sent to the DMA? Something >>>> like the following (warning *ugly* and untested code ahead, may eat your >>>> kitten): >>>> >>> Yeah, this is like I said 'marker' method. Though we can clean it up a bit. >>> 1) Pack req_running and lstenq together. Make lsteng return invalid value >>> should there be no buff programmed, otherwise 0 or 1. >> >> This can lead to starvation. If lstenq is -1 when the DMA hasn't been >> programmed yet, in _trigger() you don't know which buffer is the >> "oldest", so you may end up always starting the new buffer and >> forgetting about the other one. lstenq as it is right now prevents that. >> > Sorry I don't understand. If lstenq is -1 that means there's no req programmed > so trigger need not do anything. I didn't say we don't need to do anything else. Currently lstenq tracks the last request that pl330_submit_req() has enqueued. I think we should add a req_running (or any other name) that tracks what _trigger() has sent to the DMA. If we pack them together we lose some information and I don't see a way of packing them safely. > Though it's just an idea I haven't implemented and it may not work out. I was trying to implement it and got stuck in _trigger() thinking "ok, so which buffer am I supposed to trigger now..." > Just please give it a try if you can. Thanks. I have a patch that seems to be working. Let me test it a little bit more and I'll send it to the list. Cheers, Javi