From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter.ujfalusi@ti.com (Peter Ujfalusi) Date: Thu, 11 Feb 2016 13:12:20 +0200 Subject: [PATCH v2] dmaengine: edma: Implement device_synchronize callback In-Reply-To: <56BC5759.80000@metafoo.de> References: <1455181722-32099-1-git-send-email-peter.ujfalusi@ti.com> <56BC5759.80000@metafoo.de> Message-ID: <56BC6C94.1060409@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 02/11/2016 11:41 AM, Lars-Peter Clausen wrote: > On 02/11/2016 10:08 AM, Peter Ujfalusi wrote: >> We need the callback to support the dmaengine_terminate_sync(). >> >> Signed-off-by: Peter Ujfalusi > > Looks good, but I noticed a slight race condition in > edma_completion_handler(). You need to fetch echan->desc while holding the > vchan.lock. Otherwise this can race against terminate_all() and the callback > might get scheduled even though terminate_all() completed and then there is > a race where the synchronize() operation could be called before the callback > gets scheduled, which means it doesn't do its intended job. Highly unlikely > to happen, but theoretically possible. Right, actually I had (have) another series fixing the very same race in a different way - patching the terminate_all (series attached). We have seen race with RT kernel on uniprocessor setup. The tasklet_kill after the terminate_all will execute the scheduled task unconditionally, so the vchan_complete() will run after we have terminated the channel, which might be not what we want. I have also seen a race condition as explained in the first patch. The only way I was able to fix that by using the attached patches. Unfortunately I can not test RT with mainline yet, so I'm not 100% sure if by using the dmaengine_terminate_sync() in drivers will fix the issue. -- P?ter -------------- next part -------------- A non-text attachment was scrubbed... Name: 0001-dmaengine-virt-dma-Support-for-ignoring-callback-aft.patch Type: text/x-patch Size: 4081 bytes Desc: not available URL: -------------- next part -------------- A non-text attachment was scrubbed... Name: 0002-dmaengine-omap-dma-Prevent-race-between-vchan_comple.patch Type: text/x-patch Size: 1215 bytes Desc: not available URL: -------------- next part -------------- A non-text attachment was scrubbed... Name: 0003-dmaengine-edma-Prevent-race-between-vchan_complete-a.patch Type: text/x-patch Size: 1230 bytes Desc: not available URL: