From: peter.ujfalusi@ti•com (Peter Ujfalusi)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2] dmaengine: edma: Implement device_synchronize callback
Date: Thu, 11 Feb 2016 13:12:20 +0200 [thread overview]
Message-ID: <56BC6C94.1060409@ti.com> (raw)
In-Reply-To: <56BC5759.80000@metafoo.de>
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 <peter.ujfalusi@ti•com>
>
> 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
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next prev parent reply other threads:[~2016-02-11 11:12 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-11 9:08 [PATCH v2] dmaengine: edma: Implement device_synchronize callback Peter Ujfalusi
2016-02-11 9:41 ` Lars-Peter Clausen
2016-02-11 11:12 ` Peter Ujfalusi [this message]
2016-02-11 12:13 ` Lars-Peter Clausen
2016-02-22 2:51 ` Vinod Koul
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