On 06/07/2013 04:34 PM, Mark Brown wrote:
On Fri, Jun 07, 2013 at 07:57:29PM +0800, Qiao Zhou wrote:
the dmaengine_pcm_dma_complete callback is usually executed after the dma interrupt, which uses tasklet_schedule, workqueue, or other method for quick int handler return.
in some corner case, where pcm stream is released unexpected, like media server is killed, the runtime parameter will be freed. if it happens between the t1 and t2 in below chart, then the callback will try to access members of paramters which is already freed, and kernel panics.
to avoid this issue, add runtime checking before other handling in dmaengine_pcm_dma_complete. if pcm stream is already released, just ignore the current handling and return.
This doesn't seem like a good or robust way of fixing this, if we're tearing down the resources the DMA is using while the DMA is in progress then in the worst case that might include the memory being DMAed and of course there's races if you just check the pointer - the pointer can be checked at the same time as it's being freed (or between the free and the clear).
I think we should be either halting the DMA or waiting for it to finish here.
I haven't see the original patch, but the proper solution to this problem should be to add a check to snd_dmaengine_pcm_close() to see if the DMA is still running, and if it is call dmaengine_terminate_all() for the DMA channel associated with the PCM. Everything else will probably still be racy.
- Lars