[PATCH] dmaengine: dmatest: bug out when dma test times out

[Adam Wallis]

On 11/2/2017 4:17 AM, Vinod Koul wrote:
> On Wed, Nov 01, 2017 at 03:49:57PM -0400, Adam Wallis wrote:
>> Commit adfa543e7314 ("dmatest: don't use set_freezable_with_signal()")
>> introduced a bug (that is in fact documented by the patch commit text)
>> that leaves behind a dangling pointer. Since the done_wait structure is
>> allocated on the stack, future invocations to the DMATEST can produce
>> undesirable results (e.g., corrupted spinlocks). Ideally, this would be
>> cleaned up in the the thread handler, but at the very least, the kernel
>> is left in a very precarious scenario that can lead to some long debug
>> sessions when the crash comes later.
>>
>> This bug has also been captured at
>> https://bugzilla.kernel.org/show_bug.cgi?id=197605
>>
>> Signed-off-by: Adam Wallis <awallis at codeaurora.org>
>> ---
>>  drivers/dma/dmatest.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
>> index 34ff532..95c662f 100644
>> --- a/drivers/dma/dmatest.c
>> +++ b/drivers/dma/dmatest.c
>> @@ -706,7 +706,7 @@ static int dmatest_func(void *data)
>>  			result("test timed out", total_tests, src_off, dst_off,
>>  			       len, 0);
>>  			failed_tests++;
>> -			continue;
>> +			BUG();
> 
> This will essentially kill the system. People have been trying to remove
> usage of BUG(), we should not do that. Complaining violently makes sense..
> 
Understood. In my testing, the system is effectively shot if you run the dmatest
in a tight enough loop, however, at least using a WARN would alert the user that
the kernel might be in an unstable state. I will submit another patch with a
WARN, even though, I hope a proper fix can be introduced at some point. I am not
familiar enough with this code to propose such a fix at the moment though.

> 
>>  		} else if (status != DMA_COMPLETE) {
>>  			dmaengine_unmap_put(um);
>>  			result(status == DMA_ERROR ?
>> -- 
>> Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
>> Qualcomm Technologies, Inc. is a member of the
>> Code Aurora Forum, a Linux Foundation Collaborative Project.
>>
> 


-- 
Adam Wallis
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.