Re: [PATCH] dmaengine: dmatest: make wait parameter reads interruptible

[Frank Li]

On Sun, Oct 18, 2026 at 07:56:06PM +0200, Karl Mehltretter wrote:
> Reading the wait parameter during a finite test uses wait_event(). The
> reader remains in uninterruptible sleep until all test threads finish.
> Long runs trigger the hung-task detector, and signals cannot stop the
> reader:
>
>   INFO: task cat:71690 blocked for more than 120 seconds.
>   Call trace:
>    dmatest_wait_get+0x17c/0x1d8 [dmatest]
>    param_attr_show+0x6c/0xb0
>
> Use wait_event_interruptible() and propagate the signal error so Ctrl-C
> and timeout can abort the sysfs read. The test threads continue
> independently.
>
> On a Raspberry Pi 500+ RP1 DMA channel, a script configured dmatest with
> 1 MiB buffers and two threads of 2,000 iterations each. The unpatched
> run completed all 4,000 tests without failures in 267 seconds, but
> emitted hung-task reports at 120 and 241 seconds.
>
> With the patch, the same 4,000 tests completed without failures in 269
> seconds and emitted no hung-task report. In a separate patched run,
> SIGTERM terminated the reader. Both test threads continued and completed
> all 200 tests without failures.
>
> Fixes: 2d88ce76eb98 ("dmatest: add a 'wait' parameter")
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

>  drivers/dma/dmatest.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
> index 2ae346939..7e6b6c446 100644
> --- a/drivers/dma/dmatest.c
> +++ b/drivers/dma/dmatest.c
> @@ -287,9 +287,14 @@ static int dmatest_wait_get(char *val, const struct kernel_param *kp)
>  {
>  	struct dmatest_info *info = &test_info;
>  	struct dmatest_params *params = &info->params;
> +	int ret;
>
> -	if (params->iterations)
> -		wait_event(thread_wait, !is_threaded_test_run(info));
> +	if (params->iterations) {
> +		ret = wait_event_interruptible(thread_wait,
> +					       !is_threaded_test_run(info));
> +		if (ret)
> +			return ret;
> +	}
>  	wait = true;
>  	return param_get_bool(val, kp);
>  }
> --
> 2.39.5 (Apple Git-154)
>