Re: [PATCH] coresight: perf: Fix pointer check with IS_ERR_OR_NULL()

[James Clark <james.clark@linaro.org>]

On 04/09/2025 11:53 am, Leo Yan wrote:
> The returned pointer from .alloc_buffer() callback can be an error, if
> only checking NULL pointer the driver cannot capture errors. The driver
> will proceed even after failure and cause kernel panic.
> 
> Change to use IS_ERR_OR_NULL() check for capture error cases.
> 
> Fixes: 0bcbf2e30ff2 ("coresight: etm-perf: new PMU driver for ETM tracers")
> Reported-by: Tamas Zsoldos <tamas.zsoldos@arm.com>
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm-perf.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index f677c08233ba1a28b277674662c6e6db904873dd..440d967f5d0962df187a81b0dd69a7d82a8b62ba 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -198,7 +198,7 @@ static void free_sink_buffer(struct etm_event_data *event_data)
>   	cpumask_t *mask = &event_data->mask;
>   	struct coresight_device *sink;
>   
> -	if (!event_data->snk_config)
> +	if (IS_ERR_OR_NULL(event_data->snk_config))
>   		return;
>   
>   	if (WARN_ON(cpumask_empty(mask)))
> @@ -450,7 +450,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
>   	event_data->snk_config =
>   			sink_ops(sink)->alloc_buffer(sink, event, pages,
>   						     nr_pages, overwrite);
> -	if (!event_data->snk_config)
> +	if (IS_ERR_OR_NULL(event_data->snk_config))
>   		goto err;

I think the bug is in TRBE. It's the only one that returns an error 
pointer, but only for -ENOMEM which would normally be NULL for alloc 
type functions anyway.

Also it's assigned to event_data->snk_config which is later NULL checked 
rather than IS_ERR_OR_NULL in free_sink_buffer(). Maybe that path 
doesn't happen, but all instances should be updated anyway.

It's much easier to keep it as NULL and make the fix in TRBE. It also 
wouldn't need to be backported as far.

>   
>   out:
> 
> ---
> base-commit: fa71e9cb4cfa59abb196229667ec84929bdc18fe
> change-id: 20250904-cs_etm_auxsetup_fix_error_handling-cb7e07ed9adf
> 
> Best regards,