Re: [PATCH v3 2/8] coresight: configfs: Don't assume active until cscfg_mgr is set

[Leo Yan <leo.yan@arm.com>]

On Tue, Jul 28, 2026 at 04:00:14PM +0100, James Clark wrote:
> Perf's etm_setup_aux() calls cscfg_activate_config() and dereferences
> cscfg_mgr, which can be done after coresight_init() has initialized the
> Perf PMU but before cscfg_init() has finished while the driver is still
> loading.

For this patch, if Perf PMU is dependent on cscfg, why we cannot
adjust the init sequence that first call cscfg_init(), then register
cs_etm PMU event?

In _cscfg_activate_config(), I can see it dereferences cscfg_mgr:

  if (cscfg_mgr->load_state == CSCFG_UNLOAD)

This patch does not check if cscfg_mgr is set. If we try to check
cscfg_mgr every time before dereferences it, this approach is quite
fragile.


> Fix it by only assuming cscfg is initialized if cscfg_mgr is set.
> 
> Reported-by: sashiko-bot <sashiko-bot@kernel.org>
> Fixes: a0114b4740dd ("coresight: etm-perf: Update to activate selected configuration")
> Signed-off-by: James Clark <james.clark@linaro.org>
> ---
>  drivers/hwtracing/coresight/coresight-syscfg.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index 2bfdd7b45e49..475e8fefa100 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -581,7 +581,7 @@ int cscfg_load_config_sets(struct cscfg_config_desc **config_descs,
>  	int err = 0;
>  
>  	mutex_lock(&cscfg_mutex);
> -	if (cscfg_mgr->load_state != CSCFG_NONE) {
> +	if (!cscfg_mgr || cscfg_mgr->load_state != CSCFG_NONE) {
>  		mutex_unlock(&cscfg_mutex);
>  		return -EBUSY;

If cscfg_mgr is NULL, would directly bail out? This can avoid adding
check for every dereference.

Thanks,
Leo

P.S. For me, this kind of rare race condition reported by Sashiko can
sometimes distract from the main issue. Trying to address it in the
same series may mix different issues together. I miss the simpler
approach where issues could be resolved with clear boundary.