Re: [PATCH 2/2] coresight: core: fix memory leak in dict->fwnode_list

[James Clark <james.clark@arm.com>]

On 17/08/2023 09:59, Junhao He wrote:
> There are memory leaks reported by kmemleak:
> ...
> unreferenced object 0xffff2020103c3200 (size 256):
>   comm "insmod", pid 4476, jiffies 4294978252 (age 50072.536s)
>   hex dump (first 32 bytes):
>     10 60 40 06 28 20 ff ff 10 c0 59 06 20 20 ff ff  .`@.( ....Y.  ..
>     10 e0 47 06 28 20 ff ff 10 00 49 06 28 20 ff ff  ..G.( ....I.( ..
>   backtrace:
>     [<0000000034ec4724>] __kmem_cache_alloc_node+0x2f8/0x348
>     [<0000000057fbc15d>] __kmalloc_node_track_caller+0x5c/0x110
>     [<00000055d5e34b>] krealloc+0x8c/0x178
>     [<00000000a4635beb>] coresight_alloc_device_name+0x128/0x188 [coresight]
>     [<00000000a92ddfee>] funnel_cs_ops+0x10/0xfffffffffffedaa0 [coresight_funnel]
>     [<00000000449e20f8>] dynamic_funnel_ids+0x80/0xfffffffffffed840 [coresight_funnel]
> ...
> 
> when remove driver, the golab variables defined by the macro
> DEFINE_CORESIGHT_DEVLIST will be released, dict->nr_idx and
> dict->fwnode_list are cleared to 0. The lifetime of the golab
> variable has ended. So the buffer pointer is lost.
> 
> Use the callback of devm_add_action_or_reset() to free memory.
> 
> Fixes: 0f5f9b6ba9e1 ("coresight: Use platform agnostic names")
> Signed-off-by: Junhao He <hejunhao3@huawei.com>
> ---
>  drivers/hwtracing/coresight/coresight-core.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 9fabe00a40d6..6849faad697d 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1756,6 +1756,20 @@ bool coresight_loses_context_with_cpu(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(coresight_loses_context_with_cpu);
>  
> +void coresight_release_dev_list(void *data)
> +{
> +	struct coresight_dev_list *dict = data;
> +
> +	mutex_lock(&coresight_mutex);
> +
> +	if (dict->nr_idx) {
> +		kfree(dict->fwnode_list);
> +		dict->nr_idx = 0;
> +	}
> +
> +	mutex_unlock(&coresight_mutex);
> +}
> +
>  /*
>   * coresight_alloc_device_name - Get an index for a given device in the
>   * device index list specific to a driver. An index is allocated for a
> @@ -1766,12 +1780,16 @@ EXPORT_SYMBOL_GPL(coresight_loses_context_with_cpu);
>  char *coresight_alloc_device_name(struct coresight_dev_list *dict,
>  				  struct device *dev)
>  {
> -	int idx;
> +	int idx, ret;
>  	char *name = NULL;
>  	struct fwnode_handle **list;
>  
>  	mutex_lock(&coresight_mutex);
>  
> +	ret = devm_add_action_or_reset(dev, coresight_release_dev_list, dict);
> +	if (ret)
> +		goto done;
> +

Hi Junhao,

Changing the list allocator to a devm one fixes the issue without having
to add the callback:

  -               list = krealloc_array(dict->fwnode_list,
  +               list = devm_krealloc_array(dev, dict->fwnode_list,

The callback stands out a bit and would make someone reading it wonder
why only that one is done that way but all other allocations in
Coresight avoid it.

The nr_idx variable doesn't need to be zeroed because its backed by a
static variable and is zeroed when the module is reloaded as far as I
can see.

Thanks
James

>  	idx = coresight_search_device_idx(dict, dev_fwnode(dev));
>  	if (idx < 0) {
>  		/* Make space for the new entry */

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