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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 17/08/2023 15:46, James Clark wrote:
> 
> 
> On 17/08/2023 15:39, Suzuki K Poulose wrote:
>> 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.
>>
>> Thanks for the report. But please see below:
>>
>>>
>>> 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;
>>
>> This looks wrong. The devlist should be only released on the "driver"
>> unload, not on every device release. The list retains the fwnode to
>> assign the same name for a device, if it is re-probed (e.g., due to
>> -EPROBE_DEFER error).
>>
>> Suzuki
>>
> 
> I think in that case my suggestion to change it to devm_krealloc_array
> might be wrong then. Probably worth putting an explicit comment there in
> case someone tries to tidy up all the non devm allocators to devm ones.
> 
> But how do you release a single device without releasing the whole driver?

You could unbind a device from the driver and that will make another 
driver probe it. I know it works for PCI/platform with VFIO.

Suzuki

> 
> James