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

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Message-ID: <87107f44-b760-5df4-6bcf-8482069a603a@arm.com>
Date:   Thu, 17 Aug 2023 16:01:02 +0100
From:   James Clark <james.clark@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        Junhao He <hejunhao3@...wei.com>, mike.leach@...aro.org,
        leo.yan@...aro.org
Cc:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        jonathan.cameron@...wei.com, yangyicong@...wei.com,
        prime.zeng@...ilicon.com
Subject: Re: [PATCH 2/2] coresight: core: fix memory leak in dict->fwnode_list



On 17/08/2023 15:47, Suzuki K Poulose 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@...wei.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).
> 
> The best way is to free it on module_unload and unfortunately we would
> need to do it from all modules using the DEVLIST.
> 
> Suzuki
> 

Seems like we might also be able to move the separate lists to be one
big list owned by the main 'coresight' module. If all the other modules
are dependent on that one then it's always loaded first and the list is
available. Then it persists as long as the main module is loaded and can
be freed with the normal devm stuff.

That would avoid the awkward combo of the static variables in each
module plus the non devm kalloced list.

> 
>>
>> Suzuki
>>
>