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

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Message-ID: <c9bef0cd-18a0-ffc0-15c5-3db388275c46@arm.com>
Date:   Thu, 17 Aug 2023 15:46:53 +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 15:39, 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).
> 
> 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?

James