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Subject: Re: [PATCH] mm: cma: fix corruption cma_sysfs_alloc_pages_count
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        gregkh@linuxfoundation.org, surenb@google.com, joaodias@google.com,
        jhubbard@nvidia.com, willy@infradead.org
References: <20210324192044.1505747-1-minchan@kernel.org>
 <18ee5c3e-fba2-0d8d-bd93-5fb8d0dd7a01@gmail.com>
Message-ID: <89ba4c7a-42d2-5412-2367-cc1cffc1117b@gmail.com>
Date:   Wed, 24 Mar 2021 22:49:58 +0300
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24.03.2021 22:43, Dmitry Osipenko пишет:
> 24.03.2021 22:20, Minchan Kim пишет:
>>  static int __init cma_sysfs_init(void)
>>  {
>> -	int i = 0;
>> +	struct kobject *cma_kobj_root;
>> +	struct cma_kobject *cma_kobj;
>>  	struct cma *cma;
>> +	unsigned int i;
> 
>>  	while (--i >= 0) {
> 
> Do you realize that this doesn't work anymore?
> 
>>  		cma = &cma_areas[i];
>> -		kobject_put(&cma->stat->kobj);
>> -	}
>>  
>> -	kfree(cma_stats);
>> -	kobject_put(cma_kobj);
>> +		kobject_put(&cma->cma_kobj->kobj);
>> +		kfree(cma->cma_kobj);
> 
> Freeing a null pointer?
> 
>> +		cma->cma_kobj = NULL;
>> +	}
>> +	kobject_put(cma_kobj_root);
> 

Please try to simulate the errors and check that error path is working
properly in the next version.

Alternatively, we could remove the cma_kobj_release entirely, like Greg
suggested previously, and then don't care about cleaning up at all.