linux-kernel - Re: [PATCH v1] mm: slub: fix the leak of alloc/free traces debugfs interface

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Date:   Sun, 20 Jun 2021 21:31:28 +0530
From:   Faiyaz Mohammed <faiyazm@...eaurora.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg KH <greg@...ah.com>, glittao@...il.com,
        vinmenon@...eaurora.org, Catalin Marinas <catalin.marinas@....com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v1] mm: slub: fix the leak of alloc/free traces debugfs
 interface



On 6/18/2021 6:45 PM, Andy Shevchenko wrote:
> On Fri, Jun 18, 2021 at 3:38 PM Faiyaz Mohammed <faiyazm@...eaurora.org> wrote:
>>
>> fix the leak of alloc/free traces debugfs interface, reported
> 
> Fix
> 
Okay, I will update in next patch version.

>> by kmemleak like below,
>>
>> unreferenced object 0xffff00091ae1b540 (size 64):
>>   comm "lsbug", pid 1607, jiffies 4294958291 (age 1476.340s)
>>   hex dump (first 32 bytes):
>>     02 00 00 00 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b  ........kkkkkkkk
>>     6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
>>   backtrace:
>>     [<ffff8000106b06b8>] slab_post_alloc_hook+0xa0/0x418
>>     [<ffff8000106b5c7c>] kmem_cache_alloc_trace+0x1e4/0x378
>>     [<ffff8000106b5e40>] slab_debugfs_start+0x30/0x50
>>     slab_debugfs_start at mm/slub.c:5831
>>     [<ffff8000107b3dbc>] seq_read_iter+0x214/0xd50
>>     [<ffff8000107b4b84>] seq_read+0x28c/0x418
>>     [<ffff8000109560b4>] full_proxy_read+0xdc/0x148
>>     [<ffff800010738f24>] vfs_read+0x104/0x340
>>     [<ffff800010739ee0>] ksys_read+0xf8/0x1e0
>>     [<ffff80001073a03c>] __arm64_sys_read+0x74/0xa8
>>     [<ffff8000100358d4>] invoke_syscall.constprop.0+0xdc/0x1d8
>>     [<ffff800010035ab4>] do_el0_svc+0xe4/0x298
>>     [<ffff800011138528>] el0_svc+0x20/0x30
>>     [<ffff800011138b08>] el0t_64_sync_handler+0xb0/0xb8
>>     [<ffff80001001259c>] el0t_64_sync+0x178/0x17c
> 
> Can you shrink this a bit?
>
Okay

>> Fixes: 84a2bdb1b458fc968d6d9e07dab388dc679bd747 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
> 
> We use 12, which is shorter.
> 
>> Link: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/mm/slub.c?h=next-20210617&id=84a2bdb1b458fc968d6d9e07dab388dc679bd747
> 
>>
> 
> Must be no blank lines in the tag block.
> >> Signed-off-by: Faiyaz Mohammed <faiyazm@...eaurora.org>
> 
Okay
> ...
> 
>>  static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
>>  {
>> -       loff_t *spos = v;
>>         struct loc_track *t = seq->private;
>>
>> +       v = ppos;
>>         if (*ppos < t->count) {
>> -               *ppos = ++*spos;
>> -               return spos;
>> +               ++*ppos;
>> +               return v;
>>         }
>> -       *ppos = ++*spos;
>> +       ++*ppos;
>>         return NULL;
> 
> Can it be
> 
>        v = ppos;
>        ++*ppos;
>        if (*ppos <= t->count>               return v;
>        return NULL;
> 
> ?  (basically the question is, is the comparison equivalent in this case or not)
> 
>>  }
>Yes, we can update it and slab_debugfs_show has the index check as well.
I will update in next patch version.

Thanks and regards,
Mohammed Faiyaz