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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 18 Jun 2021 16:15:11 +0300
Message-ID: <CAHp75VePzuYwHxA4S8UiUKG1uSqpvnJhfajjJkQi1qS-BhHSdg@mail.gmail.com>
Subject: Re: [PATCH v1] mm: slub: fix the leak of alloc/free traces debugfs interface
To:     Faiyaz Mohammed <faiyazm@codeaurora.org>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        linux-mm <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg KH <greg@kroah.com>, glittao@gmail.com,
        vinmenon@codeaurora.org, Catalin Marinas <catalin.marinas@arm.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>
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On Fri, Jun 18, 2021 at 3:38 PM Faiyaz Mohammed <faiyazm@codeaurora.org> wrote:
>
> fix the leak of alloc/free traces debugfs interface, reported

Fix

> 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?

> 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@codeaurora.org>

...

>  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)

>  }

-- 
With Best Regards,
Andy Shevchenko