linux-kernel - Re: [PATCH] xfs: use kmem_cache_free() for kmem

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Message-ID: <9db5d16a-2999-07a4-c49d-7417601f834f@suse.cz>
Date:   Tue, 12 Oct 2021 23:32:25 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Darrick J. Wong" <djwong@...nel.org>,
        David Rientjes <rientjes@...gle.com>
Cc:     Rustam Kovhaev <rkovhaev@...il.com>,
        Dave Chinner <david@...morbit.com>, linux-xfs@...r.kernel.org,
        cl@...ux.com, penberg@...nel.org, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, gregkh@...uxfoundation.org,
        Al Viro <viro@...iv.linux.org.uk>, dvyukov@...gle.com
Subject: Re: [PATCH] xfs: use kmem_cache_free() for kmem_cache objects

On 10/12/2021 10:43 PM, Darrick J. Wong wrote:
> On Tue, Oct 12, 2021 at 01:43:20PM -0700, Darrick J. Wong wrote:
>> On Sun, Oct 03, 2021 at 06:07:20PM -0700, David Rientjes wrote:
>>> On Thu, 30 Sep 2021, Rustam Kovhaev wrote:
>>>
>>>>>>> I think it's fair if something like XFS (not meant for tiny systems AFAIK?)
>>>>>>> excludes SLOB (meant for tiny systems). Clearly nobody tried to use these
>>>>>>> two together last 5 years anyway.
>>>>>>
>>>>>> +1 for adding Kconfig option, it seems like some things are not meant to
>>>>>> be together.
>>>>>
>>>>> But if we patch SLOB, we won't need it.
>>>>
>>>> OK, so we consider XFS on SLOB a supported configuration that might be
>>>> used and should be tested.
>>>> I'll look into maybe adding a config with CONFIG_SLOB and CONFIG_XFS_FS
>>>> to syzbot.
>>>>
>>>> It seems that we need to patch SLOB anyway, because any other code can
>>>> hit the very same issue.
>>>>
>>>
>>> It's probably best to introduce both (SLOB fix and Kconfig change for 
>>> XFS), at least in the interim because the combo of XFS and SLOB could be 
>>> broken in other ways.  If syzbot doesn't complain with a patched kernel to 
>>> allow SLOB to be used with XFS, then we could potentially allow them to be 
>>> used together.
>>>
>>> (I'm not sure that this freeing issue is the *only* thing that is broken, 
>>> nor that we have sufficient information to make that determination right 
>>> now..)
>>
>> I audited the entire xfs (kernel) codebase and didn't find any other
>> usage errors.  Thanks for the patch; I'll apply it to for-next.

Which patch, the one that started this thread and uses kmem_cache_free() instead
of kfree()? I thought we said it's not the best way?

> Also, the obligatory
> 
> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> 
> --D
> 
>>
>> --D