linux-kernel - Re: [PATCH] mm: slub: Panic if the object corruption is checked.

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Message-ID: <1495dc28-f16c-4990-ad89-2a90b79a80b8@sk.com>
Date: Tue, 21 Jan 2025 10:48:08 +0900
From: Hyeonggon Yoo <hyeonggon.yoo@...com>
To: Hyesoo Yu <hyesoo.yu@...sung.com>, Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: kernel_team@...ynix.com,
 "janghyuck.kim@...sung.com" <janghyuck.kim@...sung.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Jonathan Corbet <corbet@....net>,
 Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
 David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
 Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <roman.gushchin@...ux.dev>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: slub: Panic if the object corruption is checked.

On 1/21/2025 9:54 AM, Hyesoo Yu wrote:
> On Tue, Jan 21, 2025 at 12:41:01AM +0900, Hyeonggon Yoo wrote:
>> On Mon, Jan 20, 2025 at 5:30 PM Hyesoo Yu <hyesoo.yu@...sung.com> wrote:
>>>
>>> If a slab object is corrupted or an error occurs in its internal
>>> value, continuing after restoration may cause other side effects.
>>> At this point, it is difficult to debug because the problem occurred
>>> in the past. A flag has been added that can cause a panic when there
>>> is a problem with the object.
>>
>> Hi Hyesoo,
>>
>> I'm concerned about this because it goes against the effort to avoid
>> introducing new BUG() calls [1].
>>
>> And I think it would be more appropriate to use existing panic_on_warn
>> functionality [2] which causes
>> a panic on WARN(), rather than introducing a SLUB-specific knob to do
>> the same thing.
>>
>> However SLUB does not call WARN() and uses pr_err() instead when
>> reporting an error.
>> Vlastimil and I talked about changing it to use WARN() a while ago
>> [3], but neither of us
>> have done that yet.
>>
>> Probably you may want to look at it, as it also aligns with your purpose?
>> FYI, if you would like to work on it, please make sure that it WARN()
>> is suppressed during kunit test.
>>
>> [1] https://docs.kernel.org/process/deprecated.html#bug-and-bug-on
>> [2] https://www.kernel.org/doc/html/v6.9/admin-guide/sysctl/kernel.html#panic-on-warn
>> [3] https://lore.kernel.org/linux-mm/d4219cd9-32d3-4697-93b9-6a44bf77d50c@suse.cz
>>
>> Best,
>> Hyeonggon
> 
> Thanks for response.
> 
> Using warn() instead of panic, is a great idea.
> Thanks for pointing out what I missed.

Just for clarification, I think changing the common error reporting
logic (like, slab_bug()) to use WARN() will be preferable to inserting
new WARN()s at random points, which is what this patch does now.

Best,
Hyeonggon