linux-kernel - Re: [PATCH v3 2/2] mm: slub: call WARN() when the slab detect an error

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Message-ID: <Z7g5wyjsP1ktucDO@harry>
Date: Fri, 21 Feb 2025 17:30:59 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Hyesoo Yu <hyesoo.yu@...sung.com>
Cc: janghyuck.kim@...sung.com, vbabka@...e.cz,
        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>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] mm: slub: call WARN() when the slab detect an
 error

On Thu, Feb 20, 2025 at 12:39:44PM +0900, Hyesoo Yu 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. It is useful to use WARN() to catch errors at the point
> of issue because WARN() could trigger panic for system debugging when
> panic_on_warn is enabled. WARN() is added where to detect the error
> on slab_err and object_err.
>
> There are cases where slab_err is called before meaningful logs are
> printed. If the WARN() in slab_err cause a panic, these logs will not
> be printed. WARN() should called after these logs are printed. Thus
> slab_err() is splited to __slab_err that calls the WARN() and it is
> called after printing logs.
> 
> Changes in v3:
> - move the WARN from slab_fix to slab_err, object_err to use WARN on
> all error reporting paths.
> 
> Changes in v2:
> - Replace direct calling with BUG_ON with the use of WARN in slab_fix.
> 
> Signed-off-by: Hyesoo Yu <hyesoo.yu@...sung.com>
> Change-Id: I90b2ea9ffc58e3826f7ae9f1a774bb48c2d43bf4
> ---
>  mm/slub.c | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index de62fed12236..7f0583a71cda 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5473,8 +5481,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
>  			remove_partial(n, slab);
>  			list_add(&slab->slab_list, &discard);
>  		} else {
> -			list_slab_objects(s, slab,
> -			  "Objects remaining in %s on __kmem_cache_shutdown()");
> +			list_slab_objects(s, slab);

Could you remove WARN() in kmem_cache_destroy()?

When a cache is destroyed with remaining objects, two WARNINGs being are
printed, one from list_slab_objects() and another from kmem_cache_destroy().
The latter becomes redundant with this patch.

The WARN() is added there because it's good to catch such an error.
At that time, slab_err() and object_err() did not call WARN().

>  		}
>  	}
>  	spin_unlock_irq(&n->list_lock);
> -- 
> 2.28.0
> 

-- 
Cheers,
Harry