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

[Hyesoo Yu <hyesoo.yu@samsung.com>]

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On Fri, Feb 21, 2025 at 05:30:59PM +0900, Harry Yoo wrote:
> 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@samsung.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().
> 

Thank you for reviewing the part I missed.
I will remove the WARN in kmem_cache_destory().

Thanks,
Regards.

> >  		}
> >  	}
> >  	spin_unlock_irq(&n->list_lock);
> > -- 
> > 2.28.0
> > 
> 
> -- 
> Cheers,
> Harry
> 

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