Re: [PATCH] Add a slab corruption tracepoint

[Vlastimil Babka <vbabka@suse.cz>]

On 8/8/19 4:11 PM, David Howells wrote:
>     
> Add a tracepoint to log slab corruption messages to the trace log also so
> that it's easier to correlate with other trace messages that are being used
> to track refcounting.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>

Shouldn't that include SLUB? I'm surprised to see SLAB used for
debugging refcounting these days, as the SLUB debugging features are
vastly superior, while SLAB ones are being sometimes found to be broken
for years and removed.

> ---
>  include/trace/events/kmem.h |   23 +++++++++++++++++++++++
>  mm/slab.c                   |    2 ++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index eb57e3037deb..c96f3b03a6e2 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -315,6 +315,29 @@ TRACE_EVENT(mm_page_alloc_extfrag,
>  		__entry->change_ownership)
>  );
>  
> +TRACE_EVENT(slab_corruption,
> +	TP_PROTO(const char *slab, void *object, unsigned int size, unsigned int offset),
> +
> +	TP_ARGS(slab, object, size, offset),
> +
> +	TP_STRUCT__entry(
> +		__field(	void *,		object		)
> +		__field(	unsigned int,	size		)
> +		__field(	unsigned int,	offset		)
> +		__array(	char,		slab, 16	)
> +	),
> +
> +	TP_fast_assign(
> +		strlcpy(__entry->slab, slab, sizeof(__entry->slab));
> +		__entry->object		= object;
> +		__entry->size		= size;
> +		__entry->offset		= offset;
> +	),
> +
> +	TP_printk("slab=%s obj=%px size=%x off=%x",
> +		  __entry->slab, __entry->object, __entry->size, __entry->offset)
> +);
> +
>  #endif /* _TRACE_KMEM_H */
>  
>  /* This part must be outside protection */
> diff --git a/mm/slab.c b/mm/slab.c
> index 9df370558e5d..47c5a86e39be 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1527,6 +1527,8 @@ static void check_poison_obj(struct kmem_cache *cachep, void *objp)
>  				       print_tainted(), cachep->name,
>  				       realobj, size);
>  				print_objinfo(cachep, objp, 0);
> +				trace_slab_corruption(cachep->name, realobj,
> +						      size, i);
>  			}
>  			/* Hexdump the affected line */
>  			i = (i / 16) * 16;
>