Re: [PATCH] mm: slub: fix conversion of freelist_corrupted()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 11 Aug 2020 14:46:56 +0200 Eugeniu Rosca <erosca@de.adit-jv.com> wrote:

> Commit 52f23478081ae0 ("mm/slub.c: fix corrupted freechain in
> deactivate_slab()") suffered an update when picked up from LKML [1].
> 
> Specifically, relocating 'freelist = NULL' into 'freelist_corrupted()'
> created a no-op statement. Fix it by sticking to the behavior intended
> in the original patch [1]. Prefer the lowest-line-count solution.
> 
> [1] https://lore.kernel.org/linux-mm/20200331031450.12182-1-dongli.zhang@oracle.com/
> 
> ...
>
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -677,7 +677,6 @@ static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
>  	if ((s->flags & SLAB_CONSISTENCY_CHECKS) &&
>  	    !check_valid_pointer(s, page, nextfree)) {
>  		object_err(s, page, freelist, "Freechain corrupt");
> -		freelist = NULL;
>  		slab_fix(s, "Isolate corrupted freechain");
>  		return true;
>  	}
> @@ -2184,8 +2183,10 @@ static void deactivate_slab(struct kmem_cache *s, struct page *page,
>  		 * 'freelist' is already corrupted.  So isolate all objects
>  		 * starting at 'freelist'.
>  		 */
> -		if (freelist_corrupted(s, page, freelist, nextfree))
> +		if (freelist_corrupted(s, page, freelist, nextfree)) {
> +			freelist = NULL;
>  			break;
> +		}
>  
>  		do {
>  			prior = page->freelist;

Looks right.

What are the runtime effects of this change?  In other words, what are
the end user visible effects of the present defect?