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

[Dongli Zhang <dongli.zhang@oracle.com>]

On 8/11/20 5:46 AM, Eugeniu Rosca 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/
> 
> Fixes: 52f23478081ae0 ("mm/slub.c: fix corrupted freechain in deactivate_slab()")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dongli Zhang <dongli.zhang@oracle.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> ---
>  mm/slub.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 68c02b2eecd9..9a3e963b02a3 100644
> --- 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;

This is good to me.

However, this would confuse people when CONFIG_SLUB_DEBUG is not defined.

While reading the source code, people may be curious why to reset freelist when
CONFIG_SLUB_DEBUG is even not defined.

Dongli Zhang