Dear Andrew,
On Tue, Aug 11, 2020 at 01:49:09PM -0700, Andrew Morton wrote:
> On Tue, 11 Aug 2020 14:46:56 +0200 Eugeniu Rosca <erosca@xxxxxxxxxxxxxx> 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@xxxxxxxxxx/
> >
> > ...
> >
> > --- 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?
Thank you for the prompt feedback.
The issue popped up as a result of static analysis and code review.
Therefore, I lack any specific runtime behavior example being fixed.
Nevertheless, I think this does not diminish the concern expressed in
the description of the patch.
--
Best regards,
Eugeniu Rosca
