Hello Dongli,
On Thu, Aug 13, 2020 at 11:57:51PM -0700, Dongli Zhang wrote:
> 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@xxxxxxxxxx/
> >
> > Fixes: 52f23478081ae0 ("mm/slub.c: fix corrupted freechain in deactivate_slab()")
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
> > ---
> > 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.
This is a fair point. To address it, the `freelist = NULL` assignment
should be then moved into the body of freelist_corrupted(). If no
concerns on that, I will soon push a v2 implementing this proposal.
--
Best regards,
Eugeniu Rosca
