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Fri, 26 Sep 2025 08:38:50 -0700 (PDT) MIME-Version: 1.0 References: <202509171214.912d5ac-lkp@intel.com> <7a3406c6-93da-42ee-a215-96ac0213fd4a@suse.cz> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 26 Sep 2025 08:38:39 -0700 X-Gm-Features: AS18NWDgSteTnQAeHe58pnPN5CXO_C6LUnKFpTmB_8Hvkh2DQsaUFE0c0GhVrg0 Message-ID: Subject: Re: [linux-next:master] [slab] db93cdd664: BUG:kernel_NULL_pointer_dereference,address To: Alexei Starovoitov Cc: Vlastimil Babka , kernel test robot , Alexei Starovoitov , Harry Yoo , oe-lkp@lists.linux.dev, kbuild test robot , kasan-dev , "open list:CONTROL GROUP (CGROUP)" , linux-mm Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 98384C000E X-Stat-Signature: jok97tpn89665xwk91njfmugr3fy8hep X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758901132-750341 X-HE-Meta: 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 maSTfx0b lPFw/B0Bsj77qhyReUtp48jKHHHpW9LGPiK8JcVEDuztfjrjPblotWtOet0ctPA/I3Zt1HDj1VpzorX+FhvKYgszjnBfkOR3dWRDSltySk6zz7PUTqE/inubARWQkrR3mXdks20/aAkWSuNOlOaPszhQMc15fROXsokjTXBVm6vf6DjPk8N2++QyHUD/bAvTN9JZLZ9oTrswShvk7FBT1pgO4e4M8nEVv5U6VxI3vl5k8109EnqIvq3BYLKHsDi4TQhDS7QqSrJoeZBkeFMMyXtDYv9KEqsJ39G2XBKfKfEno2ZtnAJYcGoW7f9+obOnyfEiZMgvLC9yKzwSvCAwNUIcK3i3LeS7DDd5Lqq2QeRlX7pM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 26, 2025 at 8:30=E2=80=AFAM Alexei Starovoitov wrote: > > On Fri, Sep 26, 2025 at 1:25=E2=80=AFPM Vlastimil Babka = wrote: > > > > On 9/19/25 20:31, Alexei Starovoitov wrote: > > > On Fri, Sep 19, 2025 at 8:01=E2=80=AFAM Suren Baghdasaryan wrote: > > >> > > >> > > > >> > I would not. I think adding 'boot or not' logic to these two > > >> > will muddy the waters and will make the whole slab/page_alloc/memc= g > > >> > logic and dependencies between them much harder to follow. > > >> > I'd either add a comment to alloc_slab_obj_exts() explaining > > >> > what may happen or add 'boot or not' check only there. > > >> > imo this is a niche, rare and special. > > >> > > >> Ok, comment it is then. > > >> Will you be sending a new version or Vlastimil will be including tha= t > > >> in his fixup? > > > > > > Whichever way. I can, but so far Vlastimil phrasing of comments > > > were much better than mine :) So I think he can fold what he prefers. > > > > I'm adding this. Hopefully we'll be able to make sheaves the only percp= u > > caching layer in SLUB in the (near) future, and then requirement for > > cmpxchg16b for allocations will be gone. > > > > diff --git a/mm/slub.c b/mm/slub.c > > index 9f1054f0b9ca..f9f7f3942074 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -2089,6 +2089,13 @@ int alloc_slab_obj_exts(struct slab *slab, struc= t kmem_cache *s, > > gfp &=3D ~OBJCGS_CLEAR_MASK; > > /* Prevent recursive extension vector allocation */ > > gfp |=3D __GFP_NO_OBJ_EXT; > > + > > + /* > > + * Note that allow_spin may be false during early boot and its > > + * restricted GFP_BOOT_MASK. Due to kmalloc_nolock() only suppo= rting > > + * architectures with cmpxchg16b, early obj_exts will be missin= g for > > + * very early allocations on those. > > + */ > > lgtm. Maybe add a sentence about future sheaves plan, so it's clear > that there is a path forward and above won't stay forever. LGTM as well. Thanks!