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Thu, 18 Jul 2024 17:36:06 -0700 (PDT) MIME-Version: 1.0 References: <20240717230025.77361-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Fri, 19 Jul 2024 12:35:55 +1200 Message-ID: Subject: Re: [PATCH RFC] mm: warn potential return NULL for kmalloc_array and kvmalloc_array with __GFP_NOFAIL To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, Barry Song , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: A6DE11C001A X-Stat-Signature: kig5e4gds6gs3uyjeyfiufwuospu996m X-HE-Tag: 1721349367-333127 X-HE-Meta: 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 aLQIdb0v 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 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 Thu, Jul 18, 2024 at 8:50=E2=80=AFPM Michal Hocko wrot= e: > > On Thu 18-07-24 20:43:53, Barry Song wrote: > > On Thu, Jul 18, 2024 at 8:32=E2=80=AFPM Michal Hocko = wrote: > > > > > > On Thu 18-07-24 20:18:02, Barry Song wrote: > > > > So the purpose is making sure the semantics - NOFAIL means no failu= re > > > > and we don't need to check ret. If we can't really succeed, it sho= uld throw > > > > a BUG to stop any potential exploits. > > > > > > This would require to panic consistently on failure in all allocator > > > path that can bail out. E.g. page allocator on GFP_NOWAIT|GFP_NOFAIL > > > req. not sure how many more. > > > > Right, this GFP_NOFAIL issue seems quite messy. However, at least vmall= oc > > will retry by itself, even if alloc_pages might have failed with > > GFP_NOWAIT | GFP_NOFAIL. > > > > But isn't that the definition of __GFP_NOFAIL? > > > > * %__GFP_NOFAIL: The VM implementation _must_ retry infinitely: the ca= ller > > * cannot handle allocation failures. The allocation could block > > * indefinitely but will never return with failure. Testing for > > * failure is pointless." > > > > So I believe any code that doesn't retry and ends up returning NULL sho= uld be > > fixed. > > Yes, those shouldn't really fail. NOWAIT|NOFAIL was something that > should never happen and I really hope it doesn't. Others should really > retry but it's been some time since I've checked the last time. I assume allocations directly using alloc_pages() might not respect GFP_NOF= AIL and violate the semantics of GFP_NOFAIL. static inline struct page * __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, struct alloc_context *ac) { /* * Make sure that __GFP_NOFAIL request doesn't leak out and make su= re * we always retry */ if (gfp_mask & __GFP_NOFAIL) { /* * All existing users of the __GFP_NOFAIL are blockable, so= warn * of any new users that actually require GFP_NOWAIT */ if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) goto fail; ... } Additionally, at least drivers/vdpa/vdpa_user/iova_domain.c is incorrect with GFP_ATOMIC | __GFP_NOFAIL. void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain= ) { ... count =3D domain->bounce_size >> PAGE_SHIFT; for (i =3D 0; i < count; i++) { ... /* Copy user page to kernel page if it's in use */ if (map->orig_phys !=3D INVALID_PHYS_ADDR) { page =3D alloc_page(GFP_ATOMIC | __GFP_NOFAIL); memcpy_from_page(page_address(page), map->bounce_page, 0, PAGE_SIZE); } put_page(map->bounce_page); map->bounce_page =3D page; } domain->user_bounce_pages =3D false; out: write_unlock(&domain->bounce_lock); } GFP_NOFAIL things need to be fixed. Let me investigate further. > > These overflow checks were added without any acks by MM people... > -- > Michal Hocko > SUSE Labs Thanks Barry