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[2003:d8:2f1f:d000:d4e1:a22e:7d95:bb63]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b66c383b1sm42788865e9.3.2025.08.27.13.26.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 13:26:10 -0700 (PDT) Message-ID: <4927ed52-a250-4ae8-b596-6f81020eb31a@redhat.com> Date: Wed, 27 Aug 2025 22:26:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] huge_mm.h: disallow is_huge_zero_folio(NULL) From: David Hildenbrand To: Lorenzo Stoakes , Max Kellermann Cc: akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shikemeng@huaweicloud.com, kasong@tencent.com, nphamcs@gmail.com, bhe@redhat.com, chrisl@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2aa3f478-9c87-4102-b83e-bf235372d834@redhat.com> <20250827150330.280399-1-max.kellermann@ionos.com> <30f52bf5-ff37-4e22-ac57-7be0b03b1f51@lucifer.local> <0de24b30-70ad-498f-9eac-01596c8713df@redhat.com> Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 27.08.25 22:01, David Hildenbrand wrote: > >> This seems not so great. >> >> I really think the VM_WARN_ON_ONCE() should be in folios_put_refs() based >> on what you've said. > > No. > > Everything in folio_put_refs() will dereference the folio and properly > crash the machine when doing something stupid. > > This function, however, will silently swallow a "NULL" pointer. > >> >>> >>> Signed-off-by: Max Kellermann >>> --- >>> include/linux/huge_mm.h | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index 7748489fde1b..bc9ca7798f2e 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -2,6 +2,7 @@ >>> #ifndef _LINUX_HUGE_MM_H >>> #define _LINUX_HUGE_MM_H >>> >>> +#include // for VM_WARN_ON_ONCE() >> >> Please don't do //. >> >> This include is suspect though, huge_mm.h is included from mm.h and thus >> this very easily might break some arch that is weird about this stuff, >> because a ton of stuff includes mm.h including things that might absolutely >> baulk at mmdebug. > > Jup. Very likely this is not required. Took another look and including mmdebug.h should likely be fine, because all it includes is really (1) include/linux/bug.h (2) include/linux/stringify.h But originally, I wonder if we even need mmdebug.h or if it is already implicitly included. huge_mm.h includes mm_types.h (where we already do use VM_WARN...). I assume there we get it implicitly through percpu.h, mmap_lock.h or percpu.h So the include should just get dropped. -- Cheers David / dhildenb