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[79.241.252.131]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3cbf1f5fc1bsm6731329f8f.54.2025.08.27.13.01.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 13:01:46 -0700 (PDT) Message-ID: <0de24b30-70ad-498f-9eac-01596c8713df@redhat.com> Date: Wed, 27 Aug 2025 22:01:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] huge_mm.h: disallow is_huge_zero_folio(NULL) 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> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E6A991A0014 X-Rspam-User: X-Stat-Signature: 3ia4t3eh15hxtsmqfibxrn9w3afo4qn7 X-Rspamd-Server: rspam09 X-HE-Tag: 1756324910-492005 X-HE-Meta: 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 DNx6EKU3 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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: > 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. > > I've had this kind of thing happen several times before. > >> #include >> >> #include /* only for vma_is_dax() */ >> @@ -479,6 +480,8 @@ extern unsigned long huge_zero_pfn; >> >> static inline bool is_huge_zero_folio(const struct folio *folio) >> { >> + VM_WARN_ON_ONCE(folio == NULL); >> + > > Convention is VM_WARN_ON_ONCE(!folio); Wanted to comment the same thing. -- Cheers David / dhildenb