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b=c0X1iM/loYQV+lM9Y7nboPQ5AI057tcs4b3NzAj+4Ek9Mgu7fDkzUIT4bbM9KSX2G XVawRbC0AKM05vBRWJMZWLNgk2qDYdhQdB5GpVQBGYgZpWu66sjDgz6f9RrRnbqgWJ m6ays8iGIBJ6yqow4uNHPsK5Lix/zhsvs7/q/qc8015Ki9N9YyYJvj0b7V6NOr0qoY s3r1xNWSe24u7FGHpMdykAN7BkR8hh/cp8OsqbQTRE7zVd9kToPNuXO6Tgo+OurmpY 2ZFjTof4Gzk32YdqX13IeddI/nNkWhEVd0oKNBs9/95fiT5m/8uBmxrRoQWk1jpgq9 U7ZE/jfalFfIg== Message-ID: Date: Wed, 15 Apr 2026 12:35:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 07/16] arm64/mm: Convert READ_ONCE() as p4dp_get() while accessing P4D To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com References: <20260224051153.3150613-1-anshuman.khandual@arm.com> <20260224051153.3150613-8-anshuman.khandual@arm.com> <238ab437-06b1-43ef-86bb-9341c02040b1@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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>>> + >>> + BUG_ON(!pgtable_l4_enabled()); >> >> Heh, while at it, convert that to a VM_WARN_ON_ONCE() or anything else >> that is not a BUG. >> >> I strongly assume CONFIG_DEBUG_VM checks are sufficient. > > There are multiple similar BUG_ON() instances > > arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l4_enabled()); > arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l5_enabled()); > > arch/arm64/mm/mmu.c: BUG_ON(pmd_val(old_pmd) != 0 && > arch/arm64/mm/mmu.c: BUG_ON(pud_val(old_pud) != 0 && > arch/arm64/mm/mmu.c: BUG_ON(p4d_val(old_p4d) != 0 && > > Shall we convert all of them as VM_WARN_ON_ONCE() in a separate patch > as a pre-requisite ? In MM at least, we fix them up when touching the code, and only sometimes convert entire files. As documented in Documentation/process/coding-style.rst, there might be some exceptions where BUG_ON makes sense (severe data corruption possible), and some cases would want to use WARN_ON_ONCE() + recovery code. All of these cases here sound like VM_WARN_ON_ONCE() is more than sufficient though, so feel free to convert them all in one shot. -- Cheers, David