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([2a09:80c0:192:0:20af:34be:985b:b6c8]) by smtp.gmail.com with ESMTPSA id q3-20020a05600000c300b00225285b8136sm18377611wrx.38.2022.08.25.00.10.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Aug 2022 00:10:42 -0700 (PDT) Message-ID: <50703dda-bbee-7484-97ff-87d6ea75bf80@redhat.com> Date: Thu, 25 Aug 2022 09:10:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v2 1/5] mm/hugetlb: fix races when looking up a CONT-PTE size hugetlb page Content-Language: en-US To: Baolin Wang , Mike Kravetz Cc: akpm@linux-foundation.org, songmuchun@bytedance.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <0e5d92da043d147a867f634b17acbcc97a7f0e64.1661240170.git.baolin.wang@linux.alibaba.com> <4c24b891-04ce-2608-79d2-a75dc236533f@redhat.com> <376d2e0a-d28a-984b-903c-1f6451b04a15@linux.alibaba.com> <7d4e7f47-30a5-3cc6-dc9f-aa89120847d8@redhat.com> <64669c0a-4a6e-f034-a15b-c4a8deea9e5d@linux.alibaba.com> <7ee73879-e402-9175-eae8-41471d80d59e@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> + /* >> + * try_grab_page() should always succeed here, because we hold >> + * the ptl lock and have verified pte_present(). >> + */ >> + if (WARN_ON_ONCE(!try_grab_page(page, flags))) { >> + page = NULL; >> + goto out; >> + } >> + } else { > > Should add FOLL_MIGRATION validation before waiting a migration entry. We really only need FOLL_MIGRATION for KSM. As hugetlb pages cannot be KSM pages, we don't need this. Actually, I do have patches in the works that rip out FOLL_MIGRATION completely by adjusting KSM code. So let's try to not add dead code (although it would make sense for feature completeness as is -- but then, FOLL_MIGRATION really needs to go). -- Thanks, David / dhildenb