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(p200300cbc7013100c642ba838c370b0e.dip0.t-ipconnect.de. [2003:cb:c701:3100:c642:ba83:8c37:b0e]) by smtp.gmail.com with ESMTPSA id m8-20020a7bca48000000b003fa96fe2bd9sm19977946wml.22.2023.08.15.00.11.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Aug 2023 00:11:17 -0700 (PDT) Message-ID: <76e6b2ad-4e1e-2ad3-95df-00b4d33ec9d2@redhat.com> Date: Tue, 15 Aug 2023 09:11:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [BUG] Re: [PATCH v3 10/13] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() To: Hugh Dickins , Jann Horn Cc: Andrew Morton , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Vasily Gorbik , Vishal Moola , Vlastimil Babka , Zi Yan , Linux ARM , sparclinux@vger.kernel.org, linuxppc-dev , linux-s390 , kernel list , Linux-MM References: <7cd843a9-aa80-14f-5eb2-33427363c20@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 28D1840010 X-Rspam-User: X-Stat-Signature: xdzxxhqafh9edzgmboh43bynyz7xs738 X-Rspamd-Server: rspam01 X-HE-Tag: 1692083481-829135 X-HE-Meta: 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 ZUpfW44O 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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: On 15.08.23 08:34, Hugh Dickins wrote: > On Mon, 14 Aug 2023, Jann Horn wrote: >> On Wed, Jul 12, 2023 at 6:42 AM Hugh Dickins wrote: >>> Bring collapse_and_free_pmd() back into collapse_pte_mapped_thp(). >>> It does need mmap_read_lock(), but it does not need mmap_write_lock(), >>> nor vma_start_write() nor i_mmap lock nor anon_vma lock. All racing >>> paths are relying on pte_offset_map_lock() and pmd_lock(), so use those. >> >> We can still have a racing userfaultfd operation at the "/* step 4: >> remove page table */" point that installs a new PTE before the page >> table is removed. >> >> To reproduce, patch a delay into the kernel like this: >> >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 9a6e0d507759..27cc8dfbf3a7 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -20,6 +20,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -1617,6 +1618,11 @@ int collapse_pte_mapped_thp(struct mm_struct >> *mm, unsigned long addr, >> } >> >> /* step 4: remove page table */ >> + if (strcmp(current->comm, "DELAYME") == 0) { >> + pr_warn("%s: BEGIN DELAY INJECTION\n", __func__); >> + mdelay(5000); >> + pr_warn("%s: END DELAY INJECTION\n", __func__); >> + } >> >> /* Huge page lock is still held, so page table must remain empty */ >> pml = pmd_lock(mm, pmd); >> >> >> And then run the attached reproducer against mm/mm-everything. You >> should get this in dmesg: >> >> [ 206.578096] BUG: Bad rss-counter state mm:000000000942ebea >> type:MM_ANONPAGES val:1 > > Thanks a lot, Jann. I haven't thought about it at all yet; and just > tried to reproduce, but haven't yet got the "BUG: Bad rss-counter": > just see "Invalid argument" on the UFFDIO_COPY ioctl. > Will investigate tomorrow. Maybe you're missing a fixup: https://lkml.kernel.org/r/20230810192128.1855570-1-axelrasmussen@google.com When the src address is not page aligned, UFFDIO_COPY in mm-unstable would erroneously fail. -- Cheers, David / dhildenb