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[2003:d8:2f38:b600:7d6d:5e38:70ec:12c6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f73d4a3csm193343385e9.22.2025.05.24.14.48.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 May 2025 14:48:03 -0700 (PDT) Message-ID: <5815d9ed-e59f-4129-b20b-a0c07a2cf874@redhat.com> Date: Sat, 24 May 2025 23:48:01 +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 2/2] mm/khugepaged: fix race with folio split/free using temporary reference To: Shivank Garg , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, fengwei.yin@intel.com, bharata@amd.com, syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com References: <20250523091432.17588-1-shivankg@amd.com> <20250523091432.17588-2-shivankg@amd.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 23.05.25 11:14, Shivank Garg wrote: > hpage_collapse_scan_file() calls folio_expected_ref_count(), which in turn > calls folio_mapcount(). folio_mapcount() checks folio_test_large() before > proceeding to folio_large_mapcount(), but there is a race window where the > folio may get split/freed between these checks, triggering: > > VM_WARN_ON_FOLIO(!folio_test_large(folio), folio) > > Take a temporary reference to the folio in hpage_collapse_scan_file(). > This stabilizes the folio during refcount check and prevents incorrect > large folio detection due to concurrent split/free. > > Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") > Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com > Suggested-by: David Hildenbrand > Signed-off-by: Shivank Garg > --- > V1: https://lore.kernel.org/linux-mm/20250522093452.6379-1-shivankg@amd.com > --- Assuming we have this as patch #1: Acked-by: David Hildenbrand -- Cheers, David / dhildenb