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b=JbknlN2pyXxa62LpH3djtmN7GfJwtM9i/YXPq0QOf//aefZu5ftNzsreiJEkq4ILgWZwHY6WeaimaOFh3nzczshO9UBhz0duT5QWAXjFm3tCDqSUtra+5OvO/sTN+j5etKYo0Bdir96yMT127WYtrtNoOAdDEsAmjEbCEQmhVuU= Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; Received: from AM9PR08MB7120.eurprd08.prod.outlook.com (2603:10a6:20b:3dc::22) by DB9PR08MB6601.eurprd08.prod.outlook.com (2603:10a6:10:23e::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8769.21; Thu, 22 May 2025 10:02:31 +0000 Received: from AM9PR08MB7120.eurprd08.prod.outlook.com ([fe80::2933:29aa:2693:d12e]) by AM9PR08MB7120.eurprd08.prod.outlook.com ([fe80::2933:29aa:2693:d12e%2]) with mapi id 15.20.8769.019; Thu, 22 May 2025 10:02:30 +0000 Message-ID: <47ff4f56-6bc0-4e7f-8b71-765a08a4cac4@arm.com> Date: Thu, 22 May 2025 15:32:24 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/khugepaged: Fix race with folio splitting in hpage_collapse_scan_file() To: Shivank Garg , akpm@linux-foundation.org, david@redhat.com, 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, fengwei.yin@intel.com, bharata@amd.com, syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com References: <20250522093452.6379-1-shivankg@amd.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20250522093452.6379-1-shivankg@amd.com> Content-Type: text/plain; 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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 May 2025 10:03:03.7002 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 145fc17f-69a1-46ed-7e1f-08dd9917d7a9 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DU6PEPF0000A7DE.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB7801 X-Stat-Signature: hp67n43j8if4nz9ue79c1hn476jjqbqi X-Rspamd-Queue-Id: 81ADCA001D X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1747908189-973787 X-HE-Meta: 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 ONoqr5cS jl0RNfaJOH6XRnnNPHCeHYCHhHMcH6DFQ4FwievhOJPBENmYPv/F61t2Jdf7W28iSTFzVJbBHmXhsjbfZS1fGU0Ne2n0z642jk195GD0h9k74+PTMNiuOlVvBgCi9cuYFRUv7cXWiuE6lp8LNNeDGiLuttDQ01hkxPOvwY10brqO+LN0ThmfpWWMAqjMjt/FMYAzN0r7SgI9ru8HIb0MmjcolArRGOVyuVB9sWmBmvVjLCgfLGt43yCOzaOZhvfoWCRZSGj4/y7CUJN2vYDitxdkbm5Jb1mZru2tY+YEgpR+njednm77bE3p1OpQ9okImqoSlvZ9Y8YdZDn6k2sBTWPj+iQYJVlCv3So44lHBNooimzFMYSZG/daysV9EbKK3YGsZ9yV3joZ14ZTEaTuz6weoCK00IPCfj1iIoTlm9B4abzmoyzSAh/DY3MhIGv/+n+GGqToPDKjj9nOrwF7PCePECr8hKBXLBlkxkpraHQ/KgR4hh3YkoeG9rzqJ/GFyCjxvs4eKRryys2P4mWvOhncTbndFQCHzbtxkyeofXb9bw4S44zRg8X/Vtl+MgNZncp17QVjgfoVveWSxZaTjkEwLbtlu8qTj79tBLqY+LvJJmaPuMU4s4ijtlxUHPzdNIwm4G5mF1uPtjjV2YDvR8nKRVFGlsSzhni75MnJ/1jAy5RH9ZYXdu+r4kY8lxY/H0VKjjfscYkpZaM+uvVCEl4oN5/ymJm7+Lzi66Y8fumxltRyW/IdumDnLR/tL8jUyoeoT3BHGmQwQIi+Cte2idpUOIqzde2PvYzXZTrHb6RyHTLmaOeRjgWDqFetjl0dQuMj2jnRjcIl1cgScE/vGT0XX5i2Z+W7WB/FgL0QRxAu6LWV2RDwxEtJXwZfjVgHGaW2B 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: On 22/05/25 3:04 pm, Shivank Garg wrote: > folio_mapcount() checks folio_test_large() before proceeding to > folio_large_mapcount(), but there exists a race window where a folio > could be split between these checks which triggered the > VM_WARN_ON_FOLIO(!folio_test_large(folio), folio) in > folio_large_mapcount(). > > Take a temporary folio reference in hpage_collapse_scan_file() to prevent > races with concurrent folio splitting/freeing. This prevent potential > incorrect large folio detection. > > Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6828470d.a70a0220.38f255.000c.GAE@google.com > Fixes: 05c5323b2a34 ("mm: track mapcount of large folios in single value") > Suggested-by: David Hildenbrand > Signed-off-by: Shivank Garg > --- > mm/khugepaged.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index cc945c6ab3bd..6e8902f9d88c 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2295,6 +2295,17 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > continue; > } > > + if (!folio_try_get(folio)) { > + xas_reset(&xas); > + continue; > + } > + > + if (unlikely(folio != xas_reload(&xas))) { > + folio_put(folio); > + xas_reset(&xas); > + continue; > + } > + > if (folio_order(folio) == HPAGE_PMD_ORDER && > folio->index == start) { > /* Maybe PMD-mapped */ > @@ -2305,23 +2316,27 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > * it's safe to skip LRU and refcount checks before > * returning. > */ > + folio_put(folio); > break; > } > > node = folio_nid(folio); > if (hpage_collapse_scan_abort(node, cc)) { > result = SCAN_SCAN_ABORT; > + folio_put(folio); > break; > } > cc->node_load[node]++; > > if (!folio_test_lru(folio)) { > result = SCAN_PAGE_LRU; > + folio_put(folio); > break; > } > > if (!is_refcount_suitable(folio)) { Do we need to change is_refcount_suitable()? > result = SCAN_PAGE_COUNT; > + folio_put(folio); > break; > } > > @@ -2333,6 +2348,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, > */ > > present += folio_nr_pages(folio); > + folio_put(folio); > > if (need_resched()) { > xas_pause(&xas);