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Howlett" , "Lorenzo Stoakes" , "David Hildenbrand" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20261013191719.95502-1-pfalcato@suse.de> In-Reply-To: <20261013191719.95502-1-pfalcato@suse.de> X-ClientProxiedBy: CH0PR03CA0068.namprd03.prod.outlook.com (2603:10b6:610:cc::13) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|DS4PR12MB999100:EE_ X-MS-Office365-Filtering-Correlation-Id: 44211642-29aa-4951-0c3f-08df2a0685ec X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|376014|7416014|366016|261009223027099003|11063799006|56012099006|18002099003|22082099003|10067099003|3023799007; X-Microsoft-Antispam-Message-Info: zzNVHzMDL9uctjcOurr52edyViN3Z6Wtz21s31uPdgMRODGrsn3pyPOM/eYpgfm7xFU0XcnGBm2jgzaUCmld7BQvo0Qz7GBimOVUKuez6vX+Guxn4zRDrdfBff9wzMI6AsrP8B39Odt6WbEdVxJj75by1DHSooLjDzoquZ2p94UfNEcptZ/ThzwyiMxj0uvGB6fOjefY3dzshTKE9YE2IgQrjDwS08DzxaW0JsWnGdN98w4fpLDCAoBhmZkV7wVw7JGWgyVBcQjbWvO79aNJ7OZjH3ldo/3vBGfUbNtt8FMiQDSx1ISWAFqp8tgu3kwOdcjk0T0mrWzLHwfm6vzBpueb4gWd/D3wH1MJLbkrcmxCtXOlriRWuf1lfJLSLbeNvkAf6y3kX+buiIWKHnMoWzc07/RBOFiZDMbkcLmMjd4g3p2BWH5WYmD8sKSIKQiJ2hp7jgq3Ejw+uIEx+G8ni+Efc2tusVFrIIShXkEbbZ9uogJFCjeKuN1Z+KKPw57IMJRnmNpNprlM6pufzt74Y5soM44tnlJGp2BkT0a39Y7wHgdMouRTHr9LU6g7zcgbArhd6+9jK/d5W0OyU2+zuapzinSS98vD2ifZJ6KpxJXyZJnlSn+AHjN+BXaW5SJmWajHHFD3vK67iVZ5gkflp5RFuPOErLNEbsg1NYESWvE= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:IA0PR12MB8374.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(23010399003)(1800799024)(376014)(7416014)(366016)(261009223027099003)(11063799006)(56012099006)(18002099003)(22082099003)(10067099003)(3023799007);DIR:OUT;SFP:1101; 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However, it does so in a racy manner, looking at a > possibly-stale snapshot. It's entirely possible that a write elsewhere > set the hardware D bit, which this logic now loses. > > Fix it by using pmdp_test_and_clear_young(). This is an atomic > modification of the PMD entry, and thus safe against any possible racing > writes. As a (nice) side-effect, this elides one non-required TLB flush > in pmdp_invalidate(). > > This bug can interact with the swapping system in complicated ways, leadi= ng > to data loss. For instance, if a folio is marked lazyfree, but was later > read from, and then MADV_COLD'd while racing a write to that same THP, > dropping the dirty bit may lead to data loss as reclaim/MADV_PAGEOUT drop= s > the "clean" anon folio: > > T0 T1 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > MADV_FREE(thp) | > folio marked lazyfree | > read(thp) | > PMD marked young by hardware | > | MADV_COLD(thp) > write(thp) | if (pmd_young(pmd)) { > PMD marked dirty by hardware | set(pmdp, pmd_mkold(pmd)); > MADV_PAGEOUT/reclaim | > dirty bit may or may not be | > set | > reclaim/pageout may drop | > the folio | > > Fixes: 9c276cc65a58 ("mm: introduce MADV_COLD") > Cc: stable@vger.kernel.org > Reported-by: Samarth Narang > Closes: https://lore.kernel.org/linux-mm/20261011132227.413217-1-samarth.= colleges@gmail.com/ > Signed-off-by: Pedro Falcato > --- > mm/madvise.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > LGTM. Acked-by: Zi Yan --=20 Best Regards, Yan, Zi