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b=nMz0+N96ip5jDNcW5D7tFlS/EcACY8E6gFUYn28kyxMnHSAwC12q3wo7xFCjnDqoe wLuAFuzSwvjWR/aiU/js5BUQ5glu3K5yC+qX5L4Iu/4QK2MH7Ceh5f0QX3hHZTCNWV hZ/OCcB4Ltzt1tLPIYv4F5n1yt/SQpZd04Ms/QWM= Date: Wed, 11 Jun 2025 17:19:50 -0700 From: Andrew Morton To: Kairui Song Cc: Chris Li , linux-mm@kvack.org, Barry Song <21cnbao@gmail.com>, Peter Xu , Suren Baghdasaryan , Andrea Arcangeli , David Hildenbrand , Lokesh Gidra , stable@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] mm: userfaultfd: fix race of userfaultfd_move and swap cache Message-Id: <20250611171950.5cb2d563c2935a93f5c7bbc0@linux-foundation.org> In-Reply-To: References: <20250604151038.21968-1-ryncsn@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 22EA61C000B X-Stat-Signature: s99rqrmpyumihm4j97amk9wboqcbdcs1 X-HE-Tag: 1749687592-210796 X-HE-Meta: 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 BTBiM9eo uo4ed6r0GrxL1kZ8KeSsnnQAp7PB3xe/FPPlanaMS1p5vlhfRk2PrrOOnZjoF0u4lLPwzKHlpw5T8sPPj+sK71FXtLogZZgdz1SCx2M+Oxk0zuHnbzUe2o1onOr0GImlxemTGStQoAZ25gL/VssuxvnO4E+CDP24JMEmftZZPVxkBKFc1SAz5IMMNOJBx4xwYJbQSCDxBd8v7iYwbHvIxk8CBETbSqw5i9VyeW8FmtCw7/7U0JsyccpYqD2JM1WLkWXtGpFfd8/WudAEflqloK+a7T/ys6sJqaVx1FSLHc13Ikg5/eRqvNzNfUIp+gFXxWkCU 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 Wed, 11 Jun 2025 13:16:25 +0800 Kairui Song wrote: > This commit fixes two kinds of races, they may have different results: > > Barry reported a BUG_ON in commit c50f8e6053b0, we may see the same > BUG_ON if the filemap lookup returned NULL and folio is added to swap > cache after that. > > If another kind of race is triggered (folio changed after lookup) we > may see RSS counter is corrupted: > > [ 406.893936] BUG: Bad rss-counter state mm:ffff0000c5a9ddc0 > type:MM_ANONPAGES val:-1 > [ 406.894071] BUG: Bad rss-counter state mm:ffff0000c5a9ddc0 > type:MM_SHMEMPAGES val:1 > > Because the folio is being accounted to the wrong VMA. > > I'm not sure if there will be any data corruption though, seems no. > The issues above are critical already. Thanks, I pasted this into the patch's changelog.