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Wong" , Christoph Hellwig , John Hubbard , , , , , Subject: Re: [PATCH v2 05/18] xfs: Add xfs_break_layouts() to the inode eviction path Message-ID: <632d00a491d0d_4a67429488@dwillia2-xfh.jf.intel.com.notmuch> References: <166329930818.2786261.6086109734008025807.stgit@dwillia2-xfh.jf.intel.com> <166329933874.2786261.18236541386474985669.stgit@dwillia2-xfh.jf.intel.com> <20220918225731.GG3600936@dread.disaster.area> <632894c4738d8_2a6ded294a@dwillia2-xfh.jf.intel.com.notmuch> <20220919212959.GL3600936@dread.disaster.area> <6329ee04c9272_2a6ded294bf@dwillia2-xfh.jf.intel.com.notmuch> <20220921221416.GT3600936@dread.disaster.area> <20220923001846.GX3600936@dread.disaster.area> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20220923001846.GX3600936@dread.disaster.area> X-ClientProxiedBy: BYAPR08CA0050.namprd08.prod.outlook.com (2603:10b6:a03:117::27) To MWHPR1101MB2126.namprd11.prod.outlook.com (2603:10b6:301:50::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MWHPR1101MB2126:EE_|DS0PR11MB6472:EE_ X-MS-Office365-Filtering-Correlation-Id: a3fbaecb-b50e-4f22-85f4-08da9cfc505d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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bh=XflN0Hp/URuVhTKrxjinxniEL3BoWmH0T0hpjdDAjfs=; b=oT+De/s3Esn9S8lhrvOfONDLQ8XkYp3XneSIPbECNITgYhbJJm/EsDbDIP+ENcvjyDfdSN z/aChrb74x9Zxy5vPRKazFK4idjdM8HWHaK5N2jN6K+qJqlRbWHdVEbSTrgZra5EbBYgw4 GgaSRNtVeaXQ+LSpAjL/isDIRs52sD0= X-Stat-Signature: fpgaus3dw6be87wgrmbenpcsae5ku7jm X-Rspamd-Queue-Id: 488ED1A000A X-Rspam-User: X-Rspamd-Server: rspam08 Authentication-Results: imf19.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=hfO6U2Xq; spf=pass (imf19.hostedemail.com: domain of dan.j.williams@intel.com designates 192.55.52.93 as permitted sender) smtp.mailfrom=dan.j.williams@intel.com; arc=reject ("signature check failed: fail, {[1] = sig:microsoft.com:reject}"); dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1663893677-620462 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: Dave Chinner wrote: > On Wed, Sep 21, 2022 at 07:28:51PM -0300, Jason Gunthorpe wrote: > > On Thu, Sep 22, 2022 at 08:14:16AM +1000, Dave Chinner wrote: > > > > > Where are these DAX page pins that don't require the pin holder to > > > also hold active references to the filesystem objects coming from? > > > > O_DIRECT and things like it. > > O_DIRECT IO to a file holds a reference to a struct file which holds > an active reference to the struct inode. Hence you can't reclaim an > inode while an O_DIRECT IO is in progress to it. > > Similarly, file-backed pages pinned from user vmas have the inode > pinned by the VMA having a reference to the struct file passed to > them when they are instantiated. Hence anything using mmap() to pin > file-backed pages (i.e. applications using FSDAX access from > userspace) should also have a reference to the inode that prevents > the inode from being reclaimed. > > So I'm at a loss to understand what "things like it" might actually > mean. Can you actually describe a situation where we actually permit > (even temporarily) these use-after-free scenarios? Jason mentioned a scenario here: https://lore.kernel.org/all/YyuoE8BgImRXVkkO@nvidia.com/ Multi-thread process where thread1 does open(O_DIRECT)+mmap()+read() and thread2 does memunmap()+close() while the read() is inflight. Sounds plausible to me, but I have not tried to trigger it with a focus test.