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Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Alexander Shishkin , Maxime Coquelin , Alexandre Torgue , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Bodo Stroesser , "Martin K . Petersen" , David Howells , Marc Dionne , Alexander Viro , Christian Brauner , Jan Kara , David Hildenbrand , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-mtd@lists.infradead.org, linux-staging@lists.linux.dev, linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Ryan Roberts Subject: Re: [PATCH v3 04/16] mm: add vm_ops->mapped hook Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EDE88C0007 X-Stat-Signature: gzzmujfepttfhea4wcnbeycmg7bo8pww X-Rspam-User: X-HE-Tag: 1774039413-669963 X-HE-Meta: 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 eZVnt/6j UcbUyAb1HwtDDiHLpCXdECdbu99t3mEPFFZyaDOinmSXfuO5ND96GA9N19SrbtXKkTnqGZwRV2Yv1TnXY58Cvy8aN27AumBMRFQqAIremM3/qqT7Mso77jSvgzS48Xi6gYKGGtrG2bnM5LiuRZANTXh80An+fUrCRACWsQTEgnrFh1VaMQnSlxKAePQwLWldPYuE/WxFhYAhUmwzubnzG7FK/TDp1KNP2oXYC3GRBhcW2hWqrgA/PwMxdxfmJwLwB93DrikdvfgLQLVLtMPM0Q6FM3T6migQTrRsjbYEbEM71PuuyvwVBCfxfYS1SwqtynLMv9b/UUBEbN4c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 20, 2026 at 07:26:37PM +0100, Vlastimil Babka (SUSE) wrote: > On 3/19/26 19:23, Lorenzo Stoakes (Oracle) wrote: > > Previously, when a driver needed to do something like establish a > > reference count, it could do so in the mmap hook in the knowledge that the > > mapping would succeed. > > > > With the introduction of f_op->mmap_prepare this is no longer the case, as > > it is invoked prior to actually establishing the mapping. > > > > mmap_prepare is not appropriate for this kind of thing as it is called > > before any merge might take place, and after which an error might occur > > meaning resources could be leaked. > > > > To take this into account, introduce a new vm_ops->mapped callback which > > is invoked when the VMA is first mapped (though notably - not when it is > > merged - which is correct and mirrors existing mmap/open/close behaviour). > > > > We do better that vm_ops->open() here, as this callback can return an > > error, at which point the VMA will be unmapped. > > > > Note that vm_ops->mapped() is invoked after any mmap action is complete > > (such as I/O remapping). > > > > We intentionally do not expose the VMA at this point, exposing only the > > fields that could be used, and an output parameter in case the operation > > needs to update the vma->vm_private_data field. > > > > In order to deal with stacked filesystems which invoke inner filesystem's > > mmap() invocations, add __compat_vma_mapped() and invoke it on vfs_mmap() > > (via compat_vma_mmap()) to ensure that the mapped callback is handled when > > an mmap() caller invokes a nested filesystem's mmap_prepare() callback. > > > > We can now also remove call_action_complete() and invoke > > mmap_action_complete() directly, as we separate out the rmap lock logic. > > > > The rmap lock logic, which was added in order to keep hugetlb working (!) > > to allow for the rmap lock to be held longer, needs to be propagated to the > > error paths on mmap complete and mapped hook error paths. > > > > This is because do_munmap() might otherwise deadlock with the rmap being > > held, so instead we unlock at the point of unmap. > > Hmm but that was also true prior to this series? So is this a bugfix? Should > it be a stable hotfix done outside of the series before the refactoring? Yup, will send a hotfix. Thanks, Lorenzo