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Howlett" , akpm@linux-foundation.org, willy@infradead.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v6 10/16] mm: replace vm_lock and detached flag with a reference count Message-ID: <20241218161850.GG2354@noisy.programming.kicks-ass.net> References: <20241216192419.2970941-1-surenb@google.com> <20241216192419.2970941-11-surenb@google.com> <20241216213753.GD9803@noisy.programming.kicks-ass.net> <20241217103035.GD11133@noisy.programming.kicks-ass.net> <20241218094104.GC2354@noisy.programming.kicks-ass.net> <20241218100601.GI12500@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: e59697rgmd9uc4pux3jsfcqk85hnqcf5 X-Rspam-User: X-Rspamd-Queue-Id: 2E28BA002D X-Rspamd-Server: rspam08 X-HE-Tag: 1734538690-102397 X-HE-Meta: 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 ahJECUSu R/rah4YCoKh1V2IGBSdFj5M1WM46WgmHT8AW9kvJ+xF3TM7d2VVMzsVkJwaPAyDWW0J8Wl+uzs7sqav460ATwANjGS8B7wFVE+8jtcG6NvGNqFQJ+oJfxb0NYyygQj024srjP9acmhY49/OcjdlXcWYHTN4h0acdx8v3OWXFunLTj7V7dlTlaqu/70weqM0ERdDwJuNBpO30YOMWRRqJhtWu0Q3N8a4RkjDkNkyuVo9rG1aPQ+GuQq/qRuQ== 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, Dec 18, 2024 at 07:50:34AM -0800, Suren Baghdasaryan wrote: > I think vma_start_write() should be done inside > vms_gather_munmap_vmas() for __mmap_prepare() to work correctly: > > __mmap_prepare > vms_gather_munmap_vmas > vms_clean_up_area // clears PTEs > ... > __mmap_complete > vms_complete_munmap_vmas I'm unsure what exactly you mean; __split_vma() will start_write on the one that is broken up and the rest won't actually change until vms_complete_munmap_vmas(). > If we do not write-lock the vmas inside vms_gather_munmap_vmas(), we > will be clearing PTEs from under a discoverable vma. You will not. vms_complete_munmap_vmas() will call remove_vma() to remove PTEs IIRC, and if you do start_write() and detach() before dropping mmap_lock_write, you should be good. > There might be other places like this too but I think we can move > vma_mark_detach() like you suggested without moving vma_start_write() > and that should be enough. I really don't see why you can't move vma_start_write() -- note that by moving that after you've unhooked the vmas from the mm (which you have by that point) you get the sync point you wanted.