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b=QndkqMCxK1TeWqDkJY3Xr3u+beAQFaCzExSDnyjROfpnOQSf7l70VpJwfTJCuGdnF j67peCtt/5H0my3B5ITCB4HSiMCWCntjAvhxYlpGs1/oSfG5InVkbK8NShMAgAFIYr rQsw1xjH87dQkZE6IQci3tuUa2pyILrfU9+RrT7wd+L8mN+o/S7jkXq51bR675P11l hfU/eOWBHswnvbUXWr67rX9foP1NpibfBnSfNXkTg2TZz7g/v555sYClL8vV1AG7ZY r7S07bw6KTyVrCffSXxO8s3R/+sYR1ppC69d1zyINlTI9mUwicRhW5hEFlWw794qQP BxusL2gzAxyDQ== From: Thomas Gleixner To: Peter Zijlstra Cc: Hao-Yu Yang , mingo@redhat.com, linux-kernel@vger.kernel.org, Andrew Morton , David Hillenbrand , Eric Dumazet , linux-mm@kvack.org Subject: Re: [PATCH v2] futex: Use-after-free between futex_key_to_node_opt and vma_replace_policy In-Reply-To: <20260324140019.GE3738010@noisy.programming.kicks-ass.net> References: <20260313124756.52461-1-naup96721@gmail.com> <87a4vyihlx.ffs@tglx> <20260324140019.GE3738010@noisy.programming.kicks-ass.net> Date: Tue, 24 Mar 2026 17:36:42 +0100 Message-ID: <87fr5pgp5x.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 8040C140004 X-Stat-Signature: 6hacq45z6epxpohmpwaz1gf6p1frxtsj X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774370207-698964 X-HE-Meta: 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 xE8ANqCr adhNDiKNcM9UJIucxpZCzYmOwYepVRO02iq+xypUxTg2ocd1aEyTXJgQBEJg5vD5cWl+u7TxxtkCEyIkfZDlvCkNPF1ud//NBeldI+TMix5WcCaIQttT0/jTlc2IjmgQWvnPdM/itn2Q76+wqEUVSWrdkQCFHwYfVc0w1xVHeGCz57hoF05PDgjpJbT7OuiG6WEeQmW3uKlx2AAiOl1cEitK6/PvY7t5hlavlUYE1t87iVWCzwaX82an0vdEy58wB7NZVIjRJxRJhD7Br8yS91fiNOD4WftBK2kR1DSpYRx2rSnk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24 2026 at 15:00, Peter Zijlstra wrote: > On Mon, Mar 23, 2026 at 06:24:42PM +0100, Thomas Gleixner wrote: > Not to mention we don't actually need any of that here, because: > >> Especially the writer side is required so that the proper memory >> barriers are inserted for architectures with a weakly ordered memory >> model. > > The vma->vm_policy thing is written under mmap_lock held for writing, > and the futex consumer is a speculative read lock. Specifically the > ordering is through the associated seqcount. Duh. Yes. > All that is really needed is to extend the lifetime of the mpol to the > associated RCU period. Which is exactly what this patch does. > > Want me to go write up a better Changelog? And a comment in the code explaining the RCU magic perhaps?