From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77AC9C982FA for ; Tue, 22 Sep 2026 17:22:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5404B6B0092; Tue, 22 Sep 2026 13:22:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 518FE6B0095; Tue, 22 Sep 2026 13:22:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3E1116B0098; Tue, 22 Sep 2026 13:22:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 1F1E56B0092 for ; Tue, 22 Sep 2026 13:22:42 -0400 (EDT) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 958AF1A0563 for ; Tue, 22 Sep 2026 17:22:41 +0000 (UTC) X-FDA: 85242067722.07.D0247A4 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf17.hostedemail.com (Postfix) with ESMTP id E310340007 for ; Tue, 22 Sep 2026 17:22:39 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="F9l/h2sg"; spf=pass (imf17.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790097759; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=UNh8IajC2C7W4xAVN/5A4Te3DbNvUnFRUUUmja4mmRU=; b=TPQ3psGKA/P6fakKxvR6thLwisXJjMvVGt9Vd++QpW6WT9NjzXxviOMeXEdY5KxRPZJaNw pa5SxnLtn5slV1oG00hdtxJS5VpATyc0d9CuOwul2zw54yPap3KCq60m2dSW9yLC6OWX3r JYCO9nc64oN6+i8lki0rm+z5edv1jTw= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="F9l/h2sg"; spf=pass (imf17.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790097759; b=yhdIN8ECIolK2hQdh7YeiPeuNBPn/hmCJOzYtVPXRp+pDwxuqy8FqItrwkxclZeeNh0NUP wvjnFmVmH/tD/DkX4EIW1OPmejCrEKkhDltJh2fLqWe+QXbEfIuACmCTfSUR5KfM5MQ+Xg F4fyLd1cMESe9XLE6QRlMXpAK8P5C6g= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 4EC096022B; Tue, 22 Sep 2026 17:22:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 04DCD1F000FF; Tue, 22 Sep 2026 17:22:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790097759; bh=UNh8IajC2C7W4xAVN/5A4Te3DbNvUnFRUUUmja4mmRU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=F9l/h2sgeG6pItIpsl4UOUD5LPuOPYalAOj3lX7iN1SKQRQx/7vSe8Y8wJYuJaFa9 tegjTwQVFA9hXGIt+1oJvFwKspvEmTZEeRl/rL3Z+1/vMB7N90Y9ljH8EiqVFiWGMa llb7G+u8p4G82Y3NfZpa4T6VyMnit/o1genoOGjAzyku0OZj1fvAIP0nPa5BRjaZ1s 0LsiYA1bWAjQ698sUHV9gBhPhcHOkUs5jCvX2Aqi8QkSHyLlAciZyH7C9FEowKSWF8 GvrRJLzG6nhqL2FhCQxRW0vNDBGCdIskECu8iSBeB5zhpcl0fRPI9Q5+bVasWrDLde t0gfKdsjFaNOA== Date: Tue, 22 Sep 2026 18:22:15 +0100 From: "Lorenzo Stoakes (ARM)" To: Matthew Wilcox Cc: Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Guo Ren , Brian Cain , Geert Uytterhoeven , Dinh Nguyen , Simon Schuster , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Rich Felker , John Paul Adrian Glaubitz , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Russell King , Vineet Gupta , Michal Simek , Chris Zankel , Max Filippov , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , "David S. Miller" , Andreas Larsson , Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Mark Rutland , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Richard Weinberger , Anton Ivanov , Johannes Berg , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jason Gunthorpe , John Hubbard , Peter Xu , Yoshinori Sato , Shakeel Butt , Jonathan Corbet , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-alpha@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-um@lists.infradead.org, Hugh Dickins , Qi Zheng , linux-doc@vger.kernel.org Subject: Re: [PATCH v4 00/12] mm: make userland page table freeing RCU-safe Message-ID: References: <20260922-rcu-pagetable-freeing-v4-0-fe1ad1f1e303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: e39zbxrp7g8joyjtw7rnnau7mc4wzrey X-Rspamd-Queue-Id: E310340007 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1790097759-917956 X-HE-Meta: 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 qzyJ+w3x O0npjSmnT/HTcbvTv0loshEEZKp9LEzeXTi3fdumFBDEMQaokLuF/9VP/QCbMJap/GKQdsQjViXlwqECDdZ34mi5fLxCVxYcAfqaSv9cEVf+qg9WwpjEMByiVnQZ7tk599kLYp65ISVm3K4IvAMzGeuMp6ZknLRo7BjP8IVv1M1m5Pdv9wqBIVOyDufac8g/quTPAZdDMUi/riWlU0AqXUT2U2949r+cW2MCtOQAQ53x2BzoxbKi4f/MPgLI2ccJHpwn2hRhJDOKB3WemgehdhaWkLFIVE9ItQ3OPDbNN4mEoB1Vo2LfCEC+ntBwK3l1Xy5CKRkQsaJRs/Mw= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 22, 2026 at 05:42:10PM +0100, Matthew Wilcox wrote: > On Tue, Sep 22, 2026 at 04:35:31PM +0100, Lorenzo Stoakes (ARM) wrote: > > m68k-motorola required the biggest change - since RCU page table freeing > > uses call_rcu(), this means page table freeing can arise from softirq > > context. > > > > This was fixed with an IRQ-safe spin lock used in both get_pointer_table() > > and free_pointer_table(). > > You don't need to use an irq-safe spinlock for softirqs. It does work, > but it's overkill since it disables hardirqs. If you use spin_lock_bh(), > only softirqs are prevented from running (and it's safe to call > spin_lock_bh() when in softirq context, just like it's safe to call > spin_lock_irqsave() in hardirq or softirq context). Right yup, I know _bh() is fine for softirq, I think this was being overly cautious (for sparc32 you do actually need irq saving). But this is m68k :) functionally there's really not that much difference, and it's over very few instrucitons so the delta here is likely to be functionally little to nothing. If I need to respin again I'll fix it up! -- Cheers, Lorenzo