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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A3DBC02180 for ; Wed, 15 Jan 2025 15:38:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1E8DE6B007B; Wed, 15 Jan 2025 10:38:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 199FA6B0082; Wed, 15 Jan 2025 10:38:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 060086B0083; Wed, 15 Jan 2025 10:38:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id DCD2D6B007B for ; Wed, 15 Jan 2025 10:38:56 -0500 (EST) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 899CC810E6 for ; Wed, 15 Jan 2025 15:38:56 +0000 (UTC) X-FDA: 83010094272.22.C6C8334 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf19.hostedemail.com (Postfix) with ESMTP id 858C41A0004 for ; Wed, 15 Jan 2025 15:38:54 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=HQS+Wf1G; spf=none (imf19.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1736955535; a=rsa-sha256; cv=none; b=bhoU9DqWHFrqVx7r88qKzs1k6ce96ZdWGAkYCPjC3BRO9wnRECFeCVkAKnZqn5640pF2TC dj4e7GeMXBHmSYgDm4qrjr9lDa3Kr/QgmIaiVmA9KkKR2SjWTV7E2e2kyjIXqlJg2i2ZmC 3+cq2QIpHYWedknVkdkY1otBwJo1J3w= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=HQS+Wf1G; spf=none (imf19.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1736955535; 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=xVMTvoVNKSDdrKhnVusgF0d6r3IQosvfTC+sagB7Qu8=; b=DuSRdA0Hl6Sf7rudjBfmPVkb6STlQcBzTrSlUt1eN7oE48pkkalDWx967BS1a+juHoUplo TWuDvQKRVXR1lkd27GjJRuFqWYdiBXq+iP3AbYeBo58QRFqlY+KwIQ8LLg9aQbY5R8N24R 4/xB63oPwclyp9i3ThmzT/aANBkhTek= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=xVMTvoVNKSDdrKhnVusgF0d6r3IQosvfTC+sagB7Qu8=; b=HQS+Wf1Gh8BwKH0blgSTZ9GJQr 38slONoFTED48nvcQy0B8hdzR2LFcKwI9pdINIGz5+wZZ4hOI8o7ftQ13R7OPS+ydw6n/VrZaqbco z5kf70dzXv99VuRRR2pTfaCfAfboiewOmY4t1FbUc3SdVIlXNazEn+JBcd7GNrmajUd9sM9iJu4Uo fqRDuaVQ2yRB8gL8Wzx1l+ho7z/iJyJ4GOQ6rmV9ucxIvG8/43hvOpaDBvM58LJTzfNneReSpFuQG uC5m16PQHP4s2zUQvd2U0OjwSJGBXfyJYpTrO7j/u3G2N0uu17F5DM7ak8M4ZuT0LYTty6gT26CZj 8cYJjJCw==; Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tY5Th-0000000AtFW-0uxM; Wed, 15 Jan 2025 15:38:45 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 0D0653004DE; Wed, 15 Jan 2025 16:38:44 +0100 (CET) Date: Wed, 15 Jan 2025 16:38:44 +0100 From: Peter Zijlstra To: Suren Baghdasaryan Cc: Mateusz Guzik , akpm@linux-foundation.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, david.laight.linux@gmail.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, 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, richard.weiyang@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 v9 11/17] mm: replace vm_lock and detached flag with a reference count Message-ID: <20250115153844.GF8385@noisy.programming.kicks-ass.net> References: <20250111042604.3230628-1-surenb@google.com> <20250111042604.3230628-12-surenb@google.com> <20250115104841.GX5388@noisy.programming.kicks-ass.net> <20250115111334.GE8385@noisy.programming.kicks-ass.net> <20250115153507.GF8362@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250115153507.GF8362@noisy.programming.kicks-ass.net> X-Rspamd-Queue-Id: 858C41A0004 X-Stat-Signature: md66s11btst7wmuhafw5eohcg3p9nnfr X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1736955534-708768 X-HE-Meta: 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 FW2AsVbK urm3Wp4DXlSp+jpKc940UC/AWTqAutmpWzyVxLAMl8aOAortSMm7JFD88d0gwpNN8IHxio5n0X/CzY+0TX9IRDWNBb7mf9FB9auXuINzUbsd5kOUikbUGQ+Z/WzR6Xa/m0xSoo4QkZR4cYp1w8um7JcScu6I7T+dWAgALqMU9OLycqnZL4RoclPpoie6hPB6MuO7pAZ0ad0s28OwzjOilLnVvev/3mIxSjpWOby2QcLP6gkoI2OUe/4XjdpcaKWdrVYaSmwH/7L37nOTTNhDyrHgJzIafT7blYATa/9o+OjuDLEqUZIrHJWrftA== 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, Jan 15, 2025 at 04:35:07PM +0100, Peter Zijlstra wrote: > Consider: > > CPU0 CPU1 > > rcu_read_lock(); > vma = vma_lookup(mm, vaddr); > > ... cpu goes sleep for a *long time* ... > > __vma_exit_locked(); > vma_area_free() > .. > vma = vma_area_alloc(); > vma_mark_attached(); > > ... comes back once vma is re-used ... > > vma_start_read() > vm_refcount_inc(); // success!! > > At which point we need to validate vma is for mm and covers vaddr, which > is what patch 15 does, no? Also, critically, we want these reads to happen *after* the refcount increment.