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 D1432C4345F for ; Fri, 12 Apr 2024 14:17:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 66FA76B0096; Fri, 12 Apr 2024 10:17:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 620296B0098; Fri, 12 Apr 2024 10:17:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4E9006B009A; Fri, 12 Apr 2024 10:17:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 31BAF6B0096 for ; Fri, 12 Apr 2024 10:17:01 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id B1E041607D5 for ; Fri, 12 Apr 2024 14:17:00 +0000 (UTC) X-FDA: 82001081400.28.F190B90 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf06.hostedemail.com (Postfix) with ESMTP id 99EE0180009 for ; Fri, 12 Apr 2024 14:16:57 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rMMjDlI5; dmarc=none; spf=none (imf06.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1712931419; 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=9XUEwsNrmwFS+p7W60FkPz2435AkFdskzYLram0Y5Po=; b=7i0/P7iTUBaNVIAZbh+z+PITnVY3c7rLh550YNOds1IAnFCKR4gzMe/mm2G2AFsQhtZGG3 5GbzYhUQqbVFL1jBtiBZfjUo0PtpDSV1G+d5QXPvXnZP0Y33xpOA57Zt5iia9GJ4+AErvy a4fs+JmWf046y3kLcAto/uQ//CqcUVg= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rMMjDlI5; dmarc=none; spf=none (imf06.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1712931419; a=rsa-sha256; cv=none; b=RWOh+qub7gh6EUy+gJ3dccCMCR+feQlo6MUsJGOVrUVIV/1Po/X0MhqHwoOzvpFwWzr7Nm E4bjAe4BelOSpDrEDEu+lQ6Cu4b0HVI5XDaIDRCW4SDn1XKJW5dXmIb66AtnApTK983rPI PnEs/u9B4SbnV0fgPVEAU8vmcGsdFmE= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=9XUEwsNrmwFS+p7W60FkPz2435AkFdskzYLram0Y5Po=; b=rMMjDlI54eaUpy5OL5nSWfkC23 FehjGUZqbI9e/lAI9EOrn8i52GbhtJL7oGdZjxdoTVQ7w0vv11p5Wy4FK6dqUJCUy7L1/SEAuCvqE 3270273qJeR+Oql+gYffuogIozJ5Hwq57BMbrPBf9HVZv11WmDYgAGU1C1rOmuecU5DCHzs9SNEbb 8MZcVUPgb8rwDhcgRTwPBmFRhrK1fk0G4gKTBQnDpV7C51KXMntCzciG04wGb2fTjqk1AFeIt+qG+ pGiHHCitqVA1fJItD1N0HGiU98DR2d4d7WqmHndRBLHXlbV17MBgpUOxDTqxL/8QhcHf6hDPP/TLa BoiD6Dqw==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rvHi0-00000009P8j-3kM6; Fri, 12 Apr 2024 14:16:53 +0000 Date: Fri, 12 Apr 2024 15:16:52 +0100 From: Matthew Wilcox To: Suren Baghdasaryan Cc: Peter Xu , "Liam R. Howlett" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lokesh Gidra , Alistair Popple Subject: Re: [PATCH] mm: Always sanity check anon_vma first for per-vma locks Message-ID: References: <20240410170621.2011171-1-peterx@redhat.com> <20240411171319.almhz23xulg4f7op@revolver> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 99EE0180009 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: rmnnxkemgaumyxfenc63yoar1bq87n5h X-HE-Tag: 1712931417-193435 X-HE-Meta: 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 Y5prDvof 5Wd4IVvzIJ7lk1JgpgwXo3249a8vJ0+VD5GuPqEaRAnKY6F9mS0354dnm+Whl4M4z3hZ65m+/Y9csmAgWT8XAq5zUBrH/1mEnZxsF9D1jRVLzQRd6t9PwdjPJQXNKSMESS1zSdBFXdeTIa8juGH2dhr6VtmH+lWzyu0vXW0NplbrGMWAqc0Lst3564g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000016, 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 Fri, Apr 12, 2024 at 06:06:46AM -0700, Suren Baghdasaryan wrote: > > On Fri, Apr 12, 2024 at 04:14:16AM +0100, Matthew Wilcox wrote: > > > - /* > > > - * find_mergeable_anon_vma uses adjacent vmas which are not locked. > > > - * This check must happen after vma_start_read(); otherwise, a > > > - * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA > > > - * from its anon_vma. > > > - */ > > > - if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) > > > - goto inval_end_read; > > > - > > > /* Check since vm_start/vm_end might change before we lock the VMA */ > > > if (unlikely(address < vma->vm_start || address >= vma->vm_end)) > > > goto inval_end_read; > > > > > > That takes a few insns out of the page fault path (good!) at the cost > > > of one extra trip around the fault handler for the first fault on an > > > anon vma. It makes the file & anon paths more similar to each other > > > (good!) > > > > > > We'd need some data to be sure it's really a win, but less code is > > > always good. > > I agree, if we make this change we should keep this comment and maybe > move it into vmf_anon_prepare() Most of the comment makes no sense if you move it out of lock_vma_under_rcu(). It's justifying where it needs to be in that function. If it's no longer in that function, there's not much left of the comment. What part do you think is valuable and needs to be retained?