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 X-Spam-Level: X-Spam-Status: No, score=-5.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 103E8C28CC6 for ; Mon, 3 Jun 2019 17:35:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CDA26272C8 for ; Mon, 3 Jun 2019 17:35:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="jZtRRCEd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728402AbfFCRfj (ORCPT ); Mon, 3 Jun 2019 13:35:39 -0400 Received: from mail-lj1-f194.google.com ([209.85.208.194]:46673 "EHLO mail-lj1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726604AbfFCRfi (ORCPT ); Mon, 3 Jun 2019 13:35:38 -0400 Received: by mail-lj1-f194.google.com with SMTP id m15so8741397ljg.13 for ; Mon, 03 Jun 2019 10:35:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=1SfpobffKOrWKpwW04bKR3mmJHzrYDeRfbFX89KU/oE=; b=jZtRRCEdmQBOJG+Z5Up8Wy+HVMsB57ugBkXzh+rkJObgJLdoRJgQKS7nDZimjMzczG S3F4JvOrlWCxkK/z/bDgxnJY6URVrCDeXW239F+/VHZZ81wNElY2v7G1OpQcS5I9wS3V cSf1fcSFeDdhba9fTG2mUs0IncszXpghIDfP4G3Mcxydu7l8apcf6f9nyBvpqQ2e3LB9 +nKxYMfSCIlUDiplICylhbJ8YNz7gYuxTo8xJN4Ru3P+sgTjMWFYTXOe0MptITF/M9Oy beo5KkDFxhWrrHlzSQqKMdwlDCzajLk6/ckQFloacvBIgL6ze5EYrW3BD+mnusYRi1W3 5GZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=1SfpobffKOrWKpwW04bKR3mmJHzrYDeRfbFX89KU/oE=; b=fl1Ijtn81BouYVgSWFnJD3qTjaXNja+SJZj2ujAosbtPO27veX26/qlk3hMzSHm4VV kgdmL7HXQvN0EnMxQkRvOa4JLXZf1FCaC/b1ltliS0XarMT5Y1mnaLl/a3srVmqCE3EN YRx4somzmYcRgpGCYTxTgpAgpJapxQVgeTHXmXgGq3p7fvnpWkXFJNwsct88A1zQQgFY ln2C5rXROlAnO2tKI9STWIm+xteyuGbcO/GNOly07m3Ay0UMTiwhYY6HbEXe5JCYWRa5 2dNyC8O1S1TJxBJPNI5bBs1EjHSG9W/NpiV130jsxq+fZQuElwu472PZl92biRYmF90n h+7w== X-Gm-Message-State: APjAAAUAf9uwYmDmsG4EqSOOuf8/58kkBRr3gzg3ZeDldUmRN8fvDy/D ddVbg4HctphYOeh56fF/I5w= X-Google-Smtp-Source: APXvYqxDhmj7CdetUC52G+P/KDdFxFmprc9ZbFMlBQef2Z4kbsNDFuCKau2KhIv26tP0/iKhJ8ROwA== X-Received: by 2002:a2e:9a4f:: with SMTP id k15mr14550155ljj.159.1559583336440; Mon, 03 Jun 2019 10:35:36 -0700 (PDT) Received: from pc636 ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id q11sm3261148lfh.47.2019.06.03.10.35.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 03 Jun 2019 10:35:35 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 3 Jun 2019 19:35:28 +0200 To: Roman Gushchin Cc: Uladzislau Rezki , Andrew Morton , "linux-mm@kvack.org" , Hillf Danton , Michal Hocko , Matthew Wilcox , LKML , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Joel Fernandes , Thomas Gleixner , Ingo Molnar , Tejun Heo Subject: Re: [PATCH v3 4/4] mm/vmap: move BUG_ON() check to the unlink_va() Message-ID: <20190603173528.7ukfgznmiypzfyze@pc636> References: <20190527093842.10701-1-urezki@gmail.com> <20190527093842.10701-5-urezki@gmail.com> <20190528225001.GI27847@tower.DHCP.thefacebook.com> <20190529135817.tr7usoi2xwx5zl2s@pc636> <20190529162638.GB3228@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529162638.GB3228@tower.DHCP.thefacebook.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Roman! On Wed, May 29, 2019 at 04:26:43PM +0000, Roman Gushchin wrote: > On Wed, May 29, 2019 at 03:58:17PM +0200, Uladzislau Rezki wrote: > > Hello, Roman! > > > > > > Move the BUG_ON()/RB_EMPTY_NODE() check under unlink_va() > > > > function, it means if an empty node gets freed it is a BUG > > > > thus is considered as faulty behaviour. > > > > > > It's not exactly clear from the description, why it's better. > > > > > It is rather about if "unlink" happens on unhandled node it is > > faulty behavior. Something that clearly written in stone. We used > > to call "unlink" on detached node during merge, but after: > > > > [PATCH v3 3/4] mm/vmap: get rid of one single unlink_va() when merge > > > > it is not supposed to be ever happened across the logic. > > > > > > > > Also, do we really need a BUG_ON() in either place? > > > > > Historically we used to have the BUG_ON there. We can get rid of it > > for sure. But in this case, it would be harder to find a head or tail > > of it when the crash occurs, soon or later. > > > > > Isn't something like this better? > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index c42872ed82ac..2df0e86d6aff 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -1118,7 +1118,8 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier); > > > > > > static void __free_vmap_area(struct vmap_area *va) > > > { > > > - BUG_ON(RB_EMPTY_NODE(&va->rb_node)); > > > + if (WARN_ON_ONCE(RB_EMPTY_NODE(&va->rb_node))) > > > + return; > > > > > I was thinking about WARN_ON_ONCE. The concern was about if the > > message gets lost due to kernel ring buffer. Therefore i used that. > > I am not sure if we have something like WARN_ONE_RATELIMIT that > > would be the best i think. At least it would indicate if a warning > > happens periodically or not. > > > > Any thoughts? > > Hello, Uladzislau! > > I don't have a strong opinion here. If you're worried about losing the message, > WARN_ON() should be fine here. I don't think that this event will happen often, > if at all. > If it happens then we are in trouble :) I prefer to keep it here as of now, later on will see. Anyway, let's keep it and i will update it with: if (WARN_ON(RB_EMPTY_NODE(&va->rb_node))) return; Thank you for the comments! -- Vlad Rezki