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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 7A5B5C5ACCC for ; Tue, 16 Oct 2018 19:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 47DDB21470 for ; Tue, 16 Oct 2018 19:40:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 47DDB21470 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727627AbeJQDcX (ORCPT ); Tue, 16 Oct 2018 23:32:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:48796 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727154AbeJQDcX (ORCPT ); Tue, 16 Oct 2018 23:32:23 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DF1272098A; Tue, 16 Oct 2018 19:40:22 +0000 (UTC) Date: Tue, 16 Oct 2018 15:40:21 -0400 From: Steven Rostedt To: Mathieu Desnoyers Cc: Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , linux-kernel , linux-api , Thomas Gleixner , Andy Lutomirski , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Chris Lameter , Ben Maurer , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , Sergey Senozhatsky Subject: Re: [RFC PATCH for 4.21 04/16] mm: Introduce vm_map_user_ram, vm_unmap_user_ram Message-ID: <20181016154021.429b3c08@gandalf.local.home> In-Reply-To: <1635827931.274.1539717691833.JavaMail.zimbra@efficios.com> References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com> <20181010191936.7495-5-mathieu.desnoyers@efficios.com> <20181016143016.10da89bd@gandalf.local.home> <1635827931.274.1539717691833.JavaMail.zimbra@efficios.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 16 Oct 2018 15:21:31 -0400 (EDT) Mathieu Desnoyers wrote: > ----- On Oct 16, 2018, at 2:30 PM, rostedt rostedt@goodmis.org wrote: > > > On Wed, 10 Oct 2018 15:19:24 -0400 > > Mathieu Desnoyers wrote: > > > >> + * vm_unmap_user_ram - unmap linear kernel address space set up by > >> vm_map_user_ram > >> + * @mem: the pointer returned by vm_map_user_ram > >> + * @count: the count passed to that vm_map_user_ram call (cannot unmap partial) > >> + */ > >> +void vm_unmap_user_ram(const void *mem, unsigned int count) > >> +{ > >> + unsigned long size = (unsigned long)count << PAGE_SHIFT; > >> + unsigned long addr = (unsigned long)mem; > >> + struct vmap_area *va; > >> + > >> + might_sleep(); > >> + BUG_ON(!addr); > >> + BUG_ON(addr < VMALLOC_START); > >> + BUG_ON(addr > VMALLOC_END); > >> + BUG_ON(!PAGE_ALIGNED(addr)); > >> + > >> + debug_check_no_locks_freed(mem, size); > >> + va = find_vmap_area(addr); > >> + BUG_ON(!va); > >> + free_unmap_vmap_area(va); > >> +} > >> +EXPORT_SYMBOL(vm_unmap_user_ram); > >> + > > > > Noticing this from Sergey's question in another patch, why are you > > using BUG_ON()? That's rather extreme and something we are trying to > > avoid adding more of (I still need to remove the BUG_ON()s I've added > > over ten years ago). I don't see why all these BUG_ON's can't be turned > > into: > > > > if (WARN_ON(x)) > > return; > > I borrowed the code from vm_unmap_ram(), which has the following checks: > > BUG_ON(!addr); > BUG_ON(addr < VMALLOC_START); > BUG_ON(addr > VMALLOC_END); > BUG_ON(!PAGE_ALIGNED(addr)); > [...] > va = find_vmap_area(addr); > BUG_ON(!va); > > The expectation here is that inputs to vm_unmap_ram() should always come from > vm_map_ram(), so an erroneous input is an internal kernel bug. I applied the > same logic to vm_unmap_user_ram() and vm_map_user_ram(). > > Should we turn all those BUG_ON() into if (WARN_ON(x)) return; in vm_{map,unmap}_ram > as well ? > > I would argue yes! That code was added in 2008 (which is also the same year I added BUG_ON() to my code). Back then it wasn't such an issue, but today we are finding (and Linus has been complaining) that BUG_ON really shouldn't be necessary. Especially if you can get out of the function with a simple return. -- Steve