From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753503AbeDSVT1 (ORCPT ); Thu, 19 Apr 2018 17:19:27 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:33242 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752725AbeDSVT0 (ORCPT ); Thu, 19 Apr 2018 17:19:26 -0400 Date: Thu, 19 Apr 2018 17:19:20 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Andrew Morton cc: David Miller , linux-mm@kvack.org, eric.dumazet@gmail.com, edumazet@google.com, bhutchings@solarflare.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com, virtualization@lists.linux-foundation.org, dm-devel@redhat.com, Vlastimil Babka Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM In-Reply-To: <20180419124751.8884e516e99825d83da3d87a@linux-foundation.org> Message-ID: References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <20180418.134651.2225112489265654270.davem@davemloft.net> <20180419124751.8884e516e99825d83da3d87a@linux-foundation.org> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 19 Apr 2018, Andrew Morton wrote: > On Thu, 19 Apr 2018 12:12:38 -0400 (EDT) Mikulas Patocka wrote: > > > The kvmalloc function tries to use kmalloc and falls back to vmalloc if > > kmalloc fails. > > > > Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then > > uses DMA-API on the returned memory or frees it with kfree. Such bugs were > > found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific > > code. > > > > These bugs are hard to reproduce because vmalloc falls back to kmalloc > > only if memory is fragmented. > > Yes, that's nasty. > > > In order to detect these bugs reliably I submit this patch that changes > > kvmalloc to always use vmalloc if CONFIG_DEBUG_VM is turned on. > > > > ... > > > > --- linux-2.6.orig/mm/util.c 2018-04-18 15:46:23.000000000 +0200 > > +++ linux-2.6/mm/util.c 2018-04-18 16:00:43.000000000 +0200 > > @@ -395,6 +395,7 @@ EXPORT_SYMBOL(vm_mmap); > > */ > > void *kvmalloc_node(size_t size, gfp_t flags, int node) > > { > > +#ifndef CONFIG_DEBUG_VM > > gfp_t kmalloc_flags = flags; > > void *ret; > > > > @@ -426,6 +427,7 @@ void *kvmalloc_node(size_t size, gfp_t f > > */ > > if (ret || size <= PAGE_SIZE) > > return ret; > > +#endif > > > > return __vmalloc_node_flags_caller(size, node, flags, > > __builtin_return_address(0)); > > Well, it doesn't have to be done at compile-time, does it? We could > add a knob (in debugfs, presumably) which enables this at runtime. > That's far more user-friendly. But who will turn it on in debugfs? It should be default for debugging kernels, so that users using them would report the error. Conditioning it on CONFIG_DEBUG_SG is better than CONFIG_DEBUG_VM, it will print a stacktrace where the incorrect use happened. Mikulas