From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754953AbeDTNIz (ORCPT ); Fri, 20 Apr 2018 09:08:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:49529 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754740AbeDTNIy (ORCPT ); Fri, 20 Apr 2018 09:08:54 -0400 Date: Fri, 20 Apr 2018 15:08:52 +0200 From: Michal Hocko To: Mikulas Patocka Cc: David Miller , Andrew Morton , 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 Message-ID: <20180420130852.GC16083@dhcp22.suse.cz> References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <20180418.134651.2225112489265654270.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 19-04-18 12:12:38, Mikulas Patocka wrote: [...] > From: Mikulas Patocka > Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM > > 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. > > 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. No way. This is just wrong! First of all, you will explode most likely on many allocations of small sizes. Second, CONFIG_DEBUG_VM tends to be enabled quite often. > Signed-off-by: Mikulas Patocka Nacked-by: Michal Hocko > --- > mm/util.c | 2 ++ > 1 file changed, 2 insertions(+) > > Index: linux-2.6/mm/util.c > =================================================================== > --- 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)); -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM Date: Fri, 20 Apr 2018 15:08:52 +0200 Message-ID: <20180420130852.GC16083@dhcp22.suse.cz> References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <20180418.134651.2225112489265654270.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: dm-devel@redhat.com, eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, edumazet@google.com, bhutchings@solarflare.com, Andrew Morton , David Miller , Vlastimil Babka To: Mikulas Patocka Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org On Thu 19-04-18 12:12:38, Mikulas Patocka wrote: [...] > From: Mikulas Patocka > Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM > > 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. > > 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. No way. This is just wrong! First of all, you will explode most likely on many allocations of small sizes. Second, CONFIG_DEBUG_VM tends to be enabled quite often. > Signed-off-by: Mikulas Patocka Nacked-by: Michal Hocko > --- > mm/util.c | 2 ++ > 1 file changed, 2 insertions(+) > > Index: linux-2.6/mm/util.c > =================================================================== > --- 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)); -- Michal Hocko SUSE Labs