From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 051086B0003 for ; Fri, 20 Apr 2018 09:08:56 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id h9so4238052pfn.22 for ; Fri, 20 Apr 2018 06:08:55 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z23si5111763pgc.484.2018.04.20.06.08.54 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 20 Apr 2018 06:08:54 -0700 (PDT) Date: Fri, 20 Apr 2018 15:08:52 +0200 From: Michal Hocko 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: Sender: owner-linux-mm@kvack.org List-ID: 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 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