Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 20 Apr 2018 15:08:52 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     David Miller <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>, 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 <vbabka@suse.cz>
Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM
Message-ID: <20180420130852.GC16083@dhcp22.suse.cz>
References: <alpine.LRH.2.02.1804181029270.19294@file01.intranet.prod.int.rdu2.redhat.com>
 <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com>
 <alpine.LRH.2.02.1804181218270.19136@file01.intranet.prod.int.rdu2.redhat.com>
 <20180418.134651.2225112489265654270.davem@davemloft.net>
 <alpine.LRH.2.02.1804181350050.17942@file01.intranet.prod.int.rdu2.redhat.com>
 <alpine.LRH.2.02.1804191207380.31175@file01.intranet.prod.int.rdu2.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <alpine.LRH.2.02.1804191207380.31175@file01.intranet.prod.int.rdu2.redhat.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu 19-04-18 12:12:38, Mikulas Patocka wrote:
[...]
> From: Mikulas Patocka <mpatocka@redhat.com>
> 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 <mpatocka@redhat.com>

Nacked-by: Michal Hocko <mhocko@suse.com>

> ---
>  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