Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas

From: Roman Penyaev <rpenyaev@suse.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Uladzislau Rezki <urezki@gmail.com>, Roman Gushchin <guro@fb.com>,
	Michal Hocko <mhocko@suse.com>,
	Matthew Wilcox <willy@infradead.org>,
	Thomas Garnier <thgarnie@google.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Joel Fernandes <joelaf@google.com>,
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
	Tejun Heo <tj@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Mike Rapoport <rppt@linux.ibm.com>, Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas
Date: Mon, 17 Jun 2019 16:50:17 +0200	[thread overview]
Message-ID: <fb05c3956eba18a8b01e8a8fa0396c7b@suse.de> (raw)
In-Reply-To: <CAK8P3a3sjuyeQBUprGFGCXUSDAJN_+c+2z=pCR5J05rByBVByQ@mail.gmail.com>

On 2019-06-17 16:44, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 4:12 PM Uladzislau Rezki <urezki@gmail.com> 
> wrote:
>> 
>> On Mon, Jun 17, 2019 at 02:14:11PM +0200, Arnd Bergmann wrote:
>> > gcc points out some obviously broken code in linux-next
>> >
>> > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
>> > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>> >     insert_vmap_area_augment(lva, &va->rb_node,
>> >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> >      &free_vmap_area_root, &free_vmap_area_list);
>> >      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> > mm/vmalloc.c:916:20: note: 'lva' was declared here
>> >   struct vmap_area *lva;
>> >                     ^~~
>> >
>> > Remove the obviously broken code. This is almost certainly
>> > not the correct solution, but it's what I have applied locally
>> > to get a clean build again.
>> >
>> > Please fix this properly.
>> >
> 
>> >
>> Please do not apply this. It will just break everything.
> 
> As I wrote in my description, this was purely meant as a bug
> report, not a patch to be applied.

That's a perfect way to attract attention! :)

> 
>> As Roman pointed we can just set lva = NULL; in the beginning to make 
>> GCC happy.
>> For some reason GCC decides that it can be used uninitialized, but 
>> that
>> is not true.
> 
> I got confused by the similarly named FL_FIT_TYPE/NE_FIT_TYPE

Names are indeed very confusing, that is true.  Very easy to mix up 
things.

--
Roman