linux-kernel - Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm

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Date:   Mon, 17 Jun 2019 16:50:17 +0200
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Uladzislau Rezki <urezki@...il.com>, Roman Gushchin <guro@...com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG]: mm/vmalloc: uninitialized variable access in
 pcpu_get_vm_areas

On 2019-06-17 16:44, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 4:12 PM Uladzislau Rezki <urezki@...il.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