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Date:   Mon, 17 Jun 2019 16:50:17 +0200
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
In-Reply-To: <CAK8P3a3sjuyeQBUprGFGCXUSDAJN_+c+2z=pCR5J05rByBVByQ@mail.gmail.com>
References: <20190617121427.77565-1-arnd@arndb.de>
 <20190617141244.5x22nrylw7hodafp@pc636>
 <CAK8P3a3sjuyeQBUprGFGCXUSDAJN_+c+2z=pCR5J05rByBVByQ@mail.gmail.com>
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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