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Date: Mon, 24 Oct 2016 22:32:18 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andreas Gruenbacher <agruenba@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] shmem: avoid maybe-uninitialized warning
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On Mon 24-10-16 21:42:36, Arnd Bergmann wrote:
> On Monday, October 24, 2016 6:22:44 PM CEST Michal Hocko wrote:
> > On Mon 24-10-16 17:25:03, Arnd Bergmann wrote:
> > > After enabling -Wmaybe-uninitialized warnings, we get a false-postive
> > > warning for shmem:
> > > 
> > > mm/shmem.c: In function ‘shmem_getpage_gfp’:
> > > include/linux/spinlock.h:332:21: error: ‘info’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > 
> > Is this really a false positive? If we goto clear and then 
> >         if (sgp <= SGP_CACHE &&
> >             ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
> >                 if (alloced) {
> > 
> > we could really take a spinlock on an unitialized variable. But maybe
> > there is something that prevents from that...
> 
> I did the patch a few weeks ago (I sent the more important
> ones out first) and I think I concluded then that 'alloced'
> would be false in that case.

OK, I guess you are right and alloced is set only after info has been
already initialized. So this really looks like a false positive.

> 
> > Anyway the whole shmem_getpage_gfp is really hard to follow due to gotos
> > and labels proliferation.
> 
> Exactly. Maybe we should mark the patch for -stable backports after all
> just to be sure.

I am not really sure a stable backport is really necessary but a cleanup
in this area would be more than welcome. At least from me ;)
-- 
Michal Hocko
SUSE Labs