From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: JianKang Chen <chenjiankang1@huawei.com>,
mgorman@techsingularity.net, hannes@cmpxchg.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
xieyisheng1@huawei.com, guohanjun@huawei.com,
wangkefeng.wang@huawei.com
Subject: Re: [PATCH resend] mm/page_alloc: fix comment is __get_free_pages
Date: Thu, 14 Dec 2017 15:06:08 +0100 [thread overview]
Message-ID: <20171214140608.GQ16951@dhcp22.suse.cz> (raw)
In-Reply-To: <20171201111845.iyoua7hhjodpuvoy@dhcp22.suse.cz>
On Fri 01-12-17 12:18:45, Michal Hocko wrote:
> On Fri 01-12-17 08:24:14, Michal Hocko wrote:
> > On Thu 30-11-17 13:17:06, Andrew Morton wrote:
> > > On Thu, 30 Nov 2017 07:53:35 +0100 Michal Hocko <mhocko@kernel.org> wrote:
> > >
> > > > > mm... So we have a caller which hopes to be getting highmem pages but
> > > > > isn't. Caller then proceeds to pointlessly kmap the page and wonders
> > > > > why it isn't getting as much memory as it would like on 32-bit systems,
> > > > > etc.
> > > >
> > > > How he can kmap the page when he gets a _virtual_ address?
> > >
> > > doh.
> > >
> > > > > I do think we should help ferret out such bogosity. A WARN_ON_ONCE
> > > > > would suffice.
> > > >
> > > > This function has always been about lowmem pages. I seriously doubt we
> > > > have anybody confused and asking for a highmem page in the kernel. I
> > > > haven't checked that but it would already blow up as VM_BUG_ON tends to
> > > > be enabled on many setups.
> > >
> > > OK. But silently accepting __GFP_HIGHMEM is a bit weird - callers
> > > shouldn't be doing that in the first place.
> >
> > Yes, they shouldn't be.
> >
> > > I wonder what happens if we just remove the WARN_ON and pass any
> > > __GFP_HIGHMEM straight through. The caller gets a weird address from
> > > page_to_virt(highmem page) and usually goes splat? Good enough
> > > treatment for something which never happens anyway?
> >
> > page_address will return NULL so they will blow up and leak the freshly
> > allocated memory.
>
> let me be more specific. They will blow up and leak if the returned
> address is not checked. If it is then we just leak. None of that sounds
> good to me.
So do we care and I will resend the patch in that case or I just drop
this from my patch queue?
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-12-14 14:06 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-27 11:09 [PATCH resend] mm/page_alloc: fix comment is __get_free_pages JianKang Chen
2017-11-27 11:33 ` Michal Hocko
2017-11-29 16:04 ` Michal Hocko
2017-11-29 21:41 ` Andrew Morton
2017-11-30 6:53 ` Michal Hocko
2017-11-30 21:17 ` Andrew Morton
2017-12-01 7:24 ` Michal Hocko
2017-12-01 11:18 ` Michal Hocko
2017-12-14 14:06 ` Michal Hocko [this message]
2017-12-14 20:33 ` Andrew Morton
2017-12-15 9:36 ` Michal Hocko
2017-12-15 20:57 ` Andrew Morton
2017-12-16 11:52 ` Michal Hocko
2018-04-06 10:02 ` Michal Hocko
2018-04-06 19:58 ` Andrew Morton
-- strict thread matches above, loose matches on Subject: below --
2017-11-25 7:20 JianKang Chen
2017-11-27 6:22 ` Anshuman Khandual
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