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Subject: Re: [PATCH 02/18] mm: make vm_mmap killable
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From: Vlastimil Babka <vbabka@suse.cz>
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Date: Fri, 11 Mar 2016 13:43:41 +0100
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To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Alex Deucher <alexander.deucher@amd.com>, Alex Thorlton <athorlton@sgi.com>, Andrea Arcangeli <aarcange@redhat.com>, Andy Lutomirski <luto@amacapital.net>, Benjamin LaHaise <bcrl@kvack.org>, =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>, Daniel Vetter <daniel.vetter@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, David Airlie <airlied@linux.ie>, Davidlohr Bueso <dave@stgolabs.net>, David Rientjes <rientjes@google.com>, "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Konstantin Khlebnikov <koct9i@gmail.com>, linux-arch@vger.kernel.org, Mel Gorman <mgorman@suse.de>, Oleg Nesterov <oleg@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Petr Cermak <petrcermak@chromium.org>, Thomas Gleixner <tglx@linutronix.de>, Al Viro <viro@zeniv.linux.org.uk>
Message-ID: <20160311124341.pQhh_wXiiF2LpMW71S5YzraOWSXpHt7z6HxdSxJ94z4@z>

On 03/11/2016 01:12 PM, Michal Hocko wrote:
> On Fri 11-03-16 10:59:30, Vlastimil Babka wrote:
>> On 02/29/2016 02:26 PM, Michal Hocko wrote:
>> >From: Michal Hocko <mhocko@suse.com>
>> >
>> >All the callers of vm_mmap seem to check for the failure already
>> >and bail out in one way or another on the error which means that
>>
>> Hmm I'm not that sure about this one:
>>   17   1071  fs/binfmt_elf.c <<load_elf_binary>>
>>
>> Assigns result of vm_mmap() to "error" variable which is never checked.
>
> Yes it is not checked but not used either. If the current got killed
> then it wouldn't return to the userspace so my understanding is that not
> checking this value is not a problem. At least that is my understanding.

Hmm, that's true. So,

Acked-by: Vlastimil Babka <vbabka@suse.cz>

>> Shouldn't __must_check trigger here?
>
> well, __must_check is a misleading name. It doesn't actually enforce the
> value is checked. It just has to be used and an assignment is
> sufficient. I was discussing this without our gcc guy and he promissed
> to look and try to come up with a different attribute which would
> actually work like __must_check.

OK!