Re: [RFC PATCH 1/2] mm: introduce MAP_FIXED_SAFE

From: Florian Weimer <fweimer@redhat.com>
To: Michal Hocko <mhocko@kernel.org>, linux-api@vger.kernel.org
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH 1/2] mm: introduce MAP_FIXED_SAFE
Date: Fri, 17 Nov 2017 08:30:48 +0100	[thread overview]
Message-ID: <a3f7aed9-0df2-2fd6-cebb-ba569ad66781@redhat.com> (raw)
In-Reply-To: <20171116101900.13621-2-mhocko@kernel.org>

On 11/16/2017 11:18 AM, Michal Hocko wrote:
> +	if (flags & MAP_FIXED_SAFE) {
> +		struct vm_area_struct *vma = find_vma(mm, addr);
> +
> +		if (vma && vma->vm_start <= addr)
> +			return -ENOMEM;
> +	}

Could you pick a different error code which cannot also be caused by a 
an unrelated, possibly temporary condition?  Maybe EBUSY or EEXIST?

This would definitely help with application-based randomization of 
mappings, and there, actual ENOMEM and this error would have to be 
handled differently.

Thanks,
Florian