From: Michal Hocko <mhocko@kernel.org>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Aaron Lu <aaron.lu@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] mm/mremap: Fail map duplication attempts for private mappings
Date: Thu, 20 Jul 2017 10:20:58 +0200 [thread overview]
Message-ID: <20170720082058.GF9058@dhcp22.suse.cz> (raw)
In-Reply-To: <fad64378-02d7-32c3-50c5-8b444a07d274@oracle.com>
On Wed 19-07-17 09:39:50, Mike Kravetz wrote:
> On 07/13/2017 12:11 PM, Vlastimil Babka wrote:
> > [+CC linux-api]
> >
> > On 07/13/2017 05:58 PM, Mike Kravetz wrote:
> >> mremap will create a 'duplicate' mapping if old_size == 0 is
> >> specified. Such duplicate mappings make no sense for private
> >> mappings. If duplication is attempted for a private mapping,
> >> mremap creates a separate private mapping unrelated to the
> >> original mapping and makes no modifications to the original.
> >> This is contrary to the purpose of mremap which should return
> >> a mapping which is in some way related to the original.
> >>
> >> Therefore, return EINVAL in the case where if an attempt is
> >> made to duplicate a private mapping.
> >>
> >> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> >
> > Acked-by: Vlastimil Babka <vbabka@suse.cz>
>
> After considering Michal's concerns with follow on patch, it appears
> this patch provides the most desired behavior. Any other concerns
> or issues with this patch?
Maybe we should add a pr_warn_once to make users aware that this is no
longer supported.
> If this moves forward, I will create man page updates to describe the
> mremap(old_size == 0) behavior.
>
> --
> Mike Kravetz
>
> >
> >> ---
> >> mm/mremap.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/mm/mremap.c b/mm/mremap.c
> >> index cd8a1b1..076f506 100644
> >> --- a/mm/mremap.c
> >> +++ b/mm/mremap.c
> >> @@ -383,6 +383,13 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> >> if (!vma || vma->vm_start > addr)
> >> return ERR_PTR(-EFAULT);
> >>
> >> + /*
> >> + * !old_len is a special case where a mapping is 'duplicated'.
> >> + * Do not allow this for private mappings.
Do not allow this for private mappings because we have never really
duplicated the range for those so the new VMA is a fresh one unrelated
to the original one which breaks mremap semantic. While we can do that
there doesn't seem to be any existing usecase currently.
> >> + */
> >> + if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
> >> + return ERR_PTR(-EINVAL);
> >> +
> >> if (is_vm_hugetlb_page(vma))
> >> return ERR_PTR(-EINVAL);
> >>
> >>
> >
--
Michal Hocko
SUSE Labs
--
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next prev parent reply other threads:[~2017-07-20 8:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1499961495-8063-1-git-send-email-mike.kravetz@oracle.com>
[not found] ` <1499961495-8063-1-git-send-email-mike.kravetz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-13 19:11 ` [PATCH] mm/mremap: Fail map duplication attempts for private mappings Vlastimil Babka
2017-07-13 22:33 ` Mike Kravetz
2017-07-14 4:51 ` Anshuman Khandual
[not found] ` <415625d2-1be9-71f0-ca11-a014cef98a3f-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-14 8:26 ` Michal Hocko
2017-07-14 17:29 ` Mike Kravetz
2017-07-17 6:44 ` Michal Hocko
2017-07-19 16:39 ` Mike Kravetz
2017-07-20 8:20 ` Michal Hocko [this message]
2017-07-20 20:37 ` [PATCH v2] " Mike Kravetz
2017-07-21 14:36 ` Michal Hocko
2017-07-21 21:18 ` Mike Kravetz
[not found] ` <cb9d9f6a-7095-582f-15a5-62643d65c736-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-24 8:50 ` Michal Hocko
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