linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Peter Xu <peterx@redhat.com>, Nadav Amit <namit@vmware.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Minchan Kim <minchan@kernel.org>, Colin Cross <ccross@google.com>,
	Suren Baghdasarya <surenb@google.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH 1/8] mm/madvise: propagate vma->vm_end changes
Date: Mon, 27 Sep 2021 12:08:52 +0300	[thread overview]
Message-ID: <20210927090852.sc5u65ufwvfx57rl@box.shutemov.name> (raw)
In-Reply-To: <20210926161259.238054-2-namit@vmware.com>

On Sun, Sep 26, 2021 at 09:12:52AM -0700, Nadav Amit wrote:
> From: Nadav Amit <namit@vmware.com>
> 
> The comment in madvise_dontneed_free() says that vma splits that occur
> while the mmap-lock is dropped, during userfaultfd_remove(), should be
> handled correctly, but nothing in the code indicates that it is so: prev
> is invalidated, and do_madvise() will therefore continue to update VMAs
> from the "obsolete" end (i.e., the one before the split).
> 
> Propagate the changes to end from madvise_dontneed_free() back to
> do_madvise() and continue the updates from the new end accordingly.

Could you describe in details a race that would lead to wrong behaviour?

If mmap lock was dropped any change to VMA layout can appear. We can have
totally unrelated VMA there.

Either way, if userspace change VMA layout for a region that is under
madvise(MADV_DONTNEED) it is totally broken. I don't see a valid reason to
do this.

The current behaviour looks reasonable to me. Yes, we can miss VMAs, but
these VMAs can also be created just after madvise() is finished.

-- 
 Kirill A. Shutemov


  reply	other threads:[~2021-09-27  9:08 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-26 16:12 [RFC PATCH 0/8] mm/madvise: support process_madvise(MADV_DONTNEED) Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 1/8] mm/madvise: propagate vma->vm_end changes Nadav Amit
2021-09-27  9:08   ` Kirill A. Shutemov [this message]
2021-09-27 10:11     ` Nadav Amit
2021-09-27 11:55       ` Kirill A. Shutemov
2021-09-27 12:33         ` Nadav Amit
2021-09-27 12:45           ` Kirill A. Shutemov
2021-09-27 12:59             ` Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 2/8] mm/madvise: remove unnecessary check on madvise_dontneed_free() Nadav Amit
2021-09-27  9:11   ` Kirill A. Shutemov
2021-09-27 11:05     ` Nadav Amit
2021-09-27 12:19       ` Kirill A. Shutemov
2021-09-27 12:52         ` Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 3/8] mm/madvise: remove unnecessary checks on madvise_free_single_vma() Nadav Amit
2021-09-27  9:17   ` Kirill A. Shutemov
2021-09-27  9:24     ` Kirill A. Shutemov
2021-09-26 16:12 ` [RFC PATCH 4/8] mm/madvise: define madvise behavior in a struct Nadav Amit
2021-09-27  9:31   ` Kirill A. Shutemov
2021-09-27 10:31     ` Nadav Amit
2021-09-27 12:14       ` Kirill A. Shutemov
2021-09-27 20:36         ` Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 5/8] mm/madvise: perform certain operations once on process_madvise() Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 6/8] mm/madvise: more aggressive TLB batching Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 7/8] mm/madvise: deduplicate code in madvise_dontneed_free() Nadav Amit
2021-09-26 16:12 ` [RFC PATCH 8/8] mm/madvise: process_madvise(MADV_DONTNEED) Nadav Amit
2021-09-27  9:24 ` [RFC PATCH 0/8] mm/madvise: support process_madvise(MADV_DONTNEED) David Hildenbrand
2021-09-27 10:41   ` Nadav Amit
2021-09-27 10:58     ` David Hildenbrand
2021-09-27 12:00       ` Nadav Amit
2021-09-27 12:16         ` Michal Hocko
2021-09-27 19:12           ` Nadav Amit
2021-09-29  7:52             ` Michal Hocko
2021-09-29 18:31               ` Nadav Amit
2021-10-12 23:14                 ` Peter Xu
2021-10-13 15:47                   ` Nadav Amit
2021-10-13 23:09                     ` Peter Xu
2021-09-27 17:05         ` David Hildenbrand
2021-09-27 19:59           ` Nadav Amit
2021-09-28  8:53             ` David Hildenbrand
2021-09-28 22:56               ` Nadav Amit
2021-10-04 17:58                 ` David Hildenbrand
2021-10-07 16:19                   ` Nadav Amit
2021-10-07 16:46                     ` David Hildenbrand

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210927090852.sc5u65ufwvfx57rl@box.shutemov.name \
    --to=kirill@shutemov.name \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=ccross@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=minchan@kernel.org \
    --cc=nadav.amit@gmail.com \
    --cc=namit@vmware.com \
    --cc=peterx@redhat.com \
    --cc=rppt@linux.vnet.ibm.com \
    --cc=surenb@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).