From: Mikulas Patocka <mpatocka@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>,
Vlastimil Babka <vbabka@suse.cz>, Peter Xu <peterx@redhat.com>,
stable <stable@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jann Horn <jannh@google.com>, Kirill Tkhai <ktkhai@virtuozzo.com>,
Shaohua Li <shli@fb.com>, Nadav Amit <namit@vmware.com>,
Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Android Kernel Team <kernel-team@android.com>,
Andrea Arcangeli <aarcange@redhat.com>,
David Hildenbrand <david@redhat.com>,
Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH 0/5] 4.14 backports of fixes for "CoW after fork() issue"
Date: Wed, 7 Apr 2021 14:47:14 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.2104071432420.31819@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <CAHk-=wj0JH6PnG7dW51Sr5ZqhomqSaSLTQV7z4Si2dLeSVcO_g@mail.gmail.com>
On Wed, 7 Apr 2021, Linus Torvalds wrote:
> On Wed, Apr 7, 2021 at 9:33 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > Trying my hand at backporting the patchsets Peter mentioned proved
> > this to be far from easy with many dependencies. Let me look into
> > Vlastimil's suggestion to backport only 17839856fd58 and it sounds
> > like 5.4 already followed that path.
>
> Well, in many ways 17839856fd58 was the "simple and obvious" fix, and
> I do think it's easily backportable.
>
> But it *did* cause problems too. Those problems may not be issues on
> those old kernels, though.
>
> In particular, commit 17839856fd58 caused uffd-wp to stop working
> right, and it caused some issues with debugging (I forget the exact
> details, but I think it was strace accessing PROT_NONE or write-only
> pages or something like that, and COW failed).
>
> But yes, in many ways that commit is a much simpler and more
> straightforward one (which is why I tried it once - we ended up with
> the much more subtle and far-reaching fixes after the UFFD issues
> crept up).
>
> The issues that 17839856fd58 caused may be entire non-events in old
> kernels. In fact, the uffd writeprotect API was added fairly recently
> (see commit 63b2d4174c4a that made it into v5.7), so the uffd-wp issue
> that was triggered probably cannot happen in the old kernels.
>
> The strace issue might not be relevant either, but I forget what the
> details were. Mikilas should know.
>
> See
>
> https://lore.kernel.org/lkml/alpine.LRH.2.02.2009031328040.6929@file01.intranet.prod.int.rdu2.redhat.com/
>
> for Mikulas report. I never looked into it in detail, because by then
> the uffd-wp issue had already come up, so it was juat another nail in
> the coffin for that simpler approach.
>
> Mikulas, do you remember?
>
> Linus
Hi
I think that we never found a root cause for this bug. I was testing if
the whole system can run from persistent memory and found out that strace
didn't work. I bisected it, reported it and when I received Peter Xu's
patches (which fixed it), I stopped bothering about it.
So, we fixed it, but we don't know why.
Peter Xu's patchset that fixed it is here:
https://lore.kernel.org/lkml/20200821234958.7896-1-peterx@redhat.com/
Mikulas
next prev parent reply other threads:[~2021-04-07 18:47 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 18:17 [PATCH 0/5] 4.14 backports of fixes for "CoW after fork() issue" Suren Baghdasaryan
2021-04-01 18:17 ` [PATCH 1/5] mm: reuse only-pte-mapped KSM page in do_wp_page() Suren Baghdasaryan
2021-04-01 19:38 ` Greg KH
2021-04-01 19:47 ` Suren Baghdasaryan
2021-04-01 18:17 ` [PATCH 2/5] mm: do_wp_page() simplification Suren Baghdasaryan
2021-04-01 18:17 ` [PATCH 3/5] mm: fix misplaced unlock_page in do_wp_page() Suren Baghdasaryan
2021-04-01 18:17 ` [PATCH 4/5] userfaultfd: wp: add helper for writeprotect check Suren Baghdasaryan
2021-04-01 18:17 ` [PATCH 5/5] mm/userfaultfd: fix memory corruption due to writeprotect Suren Baghdasaryan
2021-04-01 18:59 ` [PATCH 0/5] 4.14 backports of fixes for "CoW after fork() issue" Linus Torvalds
2021-04-01 19:43 ` Suren Baghdasaryan
2021-04-01 23:47 ` Peter Xu
2021-04-02 0:12 ` Suren Baghdasaryan
2021-04-07 13:21 ` Vlastimil Babka
2021-04-07 14:30 ` Peter Xu
2021-04-07 16:07 ` Linus Torvalds
2021-04-07 16:33 ` Suren Baghdasaryan
2021-04-07 17:04 ` Linus Torvalds
2021-04-07 18:47 ` Mikulas Patocka [this message]
2021-04-07 19:22 ` Linus Torvalds
2021-04-07 21:53 ` Suren Baghdasaryan
2021-04-21 20:01 ` Suren Baghdasaryan
2021-04-21 21:05 ` Peter Xu
2021-04-21 21:17 ` Suren Baghdasaryan
2021-04-21 23:01 ` Suren Baghdasaryan
2021-04-21 22:59 ` Vlastimil Babka
2021-04-21 23:05 ` Suren Baghdasaryan
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=alpine.LRH.2.02.2104071432420.31819@file01.intranet.prod.int.rdu2.redhat.com \
--to=mpatocka@redhat.com \
--cc=aarcange@redhat.com \
--cc=david@redhat.com \
--cc=gregkh@linuxfoundation.org \
--cc=jannh@google.com \
--cc=jgg@ziepe.ca \
--cc=kernel-team@android.com \
--cc=ktkhai@virtuozzo.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=namit@vmware.com \
--cc=peterx@redhat.com \
--cc=shli@fb.com \
--cc=stable@vger.kernel.org \
--cc=surenb@google.com \
--cc=torvalds@linux-foundation.org \
--cc=vbabka@suse.cz \
/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).