From: Oded Gabbay <ogabbay@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>, John Hubbard <jhubbard@nvidia.com>,
Leon Romanovsky <leonro@nvidia.com>,
Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Maya B . Gokhale" <gokhale2@llnl.gov>,
Yang Shi <yang.shi@linux.alibaba.com>,
Marty Mcfadden <mcfadden8@llnl.gov>,
Kirill Shutemov <kirill@shutemov.name>,
Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Christoph Hellwig <hch@lst.de>,
Andrew Morton <akpm@linux-foundation.org>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Xu <peterx@redhat.com>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification
Date: Wed, 16 Feb 2022 19:24:41 +0200 [thread overview]
Message-ID: <CAFCwf12KNkd43U8+hcfSL9RuT-T=7RrDExOK0eD4fe+3XiUrhw@mail.gmail.com> (raw)
In-Reply-To: <CAFCwf10eNmwq2wD71xjUhqkvv5+_pJMR1nPug2RqNDcFT4H86Q@mail.gmail.com>
On Wed, Feb 16, 2022 at 6:59 PM Oded Gabbay <oded.gabbay@gmail.com> wrote:
>
> On Mon, Sep 21, 2020 at 3:03 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Mon, Sep 21, 2020 at 10:35:05AM +0200, Jan Kara wrote:
> > > > My thinking is to hit this issue you have to already be doing
> > > > FOLL_LONGTERM, and if some driver hasn't been properly marked and
> > > > regresses, the fix is to mark it.
> > > >
> > > > Remember, this use case requires the pin to extend after a system
> > > > call, past another fork() system call, and still have data-coherence.
> > > >
> > > > IMHO that can only happen in the FOLL_LONGTERM case as it inhernetly
> > > > means the lifetime of the pin is being controlled by userspace, not by
> > > > the kernel. Otherwise userspace could not cause new DMA touches after
> > > > fork.
> > >
> > > I agree that the new aggressive COW behavior is probably causing issues
> > > only for FOLL_LONGTERM users. That being said it would be nice if even
> > > ordinary threaded FOLL_PIN users would not have to be that careful about
> > > fork(2) and possible data loss due to COW - we had certainly reports of
> > > O_DIRECT IO loosing data due to fork(2) and COW exactly because it is very
> > > subtle how it behaves... But as I wrote above this is not urgent since that
> > > problematic behavior exists since the beginning of O_DIRECT IO in Linux.
> >
> > Yes, I agree - what I was thinking is to do this FOLL_LONGTERM for the
> > rc and then a small patch to make it wider for the next cycle so it
> > can test in linux-next for a responsible time period.
> >
> > Interesting to hear you confirm block has also seen subtle user
> > problems with this as well.
> >
> > Jason
> >
>
> Hi Jason, Linus,
> Sorry for waking up this thread, but I've filed a bug against this change:
> https://bugzilla.kernel.org/show_bug.cgi?id=215616
>
> In the past week, I've bisected a problem we have in one of our new
> demos running on our Gaudi accelerator, and after a very long
> bisection, I've come to this commit.
> All the details are in the bug, but the bottom line is that somehow,
> this patch causes corruption when the numa balancing feature is
> enabled AND we don't use process affinity AND we use GUP to pin pages
> so our accelerator can DMA to/from system memory.
>
> Either disabling numa balancing, using process affinity to bind to
> specific numa-node or reverting this patch causes the bug to
> disappear.
> I validated the bug and the revert on kernels 5.9, 5.11 and 5.17-rc4.
>
> You can see our GUP code in the driver in get_user_memory() in
> drivers/misc/habanalabs/common/memory.c.
> It is fairly standard and I think I got that line from Daniel (cc'ed
> on this email).
>
> I would appreciate help from the mm experts here to understand how to
> fix this, but it looks as if this simplification caused or exposed
> some race between numa migration code and GUP.
>
> Thanks,
> Oded
Although I wrote it inside the bug, I just wanted to specify here the
exact commit id in the tree:
2020-09-04 - 09854ba94c6aad7886996bfbee2530b3d8a7f4f4 - mm:
do_wp_page() simplification <Linus Torvalds>
Thanks,
Oded
next prev parent reply other threads:[~2022-02-16 17:25 UTC|newest]
Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 23:49 [PATCH 0/4] mm: Simplfy cow handling Peter Xu
2020-08-21 23:49 ` [PATCH 1/4] mm: Trial do_wp_page() simplification Peter Xu
2020-08-24 8:36 ` Kirill Tkhai
2020-08-24 14:30 ` Jan Kara
2020-08-24 15:37 ` Kirill Tkhai
2020-08-24 18:22 ` Linus Torvalds
2020-09-01 7:01 ` Hugh Dickins
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 17:32 ` Linus Torvalds
2020-09-14 18:34 ` Peter Xu
2020-09-14 21:15 ` Peter Xu
2020-09-14 22:55 ` Jason Gunthorpe
2020-09-14 22:59 ` Linus Torvalds
2020-09-14 23:28 ` Jason Gunthorpe
2020-09-15 0:19 ` Linus Torvalds
2020-09-15 14:50 ` Peter Xu
2020-09-15 15:17 ` Peter Xu
2020-09-15 16:05 ` Jason Gunthorpe
2020-09-15 18:29 ` Jason Gunthorpe
2020-09-15 19:13 ` Peter Xu
2020-09-15 19:38 ` Jason Gunthorpe
2020-09-15 21:33 ` Peter Xu
2020-09-15 23:22 ` Jason Gunthorpe
2020-09-16 1:50 ` John Hubbard
2020-09-16 17:48 ` Jason Gunthorpe
2020-09-16 18:46 ` Peter Xu
2020-09-17 11:25 ` Jason Gunthorpe
2020-09-17 18:11 ` Linus Torvalds
2020-09-17 19:38 ` Jason Gunthorpe
2020-09-17 19:51 ` Linus Torvalds
2020-09-18 16:40 ` Peter Xu
2020-09-18 17:16 ` Linus Torvalds
2020-09-18 19:57 ` Peter Xu
2020-09-18 17:32 ` Jason Gunthorpe
2020-09-18 20:40 ` Peter Xu
2020-09-18 20:59 ` Linus Torvalds
2020-09-19 0:28 ` Jason Gunthorpe
2020-09-18 21:06 ` John Hubbard
2020-09-19 0:01 ` Jason Gunthorpe
2020-09-21 8:35 ` Jan Kara
2020-09-21 12:03 ` Jason Gunthorpe
2022-02-16 16:59 ` Oded Gabbay
2022-02-16 17:24 ` Oded Gabbay [this message]
2022-02-16 19:04 ` Linus Torvalds
2022-02-16 19:20 ` Oded Gabbay
2022-02-16 19:24 ` David Hildenbrand
2020-09-21 13:42 ` Michal Hocko
2020-09-21 14:18 ` Peter Xu
2020-09-21 14:28 ` Michal Hocko
2020-09-21 14:38 ` Tejun Heo
2020-09-21 14:43 ` Christian Brauner
2020-09-21 14:55 ` Michal Hocko
2020-09-21 15:04 ` Christian Brauner
2020-09-21 16:06 ` Michal Hocko
2020-09-23 7:53 ` Michal Hocko
2020-09-21 14:41 ` Christian Brauner
2020-09-21 14:57 ` Michal Hocko
2020-09-21 16:31 ` Peter Xu
2020-09-17 18:14 ` Peter Xu
2020-09-17 18:26 ` Linus Torvalds
2020-09-17 19:03 ` Peter Xu
2020-09-17 19:42 ` Linus Torvalds
2020-09-17 19:55 ` John Hubbard
2020-09-17 20:06 ` Jason Gunthorpe
2020-09-17 20:19 ` John Hubbard
2020-09-17 20:25 ` Jason Gunthorpe
2020-09-17 20:35 ` Linus Torvalds
2020-09-17 21:40 ` Peter Xu
2020-09-17 22:09 ` Jason Gunthorpe
2020-09-17 22:25 ` Linus Torvalds
2020-09-17 22:48 ` Ira Weiny
2020-09-18 9:36 ` Jan Kara
2020-09-18 9:44 ` Jan Kara
2020-09-18 16:19 ` Jason Gunthorpe
2020-09-15 10:23 ` Leon Romanovsky
2020-09-15 15:56 ` Jason Gunthorpe
2020-09-15 15:03 ` Oleg Nesterov
2020-09-15 16:18 ` Peter Xu
2020-08-21 23:49 ` [PATCH 2/4] mm/ksm: Remove reuse_ksm_page() Peter Xu
2020-08-21 23:49 ` [PATCH 3/4] mm/gup: Remove enfornced COW mechanism Peter Xu
2020-09-14 14:27 ` Oleg Nesterov
2020-09-14 17:59 ` Peter Xu
2020-09-14 19:03 ` Linus Torvalds
2020-08-21 23:49 ` [PATCH 4/4] mm: Add PGREUSE counter Peter Xu
2020-08-22 16:14 ` Linus Torvalds
2020-08-24 0:24 ` Peter Xu
2020-08-22 16:05 ` [PATCH 0/4] mm: Simplfy cow handling Linus Torvalds
2020-08-23 23:58 ` Peter Xu
2020-08-24 8:38 ` Kirill Tkhai
2020-08-27 14:15 ` Peter Xu
2021-02-02 14:40 [PATCH 1/4] mm: Trial do_wp_page() simplification Gal Pressman
2021-02-02 16:31 ` Peter Xu
2021-02-02 16:44 ` Jason Gunthorpe
2021-02-02 17:05 ` Peter Xu
2021-02-02 17:13 ` Jason Gunthorpe
2021-02-03 12:43 ` Gal Pressman
2021-02-03 14:00 ` Jason Gunthorpe
2021-02-03 14:47 ` Gal Pressman
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='CAFCwf12KNkd43U8+hcfSL9RuT-T=7RrDExOK0eD4fe+3XiUrhw@mail.gmail.com' \
--to=ogabbay@kernel.org \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=daniel.vetter@ffwll.ch \
--cc=gokhale2@llnl.gov \
--cc=gregkh@linuxfoundation.org \
--cc=hch@lst.de \
--cc=jack@suse.cz \
--cc=jannh@google.com \
--cc=jgg@ziepe.ca \
--cc=jhubbard@nvidia.com \
--cc=kirill@shutemov.name \
--cc=ktkhai@virtuozzo.com \
--cc=leonro@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mcfadden8@llnl.gov \
--cc=oleg@redhat.com \
--cc=peterx@redhat.com \
--cc=torvalds@linux-foundation.org \
--cc=yang.shi@linux.alibaba.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).