From: Jan Kara <jack@suse.cz>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jan Kara <jack@suse.cz>,
linux-kernel@vger.kernel.org, Peter Xu <peterx@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Christoph Hellwig <hch@lst.de>, Hugh Dickins <hughd@google.com>,
Jann Horn <jannh@google.com>, John Hubbard <jhubbard@nvidia.com>,
Kirill Shutemov <kirill@shutemov.name>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Leon Romanovsky <leonro@nvidia.com>,
Linux-MM <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork
Date: Mon, 2 Nov 2020 09:31:22 +0100 [thread overview]
Message-ID: <20201102083122.GA23988@quack2.suse.cz> (raw)
In-Reply-To: <20201030170226.GF2620339@nvidia.com>
On Fri 30-10-20 14:02:26, Jason Gunthorpe wrote:
> On Fri, Oct 30, 2020 at 05:51:05PM +0100, Jan Kara wrote:
> > > @@ -446,6 +447,12 @@ struct mm_struct {
> > > */
> > > atomic_t has_pinned;
> > >
> > > + /**
> > > + * @write_protect_seq: Odd when any thread is write protecting
> > > + * pages in this mm, for instance during fork().
> > > + */
> > > + seqcount_t write_protect_seq;
> > > +
> >
> > So this comment isn't quite true. We can be writeprotecting pages due to
> > many other reasons and not touch write_protect_seq. E.g. for shared
> > mappings or due to explicit mprotect() calls. So the write_protect_seq
> > protection has to be about something more than pure write protection. One
> > requirement certainly is that the VMA has to be is_cow_mapping(). What
> > about mprotect(2) calls? I guess the application would have only itself to
> > blame so we don't care?
>
> Yes, that sounds right, How about
>
> /**
> * @write_protect_seq: Locked when any thread is write protecting
> * pages for COW in this mm, for instance during page table copying
^^^ maybe I'd write a bit more explicitly "... write protecting
pages mapped by this mm to enforce later COW, ..."
> * for fork().
> */
>
> mprotect and shared mappings cause faults on write access not COW?
Correct.
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-11-02 8:31 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com>
2020-10-30 14:46 ` [PATCH v2 1/2] mm: reorganize internal_get_user_pages_fast() Jason Gunthorpe
2020-10-30 16:29 ` Jan Kara
2020-10-30 21:31 ` John Hubbard
2020-10-30 22:36 ` Peter Xu
2020-11-02 22:19 ` [PATCH v2 0/2] Add a seqcount between gup_fast and copy_page_range() Ahmed S. Darwish
2020-11-02 22:39 ` Linus Torvalds
2020-11-02 23:18 ` Ahmed S. Darwish
[not found] ` <2-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com>
2020-10-30 16:51 ` [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork Jan Kara
[not found] ` <20201030170226.GF2620339@nvidia.com>
2020-11-02 8:31 ` Jan Kara [this message]
2020-10-30 22:52 ` Peter Xu
[not found] ` <20201030235121.GQ2620339@nvidia.com>
2020-10-31 15:26 ` Peter Xu
2020-11-03 0:33 ` Ahmed S. Darwish
2020-11-03 0:17 ` Ahmed S. Darwish
[not found] ` <20201103002532.GL2620339@nvidia.com>
2020-11-03 0:41 ` Ahmed S. Darwish
2020-11-03 2:20 ` John Hubbard
2020-11-03 6:52 ` Ahmed S. Darwish
2020-11-03 17:40 ` Linus Torvalds
2020-11-04 1:32 ` Ahmed S. Darwish
2020-11-04 2:01 ` John Hubbard
2020-11-04 3:17 ` Ahmed S. Darwish
2020-11-04 18:38 ` Linus Torvalds
2020-11-04 19:54 ` Ahmed S. Darwish
2020-12-09 18:38 ` [tip: locking/core] seqlock: Prefix internal seqcount_t-only macros with a "do_" tip-bot2 for Ahmed S. Darwish
2020-12-09 18:38 ` [tip: locking/core] seqlock: kernel-doc: Specify when preemption is automatically altered tip-bot2 for Ahmed S. Darwish
2020-11-10 11:53 ` [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork Peter Zijlstra
2020-12-03 10:35 ` [tip: locking/core] seqlock: Rename __seqprop() users tip-bot2 for Peter Zijlstra
2020-11-03 17:03 ` [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork Peter Xu
2020-11-02 23:58 ` Ahmed S. Darwish
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