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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Peter Xu <peterx@redhat.com>,
	"Ahmed S. Darwish" <a.darwish@linutronix.de>,
	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>,
	Jan Kara <jack@suse.cz>, 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 v4 0/2] Add a seqcount between gup_fast and copy_page_range()
Date: Wed, 11 Nov 2020 10:27:29 -0800
Message-ID: <CAHk-=wizYDXb0Ej0JRdVJfguhGthmZMushJDT9MUezeX2jtvww@mail.gmail.com> (raw)
In-Reply-To: <0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com>

On Tue, Nov 10, 2020 at 3:44 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> As discussed and suggested by Linus use a seqcount to close the small race
> between gup_fast and copy_page_range().
>
> Ahmed confirms that raw_write_seqcount_begin() is the correct API to use
> in this case and it doesn't trigger any lockdeps.
>
> I was able to test it using two threads, one forking and the other using
> ibv_reg_mr() to trigger GUP fast. Modifying copy_page_range() to sleep
> made the window large enough to reliably hit to test the logic.

Looks all good to me.

             Linus

  parent reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com>
2020-11-10 23:44 ` [PATCH v4 1/2] mm: reorganize internal_get_user_pages_fast() Jason Gunthorpe
2020-11-11 18:27 ` Linus Torvalds [this message]
     [not found] ` <2-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com>
2020-11-11 19:59   ` [PATCH v4 2/2] mm: prevent gup_fast from racing with COW during fork Peter Xu
2020-11-12  7:41   ` Ahmed S. Darwish

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