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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Ahmed S. Darwish" <a.darwish@linutronix.de>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Peter Xu <peterx@redhat.com>,
	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>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sebastian Siewior <bigeasy@linutronix.de>
Subject: Re: [PATCH v2 0/2] Add a seqcount between gup_fast and copy_page_range()
Date: Mon, 2 Nov 2020 14:39:49 -0800
Message-ID: <CAHk-=wj2jtBhfgpxCkgXcyOPn3YFFWeJ-vHsppocBjdFQ2F6Og@mail.gmail.com> (raw)
In-Reply-To: <20201102221945.GA48454@lx-t490>

On Mon, Nov 2, 2020 at 2:19 PM Ahmed S. Darwish <a.darwish@linutronix.de> wrote:
>
> Disabling preemption for seqcount_t write-side critical sections was
> never a new requirement. It has always been this way, for the reasons
> explained at Documentation/locking/seqlock.rst, "Introduction" section.

Note that that is only true if you spin on the reading side (either of
the two kinds of spinning: (a) spinning to wait for it to become even,
or (b) repeating if they don't match)

Which this code doesn't do, it just fails.

I'm not sure how to perhaps document that.

             Linus

  reply index

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 [this message]
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
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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