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From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
To: Peter Xu <peterx@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	linux-kernel@vger.kernel.org,
	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>,
	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 2/2] mm: prevent gup_fast from racing with COW during fork
Date: Tue, 3 Nov 2020 01:33:46 +0100
Message-ID: <20201103003346.GC52235@lx-t490> (raw)
In-Reply-To: <20201031152605.GD6357@xz-x1>

On Sat, Oct 31, 2020 at 11:26:05AM -0400, Peter Xu wrote:

...

> Shall we document this explicitly (if this patch still needs a repost)?

Yes, this patch series needs a v3 :)

> Seems not straightforward since that seems not the usual way to use seqcount,
> not sure whether I'm the only one that feels this way, though.

Yes, this usage is correct but not common. I've proposed a more explicit
comment above the write section code, in my reply to patch #2.

...

> The other thing is, considering this use of seqcount seems to be quite special
> as explained below, I'm just not sure whether this would confuse lockdep or
> kcsan, etc., if we decide to use write_seqcount_t_begin().
>

Lockdep won't be confused as it's not used in the raw_*() variant of the
seqcount APIs.

AFAIK KCSAN also has some margin to protect itself from this: see
seqlock.h KCSAN_SEQLOCK_REGION_MAX.

Thanks,

> Peter Xu

Ahmed Darwish
Linutronix GmbH

  reply index

Thread overview: 25+ 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
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 [this message]
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
2020-11-10 11:53                         ` Peter Zijlstra
2020-11-03 17:03         ` Peter Xu
2020-11-02 23:58   ` Ahmed S. Darwish

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