From: Jason Gunthorpe <jgg@nvidia.com>
To: <linux-kernel@vger.kernel.org>, Peter Xu <peterx@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: 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: [PATCH v2 0/2] Add a seqcount between gup_fast and copy_page_range()
Date: Fri, 30 Oct 2020 11:46:19 -0300 [thread overview]
Message-ID: <0-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> (raw)
As discussed and suggested by Linus use a seqcount to close the small race
between gup_fast and copy_page_range().
Unfortunately the good suggestion to just use write_seqcount_begin() blows
up lockdep immediately due to the (new?) requirement that the write side
of seqcount be in a preempt disabled region. For this application it does
not seem like a good idea, nor is it necessary as we don't spin on retry.
This is solved by being the first place to use raw_write_seqcount_t_begin()
This can go after the merge window. I was table 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.
v2:
- Use start not addr in lockless_pages_from_mm
- Replace unsigned long casts with using the proper variable type
- Update comments
- Use raw_write_seqcount_t_begin() instead of open coding
- Update commit messages
v1: https://lore.kernel.org/r/0-v1-281e425c752f+2df-gup_fork_jgg@nvidia.com
To: linux-kernel@vger.kernel.org
To: Peter Xu <peterx@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Linux-MM <linux-mm@kvack.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Kirill Shutemov <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jann Horn <jannh@google.com>
Jason Gunthorpe (2):
mm: reorganize internal_get_user_pages_fast()
mm: prevent gup_fast from racing with COW during fork
arch/x86/kernel/tboot.c | 1 +
drivers/firmware/efi/efi.c | 1 +
include/linux/mm_types.h | 7 +++
kernel/fork.c | 1 +
mm/gup.c | 118 +++++++++++++++++++++++--------------
mm/init-mm.c | 1 +
mm/memory.c | 10 +++-
7 files changed, 93 insertions(+), 46 deletions(-)
--
2.28.0
next reply other threads:[~2020-10-30 14:46 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-30 14:46 Jason Gunthorpe [this message]
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
2020-10-30 14:46 ` [PATCH v2 2/2] mm: prevent gup_fast from racing with COW during fork Jason Gunthorpe
2020-10-30 16:51 ` Jan Kara
2020-10-30 17:02 ` Jason Gunthorpe
2020-11-02 8:31 ` Jan Kara
2020-10-30 21:20 ` John Hubbard
2020-10-30 22:52 ` Peter Xu
2020-10-30 23:51 ` Jason Gunthorpe
2020-10-31 15:26 ` Peter Xu
2020-11-03 0:33 ` Ahmed S. Darwish
2020-11-03 0:17 ` Ahmed S. Darwish
2020-11-03 0:25 ` Jason Gunthorpe
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 7:05 ` John Hubbard
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
2020-11-10 11:53 ` Peter Zijlstra
2020-11-03 17:03 ` Peter Xu
2020-11-02 23:58 ` Ahmed S. Darwish
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
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