From: Shakeel Butt <shakeelb@google.com>
To: Liam Howlett <liam.howlett@oracle.com>
Cc: Alistair Popple <apopple@nvidia.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"nouveau@lists.freedesktop.org" <nouveau@lists.freedesktop.org>,
"bskeggs@redhat.com" <bskeggs@redhat.com>,
"rcampbell@nvidia.com" <rcampbell@nvidia.com>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"jhubbard@nvidia.com" <jhubbard@nvidia.com>,
"bsingharora@gmail.com" <bsingharora@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"hch@infradead.org" <hch@infradead.org>,
"jglisse@redhat.com" <jglisse@redhat.com>,
"willy@infradead.org" <willy@infradead.org>,
"jgg@nvidia.com" <jgg@nvidia.com>,
"peterx@redhat.com" <peterx@redhat.com>,
"hughd@google.com" <hughd@google.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to_unmap
Date: Fri, 4 Jun 2021 17:41:03 -0700 [thread overview]
Message-ID: <CALvZod6myLUu0j13=nn2vCbH7kQJ4yXs06=0+pZYie2ZN13Mxw@mail.gmail.com> (raw)
In-Reply-To: <20210604204934.sbspsmwdqdtmz73d@revolver>
On Fri, Jun 4, 2021 at 1:49 PM Liam Howlett <liam.howlett@oracle.com> wrote:
>
> * Shakeel Butt <shakeelb@google.com> [210525 19:45]:
> > On Tue, May 25, 2021 at 11:40 AM Liam Howlett <liam.howlett@oracle.com> wrote:
> > >
> > [...]
> > > >
> > > > +/*
> > > > + * Walks the vma's mapping a page and mlocks the page if any locked vma's are
> > > > + * found. Once one is found the page is locked and the scan can be terminated.
> > > > + */
> > >
> > > Can you please add that this requires the mmap_sem() lock to the
> > > comments?
> > >
> >
> > Why does this require mmap_sem() lock? Also mmap_sem() lock of which mm_struct?
>
>
> Doesn't the mlock_vma_page() require the mmap_sem() for reading? The
> mm_struct in vma->vm_mm;
>
We are traversing all the vmas where this page is mapped of possibly
different mm_structs. I don't think we want to take mmap_sem() of all
those mm_structs. The commit b87537d9e2fe ("mm: rmap use pte lock not
mmap_sem to set PageMlocked") removed exactly that.
>
> From what I can see, at least the following paths have mmap_lock held
> for writing:
>
> munlock_vma_pages_range() from __do_munmap()
> munlokc_vma_pages_range() from remap_file_pages()
>
The following path does not hold mmap_sem:
exit_mmap() -> munlock_vma_pages_all() -> munlock_vma_pages_range().
I would really suggest all to carefully read the commit message of
b87537d9e2fe ("mm: rmap use pte lock not mmap_sem to set
PageMlocked").
Particularly the following paragraph:
...
Vlastimil Babka points out another race which this patch protects against.
try_to_unmap_one() might reach its mlock_vma_page() TestSetPageMlocked a
moment after munlock_vma_pages_all() did its Phase 1 TestClearPageMlocked:
leaving PageMlocked and unevictable when it should be evictable. mmap_sem
is ineffective because exit_mmap() does not hold it; page lock ineffective
because __munlock_pagevec() only takes it afterwards, in Phase 2; pte lock
is effective because __munlock_pagevec_fill() takes it to get the page,
after VM_LOCKED was cleared from vm_flags, so visible to try_to_unmap_one.
...
Alistair, please bring back the VM_LOCKED check with pte lock held and
the comment "Holding pte lock, we do *not* need mmap_lock here".
One positive outcome of this cleanup patch is the removal of
unnecessary invalidation (unmapping for kvm case) of secondary mmus.
next prev parent reply other threads:[~2021-06-05 0:42 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-24 13:27 [PATCH v9 00/10] Add support for SVM atomics in Nouveau Alistair Popple
2021-05-24 13:27 ` [PATCH v9 01/10] mm: Remove special swap entry functions Alistair Popple
2021-05-24 13:27 ` [PATCH v9 02/10] mm/swapops: Rework swap entry manipulation code Alistair Popple
2021-05-24 13:27 ` [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to_unmap Alistair Popple
2021-05-25 18:39 ` Liam Howlett
2021-05-25 23:45 ` Shakeel Butt
2021-06-04 20:49 ` Liam Howlett
2021-06-05 0:41 ` Shakeel Butt [this message]
2021-06-05 3:39 ` Liam Howlett
2021-06-05 4:19 ` Shakeel Butt
2021-06-07 4:51 ` Alistair Popple
2021-05-24 13:27 ` [PATCH v9 04/10] mm/rmap: Split migration into its own function Alistair Popple
2021-05-24 13:27 ` [PATCH v9 05/10] mm: Rename migrate_pgmap_owner Alistair Popple
2021-05-26 19:41 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 06/10] mm/memory.c: Allow different return codes for copy_nonpresent_pte() Alistair Popple
2021-05-26 19:50 ` Peter Xu
2021-05-27 1:20 ` Alistair Popple
2021-05-27 1:44 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 07/10] mm: Device exclusive memory access Alistair Popple
2021-05-24 22:11 ` Andrew Morton
2021-05-25 1:31 ` John Hubbard
2021-05-25 9:21 ` Alistair Popple
2021-05-25 11:51 ` Balbir Singh
2021-05-26 7:17 ` John Hubbard
2021-05-26 13:30 ` Alistair Popple
2021-06-02 8:50 ` Balbir Singh
2021-06-02 14:37 ` Peter Xu
2021-06-03 11:39 ` Alistair Popple
2021-06-03 14:47 ` Peter Xu
2021-06-04 1:07 ` Alistair Popple
2021-06-04 15:20 ` Peter Xu
2021-06-03 8:37 ` John Hubbard
2021-05-26 19:28 ` Peter Xu
2021-05-27 3:35 ` Alistair Popple
2021-05-27 13:04 ` Peter Xu
2021-05-28 1:48 ` Alistair Popple
2021-05-28 13:11 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 08/10] mm: Selftests for exclusive device memory Alistair Popple
2021-05-24 13:27 ` [PATCH v9 09/10] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-05-24 13:27 ` [PATCH v9 10/10] nouveau/svm: Implement atomic SVM access Alistair Popple
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