From: Suren Baghdasaryan <surenb@google.com>
To: akpm@linux-foundation.org
Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org,
aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com,
david@redhat.com, ryan.roberts@arm.com, hughd@google.com,
mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org,
willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com,
zhangpeng362@huawei.com, bgeffon@google.com,
kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com,
surenb@google.com, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, kernel-team@android.com
Subject: [PATCH v6 1/5] mm/rmap: support move to different root anon_vma in folio_move_anon_rmap()
Date: Wed, 6 Dec 2023 02:36:55 -0800 [thread overview]
Message-ID: <20231206103702.3873743-2-surenb@google.com> (raw)
In-Reply-To: <20231206103702.3873743-1-surenb@google.com>
From: Andrea Arcangeli <aarcange@redhat.com>
For now, folio_move_anon_rmap() was only used to move a folio to a
different anon_vma after fork(), whereby the root anon_vma stayed
unchanged. For that, it was sufficient to hold the folio lock when
calling folio_move_anon_rmap().
However, we want to make use of folio_move_anon_rmap() to move folios
between VMAs that have a different root anon_vma. As folio_referenced()
performs an RMAP walk without holding the folio lock but only holding the
anon_vma in read mode, holding the folio lock is insufficient.
When moving to an anon_vma with a different root anon_vma, we'll have to
hold both, the folio lock and the anon_vma lock in write mode.
Consequently, whenever we succeeded in folio_lock_anon_vma_read() to
read-lock the anon_vma, we have to re-check if the mapping was changed
in the meantime. If that was the case, we have to retry.
Note that folio_move_anon_rmap() must only be called if the anon page is
exclusive to a process, and must not be called on KSM folios.
This is a preparation for UFFDIO_MOVE, which will hold the folio lock,
the anon_vma lock in write mode, and the mmap_lock in read mode.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
---
mm/rmap.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/mm/rmap.c b/mm/rmap.c
index 7a27a2b41802..525c5bc0b0b3 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -542,6 +542,7 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
struct anon_vma *root_anon_vma;
unsigned long anon_mapping;
+retry:
rcu_read_lock();
anon_mapping = (unsigned long)READ_ONCE(folio->mapping);
if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
@@ -552,6 +553,17 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
root_anon_vma = READ_ONCE(anon_vma->root);
if (down_read_trylock(&root_anon_vma->rwsem)) {
+ /*
+ * folio_move_anon_rmap() might have changed the anon_vma as we
+ * might not hold the folio lock here.
+ */
+ if (unlikely((unsigned long)READ_ONCE(folio->mapping) !=
+ anon_mapping)) {
+ up_read(&root_anon_vma->rwsem);
+ rcu_read_unlock();
+ goto retry;
+ }
+
/*
* If the folio is still mapped, then this anon_vma is still
* its anon_vma, and holding the mutex ensures that it will
@@ -586,6 +598,18 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio,
rcu_read_unlock();
anon_vma_lock_read(anon_vma);
+ /*
+ * folio_move_anon_rmap() might have changed the anon_vma as we might
+ * not hold the folio lock here.
+ */
+ if (unlikely((unsigned long)READ_ONCE(folio->mapping) !=
+ anon_mapping)) {
+ anon_vma_unlock_read(anon_vma);
+ put_anon_vma(anon_vma);
+ anon_vma = NULL;
+ goto retry;
+ }
+
if (atomic_dec_and_test(&anon_vma->refcount)) {
/*
* Oops, we held the last refcount, release the lock
--
2.43.0.rc2.451.g8631bc7472-goog
next prev parent reply other threads:[~2023-12-06 10:37 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-06 10:36 [PATCH v6 0/5] userfaultfd move option Suren Baghdasaryan
2023-12-06 10:36 ` Suren Baghdasaryan [this message]
2023-12-06 10:36 ` [PATCH v6 2/5] userfaultfd: UFFDIO_MOVE uABI Suren Baghdasaryan
2023-12-06 10:36 ` [PATCH v6 3/5] selftests/mm: call uffd_test_ctx_clear at the end of the test Suren Baghdasaryan
2023-12-06 10:36 ` [PATCH v6 4/5] selftests/mm: add uffd_test_case_ops to allow test case-specific operations Suren Baghdasaryan
2023-12-06 10:36 ` [PATCH v6 5/5] selftests/mm: add UFFDIO_MOVE ioctl test Suren Baghdasaryan
2023-12-10 14:23 ` Mark Brown
2023-12-11 1:01 ` Suren Baghdasaryan
2023-12-11 3:04 ` Suren Baghdasaryan
2023-12-11 11:15 ` Mark Brown
2023-12-11 12:03 ` David Hildenbrand
2023-12-11 12:24 ` Mark Brown
2023-12-11 16:15 ` Suren Baghdasaryan
2023-12-11 16:25 ` Mark Brown
2023-12-11 16:29 ` Suren Baghdasaryan
2023-12-11 16:34 ` Mark Brown
2023-12-11 16:43 ` Suren Baghdasaryan
2023-12-11 16:32 ` David Hildenbrand
2023-12-11 16:41 ` Mark Brown
2023-12-11 16:53 ` David Hildenbrand
2023-12-11 17:32 ` Mark Brown
2023-12-11 18:00 ` David Hildenbrand
2023-12-11 20:01 ` Mark Brown
2023-12-11 20:11 ` John Hubbard
2023-12-12 15:27 ` David Hildenbrand
2023-12-12 19:39 ` Mark Brown
2023-12-11 18:46 ` John Hubbard
2023-12-11 20:21 ` Mark Brown
2023-12-11 20:29 ` John Hubbard
2023-12-12 15:12 ` Mark Brown
2023-12-13 2:14 ` John Hubbard
2023-12-13 3:58 ` Muhammad Usama Anjum
2023-12-13 5:52 ` John Hubbard
2023-12-13 5:55 ` John Hubbard
2023-12-13 9:59 ` David Hildenbrand
2023-12-13 22:01 ` John Hubbard
2023-12-14 9:02 ` David Hildenbrand
2023-12-13 14:00 ` Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20231206103702.3873743-2-surenb@google.com \
--to=surenb@google.com \
--cc=Liam.Howlett@oracle.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=axelrasmussen@google.com \
--cc=bgeffon@google.com \
--cc=brauner@kernel.org \
--cc=david@redhat.com \
--cc=hughd@google.com \
--cc=jannh@google.com \
--cc=jdduke@google.com \
--cc=kaleshsingh@google.com \
--cc=kernel-team@android.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lokeshgidra@google.com \
--cc=mhocko@suse.com \
--cc=ngeoffray@google.com \
--cc=peterx@redhat.com \
--cc=rppt@kernel.org \
--cc=ryan.roberts@arm.com \
--cc=shuah@kernel.org \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
--cc=zhangpeng362@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).