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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e02e6116b08sm3739945276.13.2024.06.24.22.00.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jun 2024 22:00:26 -0700 (PDT) Date: Mon, 24 Jun 2024 22:00:24 -0700 (PDT) From: Hugh Dickins To: Andrew Morton cc: Barry Song <21cnbao@gmail.com>, Hugh Dickins , baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, ryan.roberts@arm.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yosryahmed@google.com, yuanshuai@oppo.com, yuzhao@google.com Subject: [PATCH mm-unstable] mm: folio_add_new_anon_rmap() careful __folio_set_swapbacked() Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit "mm: use folio_add_new_anon_rmap() if folio_test_anon(folio)=3D=3D false" has extended folio_add_new_anon_rmap() to use on non-exclusive folios, already visible to others in swap cache and on LRU. That renders its non-atomic __folio_set_swapbacked() unsafe: it risks overwriting concurrent atomic operations on folio->flags, losing bits added or restoring bits cleared. Since it's only used in this risky way when folio_test_locked and !folio_test_anon, many such races are excluded; but, for example, isolations by folio_test_clear_lru() are vulnerable, and setting or clearing active. It could just use the atomic folio_set_swapbacked(); but this function does try to avoid atomics where it can, so use a branch instead: just avoid setting swapbacked when it is already set, that is good enough. (Swapbacked is normally stable once set: lazyfree can undo it, but only later, when found anon in a page table.) This fixes a lot of instability under compaction and swapping loads: assorted "Bad page"s, VM_BUG_ON_FOLIO()s, apparently even page double frees - though I've not worked out what races could lead to the latter. Signed-off-by: Hugh Dickins Reviewed-by: David Hildenbrand --- mm/rmap.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index df1a43295c85..5394c1178bf1 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1408,7 +1408,9 @@ void folio_add_new_anon_rmap(struct folio *folio, str= uct vm_area_struct *vma, VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); VM_BUG_ON_VMA(address < vma->vm_start || address + (nr << PAGE_SHIFT) > vma->vm_end, vma); - __folio_set_swapbacked(folio); + + if (!folio_test_swapbacked(folio)) + __folio_set_swapbacked(folio); __folio_set_anon(folio, vma, address, exclusive); =20 if (likely(!folio_test_large(folio))) { --=20 2.35.3