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Tue, 9 Apr 2024 19:23:32 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, David Hildenbrand , Andrew Morton , "Matthew Wilcox (Oracle)" , Peter Xu , Ryan Roberts , Yin Fengwei , Yang Shi , Zi Yan , Jonathan Corbet , Hugh Dickins , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Chris Zankel , Max Filippov , Muchun Song , Miaohe Lin , Naoya Horiguchi , Richard Chang Subject: [PATCH v1 01/18] mm: allow for detecting underflows with page_mapcount() again Date: Tue, 9 Apr 2024 21:22:44 +0200 Message-ID: <20240409192301.907377-2-david@redhat.com> In-Reply-To: <20240409192301.907377-1-david@redhat.com> References: <20240409192301.907377-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 X-Rspamd-Queue-Id: 6983D20018 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: uehjkd4eef9wfeqn67ayf8f3cphyhw9r X-HE-Tag: 1712690650-217079 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Commit 53277bcf126d ("mm: support page_mapcount() on page_has_type() pages") made it impossible to detect mapcount underflows by treating any negative raw mapcount value as a mapcount of 0. We perform such underflow checks in zap_present_folio_ptes() and zap_huge_pmd(), which would currently no longer trigger. Let's check against PAGE_MAPCOUNT_RESERVE instead by using page_type_has_type(), like page_has_type() would, so we can still catch some underflows. Fixes: 53277bcf126d ("mm: support page_mapcount() on page_has_type() pages") Signed-off-by: David Hildenbrand --- include/linux/mm.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index ef34cf54c14f..0fb8a40f82dd 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1229,11 +1229,10 @@ static inline void page_mapcount_reset(struct page *page) */ static inline int page_mapcount(struct page *page) { - int mapcount = atomic_read(&page->_mapcount) + 1; + int mapcount = atomic_read(&page->_mapcount); /* Handle page_has_type() pages */ - if (mapcount < 0) - mapcount = 0; + mapcount = page_type_has_type(mapcount) ? 0 : mapcount + 1; if (unlikely(PageCompound(page))) mapcount += folio_entire_mapcount(page_folio(page));