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Mon, 14 Jul 2025 09:17:17 -0400 X-MC-Unique: wxL77xLTOK6D7_5OwZo9DA-1 X-Mimecast-MFC-AGG-ID: wxL77xLTOK6D7_5OwZo9DA_1752499036 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D0595180028A; Mon, 14 Jul 2025 13:17:15 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.80.96]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 2D21F1803AF2; Mon, 14 Jul 2025 13:17:14 +0000 (UTC) From: Luiz Capitulino To: david@redhat.com, willy@infradead.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, shivankg@amd.com, sj@kernel.org, harry.yoo@oracle.com Subject: [PATCH v3 4/4] fs: stable_page_flags(): use snapshot_page() Date: Mon, 14 Jul 2025 09:16:54 -0400 Message-ID: <52c16c0f00995a812a55980c2f26848a999a34ab.1752499009.git.luizcap@redhat.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Stat-Signature: kjckbwan8rg8n6uwopw37q7amkyju377 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6F1B540010 X-Rspam-User: X-HE-Tag: 1752499044-430935 X-HE-Meta: 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 SXfabJ0e GGgq5GLQyCx/7dpfLmPEqGF7oFFI3jInQjxur4wFrnu2f7IXHlp3iBaVV2+kVD3NPYY3mKje0Yh90sblF5vmw/WeYnUXygC0JEXD2c+Ptk4CgJRg= 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: A race condition is possible in stable_page_flags() where user-space is reading /proc/kpageflags concurrently to a folio split. This may lead to oopses or BUG_ON()s being triggered. To fix this, this commit uses snapshot_page() in stable_page_flags() so that stable_page_flags() works with a stable page and folio snapshots instead. Note that stable_page_flags() makes use of some functions that require the original page or folio pointer to work properly (eg. is_free_budy_page() and folio_test_idle()). Since those functions can't be used on the page snapshot, we replace their usage with flags that were set by snapshot_page() for this purpose. Signed-off-by: Luiz Capitulino --- fs/proc/page.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 936f8bbe5a6f..52e4f49c0638 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -147,6 +147,7 @@ static inline u64 kpf_copy_bit(u64 kflags, int ubit, int kbit) u64 stable_page_flags(const struct page *page) { const struct folio *folio; + struct page_snapshot ps; unsigned long k; unsigned long mapping; bool is_anon; @@ -158,7 +159,9 @@ u64 stable_page_flags(const struct page *page) */ if (!page) return 1 << KPF_NOPAGE; - folio = page_folio(page); + + snapshot_page(&ps, page); + folio = &ps.folio_snapshot; k = folio->flags; mapping = (unsigned long)folio->mapping; @@ -167,7 +170,7 @@ u64 stable_page_flags(const struct page *page) /* * pseudo flags for the well known (anonymous) memory mapped pages */ - if (page_mapped(page)) + if (folio_mapped(folio)) u |= 1 << KPF_MMAP; if (is_anon) { u |= 1 << KPF_ANON; @@ -179,7 +182,7 @@ u64 stable_page_flags(const struct page *page) * compound pages: export both head/tail info * they together define a compound page's start/end pos and order */ - if (page == &folio->page) + if (ps.idx == 0) u |= kpf_copy_bit(k, KPF_COMPOUND_HEAD, PG_head); else u |= 1 << KPF_COMPOUND_TAIL; @@ -189,25 +192,19 @@ u64 stable_page_flags(const struct page *page) folio_test_large_rmappable(folio)) { /* Note: we indicate any THPs here, not just PMD-sized ones */ u |= 1 << KPF_THP; - } else if (is_huge_zero_folio(folio)) { + } else if (is_huge_zero_pfn(ps.pfn)) { u |= 1 << KPF_ZERO_PAGE; u |= 1 << KPF_THP; - } else if (is_zero_folio(folio)) { + } else if (is_zero_pfn(ps.pfn)) { u |= 1 << KPF_ZERO_PAGE; } - /* - * Caveats on high order pages: PG_buddy and PG_slab will only be set - * on the head page. - */ - if (PageBuddy(page)) - u |= 1 << KPF_BUDDY; - else if (page_count(page) == 0 && is_free_buddy_page(page)) + if (ps.flags & PAGE_SNAPSHOT_PG_BUDDY) u |= 1 << KPF_BUDDY; - if (PageOffline(page)) + if (folio_test_offline(folio)) u |= 1 << KPF_OFFLINE; - if (PageTable(page)) + if (folio_test_pgtable(folio)) u |= 1 << KPF_PGTABLE; if (folio_test_slab(folio)) u |= 1 << KPF_SLAB; @@ -215,7 +212,7 @@ u64 stable_page_flags(const struct page *page) #if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT) u |= kpf_copy_bit(k, KPF_IDLE, PG_idle); #else - if (folio_test_idle(folio)) + if (ps.flags & PAGE_SNAPSHOT_PG_IDLE) u |= 1 << KPF_IDLE; #endif @@ -241,7 +238,7 @@ u64 stable_page_flags(const struct page *page) if (u & (1 << KPF_HUGE)) u |= kpf_copy_bit(k, KPF_HWPOISON, PG_hwpoison); else - u |= kpf_copy_bit(page->flags, KPF_HWPOISON, PG_hwpoison); + u |= kpf_copy_bit(ps.page_snapshot.flags, KPF_HWPOISON, PG_hwpoison); #endif u |= kpf_copy_bit(k, KPF_RESERVED, PG_reserved); -- 2.50.0