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Thu, 26 Jun 2025 14:17:19 -0400 X-MC-Unique: 7UNU5ohPMiy7mflE6UnpEg-1 X-Mimecast-MFC-AGG-ID: 7UNU5ohPMiy7mflE6UnpEg_1750961838 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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 A1DEE180028A; Thu, 26 Jun 2025 18:17:18 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.64.64]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 4C6B718003FC; Thu, 26 Jun 2025 18:17:17 +0000 (UTC) From: Luiz Capitulino To: david@redhat.com, willy@infradead.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lcapitulino@gmail.com, shivankg@amd.com Subject: [PATCH 3/3] fs: stable_page_flags(): use snapshot_page() Date: Thu, 26 Jun 2025 14:16:53 -0400 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspam-User: X-Stat-Signature: 49x7wdaqhyhjito1r5r1fntdkrgpn76y X-Rspamd-Queue-Id: E03D840014 X-Rspamd-Server: rspam08 X-HE-Tag: 1750961841-660377 X-HE-Meta: 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 kuuaBorV Jm/GgWfjLIbj1TyNw/kqkzhWHWF6lFaHS+xUoNHlsl6CY+NHOjPDYTZ25fTXljMoy44L7RcrgOrbRjnzTpsieK8APLmbYH5/GGozsCLlrFI85OKwxms7ko+Hv4J9uuE/7DRC5MmoyoXEuIRT+LORS9xDIKvvaByienFd6Btm41IPRZzHa0UGXQ11nTqORA8ZPf35EA2Z1j4eZDpnelhRQQG06Hmgf6kEZvI/hxH2Bjg5ss0w9l47ILiGqud2I/4wYn0dh6G/cTel1WdGR4fyBnip4+A7v2T7Ac6eIY31E0ItRGnc06EfYeof2TLRwLGmGI51UDayvidkVfq2ncI/7KralM/4yJM4jArLwFfC2d+/sOcpeW69TN7Pq2lAzzZFtFPs1 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 | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff --git a/fs/proc/page.c b/fs/proc/page.c index 936f8bbe5a6f..a2ee95f727f0 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; @@ -189,10 +192,10 @@ 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 (ps.flags & PAGE_SNAPSHOT_PG_HUGE_ZERO) { 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; } @@ -200,14 +203,14 @@ u64 stable_page_flags(const struct page *page) * Caveats on high order pages: PG_buddy and PG_slab will only be set * on the head page. */ - if (PageBuddy(page)) + if (PageBuddy(&ps.page_snapshot)) u |= 1 << KPF_BUDDY; - else if (page_count(page) == 0 && is_free_buddy_page(page)) + else if (ps.flags & PAGE_SNAPSHOT_PG_FREE) 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 +218,7 @@ 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 +244,7 @@ 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); -- 2.49.0