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Mon, 07 Jul 2025 14:51:10 -0400 X-MC-Unique: 9b4PRsuxPeyOwnIMKPuVoQ-1 X-Mimecast-MFC-AGG-ID: 9b4PRsuxPeyOwnIMKPuVoQ_1751914269 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 396C018002ED; Mon, 7 Jul 2025 18:51:09 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.80.96]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 1679519560AB; Mon, 7 Jul 2025 18:51:07 +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 Subject: [PATCH v2 4/4] fs: stable_page_flags(): use snapshot_page() Date: Mon, 7 Jul 2025 14:50:46 -0400 Message-ID: <42122b9988871469f1311d71a608629f40c0c55d.1751914235.git.luizcap@redhat.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 48C1040003 X-Stat-Signature: tc13adxz7imi7kz3bzqxbkm1pg781w89 X-HE-Tag: 1751914275-839027 X-HE-Meta: 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 4e3cP7R7 rGmCe92DoTT2JA8yifKqHiFLrB9Z2PIzvYPnQukhCjT4H/qDkw9WFyOb1IOc740VudMRdTUtwyci4zBaCpaR0zqM1HaL3Nn0xg3pzYNXh+61k8reeQA2Bx1e5GAimOcxETrkwl81kU0wHcCZoZRpNLLMf+uOs3zVsDeA8aSreNp1VULEh1qJ9sAZQEd4U9Xm271c5cX7f6UrwhV1u9Iosz3xIRTfCABU1h3Gx13I90i+NFecVka7oDyVhSDADx5MTFSpY19V7zYHEB7clZanZly5jDpu/ArR4KBcQmF1vM1CpBgdvfh4GGhlN0f06ennzWxY+Bly+v+1p42smlUjJQ/gRpflkKEwHPh6q2x+OUtZhMwD2yCzKlXAOTKUPzuwkc1Ki 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..cb58f066eb31 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_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 +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