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Tue, 02 Sep 2025 12:25:46 -0400 X-MC-Unique: bSUXBqyPNWqsMD_lkbXvuA-1 X-Mimecast-MFC-AGG-ID: bSUXBqyPNWqsMD_lkbXvuA_1756830345 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 983FE19560AD; Tue, 2 Sep 2025 16:25:45 +0000 (UTC) Received: from t14s.fritz.box (unknown [10.22.80.27]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id D482230001A7; Tue, 2 Sep 2025 16:25:43 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, David Hildenbrand Subject: [PATCH v2 1/2] selftests/mm: split_huge_page_test: fix occasional is_backed_by_folio() wrong results Date: Tue, 2 Sep 2025 18:25:35 +0200 Message-ID: <20250902162536.956465-2-david@redhat.com> In-Reply-To: <20250902162536.956465-1-david@redhat.com> References: <20250902162536.956465-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Rspamd-Queue-Id: 747AA1A0008 X-Rspam-User: X-Stat-Signature: 7b864yz91u6em1p18mokcopghf7pfy96 X-Rspamd-Server: rspam09 X-HE-Tag: 1756830350-784916 X-HE-Meta: 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 5ZgjSnSM NBLaNI2tE25D2dCEmNq9WRrbj90PKG5g/o3K/uajcLHCYqWqEnZ7Q0pQEC8Qt+3ChtFjbPxW1lMOnhUHMV/PTXxcxThLICUedjDGVCdPrrQIzbPFiI/1OmVSSSysK4163+MqHPu5O34y8S9z0tQ1QLE1qbvpHuFRwUqW1G99u+3E47QTg8DokTJEGikvhi+qkx2/+db+G4+0LSrBDRkc4OJC5nE3W8KDjlnEGNLtDsnHvUWf1PdxNq40WKevawW2Z6wpemXRysaxMpNM0jaAqFiacX0VsvvkK9NJ+wXDBGQhEus9nGZ5lzDW5c1Vf9+4BklSR9gDJKQfKj4axhSnkf+1rulVYYlj9mqA4WjhXrI7itn6WhnCh5V/0PwWcYu3g1IES 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: When checking for actual tail or head pages of a folio, we must make sure that the KPF_COMPOUND_HEAD/KPF_COMPOUND_TAIL flag is paired with KPF_THP. For example, if we have another large folio after our large folio in physical memory, our "pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL" would trigger even though it's actually a head page of the next folio. If is_backed_by_folio() returns a wrong result, split_pte_mapped_thp() can fail with "Some THPs are missing during mremap". Fix it by checking for head/tail pages of folios properly. Add folio_tail_flags/folio_head_flags to improve readability and use these masks also when just testing for any compound page. Fixes: 169b456b0162 ("selftests/mm: reimplement is_backed_by_thp() with more precise check") Signed-off-by: David Hildenbrand --- tools/testing/selftests/mm/split_huge_page_test.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c index 10ae65ea032f6..72d6d8bb329ed 100644 --- a/tools/testing/selftests/mm/split_huge_page_test.c +++ b/tools/testing/selftests/mm/split_huge_page_test.c @@ -44,6 +44,8 @@ int kpageflags_fd; static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, int kpageflags_fd) { + const uint64_t folio_head_flags = KPF_THP | KPF_COMPOUND_HEAD; + const uint64_t folio_tail_flags = KPF_THP | KPF_COMPOUND_TAIL; const unsigned long nr_pages = 1UL << order; unsigned long pfn_head; uint64_t pfn_flags; @@ -61,7 +63,7 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, /* check for order-0 pages */ if (!order) { - if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL)) + if (pfn_flags & (folio_head_flags | folio_tail_flags)) return false; return true; } @@ -76,14 +78,14 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, goto fail; /* head PFN has no compound_head flag set */ - if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD))) + if ((pfn_flags & folio_head_flags) != folio_head_flags) return false; /* check all tail PFN flags */ for (i = 1; i < nr_pages; i++) { if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags)) goto fail; - if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL))) + if ((pfn_flags & folio_tail_flags) != folio_tail_flags) return false; } @@ -94,11 +96,8 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd, if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags)) return true; - /* this folio is bigger than the given order */ - if (pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)) - return false; - - return true; + /* If we find another tail page, then the folio is larger. */ + return (pfn_flags & folio_tail_flags) != folio_tail_flags; fail: ksft_exit_fail_msg("Failed to get folio info\n"); return false; -- 2.50.1