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b=aCNhk9191WRg6r+R2XCSmJGb9N XWpYCBqFGqjSuPZAdPk6o4CKReJBXt0pyJ0YNYvbfuErrkbzrlrNhADsUtIYQS9bvj2tS5Uihh81K QVvIciHWPeHBse8536TVD6l1Sf/9I3fxdZrKloib+zUmpbYGprwmbA8gDCqriOra8R8qX7Yb8kRzl Xzxi42+yhqMJHEx6pJO6/EK/dPBEWr/r63Nget93fY9H/dQmaEgKZJw8Oa4LPzOH2oRXQrPqom484 Iyi2AOHaVQgtFtbhbHJU1NrCrAgyHdJI1BUu/gFKM38WS1t4FIIi0X7QLB2TFOtlN0jM1aJXqbVp8 XeYfTlDA==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1wPiPN-0000000024Q-0NIZ; Wed, 20 May 2026 11:00:29 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, linux-mm@kvack.org, david@kernel.org, willy@infradead.org, surenb@google.com, hannes@cmpxchg.org, ljs@kernel.org, ziy@nvidia.com, usama.arif@linux.dev, fvdl@google.com, Rik van Riel Subject: [RFC PATCH 36/40] mm: page_alloc: set ALLOC_NOFRAGMENT on alloc_frozen_pages_nolock_noprof Date: Wed, 20 May 2026 10:59:42 -0400 Message-ID: <20260520150018.2491267-37-riel@surriel.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520150018.2491267-1-riel@surriel.com> References: <20260520150018.2491267-1-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: f74rd41s85yjtmcbj5geuzsdr7yzktmx X-Rspam-User: X-Rspamd-Queue-Id: 9D5A580013 X-Rspamd-Server: rspam07 X-HE-Tag: 1779289260-697238 X-HE-Meta: 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 57QiknC2 lG1NNKsioEPgZO4Scuw5AZm2VH2NC2VlnivRjUY0bSinMXeY6g8TOWcBgNpIjnVsyHFnu7wjpnAkQU1+HR+nzLyjHUBheJM0D9A6YgNlVVZrfGXfcHAW8pKMR3KF1Jm+sfsEJPRaYQEKXvMq3KP97T8FdB588SdUlOymfr5Ai0KfBPes9WPz/HiAQoXN6MijDS6GabJHCKTF+che3MMddwEYwC4vJYnZqoxWvo4mfz3RA0LxIaMz8IK5Q4jiHsK+WNqC/DcgayXlnIfzCbqAfJMxUNYu+jEcKoM3i7wQIRSLHSAZZsDqL/h3vnN/DjRe8Auck Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The no-lock atomic page allocator (alloc_frozen_pages_nolock) bypasses __alloc_pages_slowpath() entirely and calls get_page_from_freelist() directly. The slowpath is where ALLOC_NOFRAGMENT is normally set for non-movable allocations, so the nolock path runs without the "skip clean SPBs" guard. Add ALLOC_NOFRAGMENT to the alloc_flags. The function is best-effort and callers already handle NULL. The flag steers the alloc toward tainted-SPB sub-pageblock space first; for order > 0 the existing auto-refuse in the get_page_from_freelist relax sequence returns NULL when the tainted pool can serve a smaller order, and for order = 0 the alloc falls back to claiming a clean SPB only if the tainted pool is exhausted of suitable fragments. ALLOC_NOFRAGMENT is purely a pageblock-category steering hint; it does not depend on __GFP_DIRECT_RECLAIM and does not introduce any sleeping locks, so it composes cleanly with ALLOC_TRYLOCK in NMI, hardirq, and PREEMPT_RT contexts. Signed-off-by: Rik van Riel Assisted-by: Claude:claude-opus-4.7 syzkaller --- mm/page_alloc.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2791a52b61da..4e45fac14622 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -11525,7 +11525,23 @@ struct page *alloc_frozen_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned */ gfp_t alloc_gfp = __GFP_NOWARN | __GFP_ZERO | __GFP_NOMEMALLOC | __GFP_COMP | gfp_flags; - unsigned int alloc_flags = ALLOC_TRYLOCK; + /* + * ALLOC_NOFRAGMENT steers this best-effort no-lock allocation + * toward tainted-SPB sub-pageblock space before fragmenting any + * clean superpageblock. Without it, atomic kmalloc_nolock callers + * (e.g. BPF storage from sched_process_exec tracepoints) hit the + * fallback path on every PCP miss and convert a movable pageblock + * in a clean SPB to UNMOVABLE -- tainting a 1 GiB hugepage + * candidate for an order-0 atomic alloc. With NOFRAGMENT set: + * - order > 0: the get_page_from_freelist relax sequence + * auto-refuses to drop NOFRAGMENT when the tainted pool can + * serve a smaller order, returning NULL to the caller. + * - order = 0: prefers tainted-SPB fragments first; only falls + * back to claiming a clean-SPB pageblock if the tainted pool + * is exhausted of suitable fragments. + * Callers of alloc_pages_nolock() already handle NULL. + */ + unsigned int alloc_flags = ALLOC_TRYLOCK | ALLOC_NOFRAGMENT; struct alloc_context ac = { }; struct page *page; -- 2.54.0