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From: "Brendan Jackman" References: <20260710-spin-trylock-followup-v1-0-affb5fe5ed00@google.com> <20260710-spin-trylock-followup-v1-1-affb5fe5ed00@google.com> <20260710170311.e22bfd21c658e8357ceddeec@linux-foundation.org> <4c969202-a8ed-41a8-9e9a-281a12f6dde3@kernel.org> In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: yqtzga3w5dzqbtior759by4mgkc89ctd X-Rspamd-Queue-Id: 4858D180013 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1784023214-503083 X-HE-Meta: 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 iLVBrm2h tEpv6gN2g7WRnnbbggVTOYufwLOck6OkK/09VP3m8+ckRkLujT271RBRCcRRKbJ+9mUktCuZo3260nqwp1JjtUlNn4cMj9D7tEaRbEZHDfoBacRgmIzlFTDSIfinDFyGZk5/3voZY6VY2Hfp9ZZaL9E6CQZXheKBvmzx/edBLjA5hOzjRo8kuzwkqtJWgFYLFyaRNF7HQ8+2AwkNzd4jeohv26PDLmPS3tzh89fSKGhXtLrfMD2vpd0pxVnjOF/7IzaiZOjxS7HL4pqHHldrm1gBZ8G9/Cya/UafVARFohC2sRnxTL4+9gnVdE2/w+SKDP95MOAxac5r6wIZXpgE1wQHjvW21+7w6Q0ANmiphG105La00DNfzji0vww== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue Jul 14, 2026 at 9:52 AM UTC, Brendan Jackman wrote: > On Mon Jul 13, 2026 at 4:15 PM UTC, Harry Yoo wrote: >> >> >> On 7/13/26 11:31 PM, Brendan Jackman wrote: >>> On Sat Jul 11, 2026 at 12:03 AM UTC, Andrew Morton wrote: >>>> On Fri, 10 Jul 2026 10:42:20 +0000 Brendan Jackman wrote: >>>> >>>>> As noted in can_spin_trylock(), using this is unsafe in this context. >>>>> commit 620b46ed6ae17 ("mm/page_alloc: return NULL early from >>>>> alloc_frozen_pages_nolock() in NMI on UP") fixed this on the alloc si= de >>>>> but missed the free side. >> >> Ouch, do we allow alloc_pages() -> free_pages_nolock()? >> Didn't notice. > > We don't explicitly disallow that but I'd say it's "forbidden by > default"... Oh, the BPF arena code does it. >>>> Also, Sashiko might have found yet more pre-existing issues: >>>> https://sashiko.dev/#/patchset/20260710-spin-trylock-followup-v1-0-af= fb5fe5ed00@google.com >>>=20 >>> There are 2 cases here: >>>=20 >>> 1: !pcp_allowed_order() -> This is forbidden by alloc_order_allowed(), >>> quite a bad miss from Sashiko IMO. >> >> Hmm but alloc_order_allowed() would return true for !pcp_allowed_order() >> when spinning is allowed, then pages can be freed via >> free_pages_nolock()? So yeah Sashiko was right after all.